U.S. patent application number 11/274044 was filed with the patent office on 2006-07-13 for methods and apparatuses for thermal treatment of foods and other biomaterials, and products obtained thereby.
Invention is credited to Gary Cartwright, Pablo Coronel, David Parrott, Kandiyan Puthalath Sandeep, Josip Simunovic, Kenneth R. Swartzel, Van-Den Truong.
Application Number | 20060151533 11/274044 |
Document ID | / |
Family ID | 36337321 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060151533 |
Kind Code |
A1 |
Simunovic; Josip ; et
al. |
July 13, 2006 |
Methods and apparatuses for thermal treatment of foods and other
biomaterials, and products obtained thereby
Abstract
Methods and apparatuses for thermally treating flowable
materials using electromagnetic radiation, and foods and materials
obtained thereby. Also provided are methods of continuous flow
thermal treatment of biomaterials, apparatuses for performing the
same, and products prepared using the methods and/or
apparatuses.
Inventors: |
Simunovic; Josip; (Raleigh,
NC) ; Swartzel; Kenneth R.; (Raleigh, NC) ;
Truong; Van-Den; (Raleigh, NC) ; Cartwright;
Gary; (Apex, NC) ; Coronel; Pablo; (Cary,
NC) ; Sandeep; Kandiyan Puthalath; (Cary, NC)
; Parrott; David; (Raleigh, NC) |
Correspondence
Address: |
JENKINS, WILSON, TAYLOR & HUNT, P. A.
3100 TOWER BLVD
SUITE 1200
DURHAM
NC
27707
US
|
Family ID: |
36337321 |
Appl. No.: |
11/274044 |
Filed: |
November 14, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60627499 |
Nov 12, 2004 |
|
|
|
60664762 |
Mar 24, 2005 |
|
|
|
Current U.S.
Class: |
222/150 |
Current CPC
Class: |
A23L 3/22 20130101; A23L
3/01 20130101; A23L 3/005 20130101; A23L 3/225 20130101; A23V
2002/00 20130101; A23L 3/001 20130101; A61L 2/10 20130101; A23B
7/01 20130101 |
Class at
Publication: |
222/150 |
International
Class: |
B67D 1/08 20060101
B67D001/08 |
Claims
1. A process for thermally treating a flowable material while
passing the flowable material as a continuous stream through a
thermal treatment apparatus, the process comprising: (a) passing a
flowable material continuously through a conduit, wherein at least
a portion of the conduit is transparent to electromagnetic
radiation; (b) heating the flowable material by exposing the at
least a portion of the conduit that is transparent to
electromagnetic radiation; and (c) mixing the flowable material to
provide for thermal equalization in at least a portion of the
flowable material.
2. The process of claim 1, wherein the flowing occurs at a constant
flow rate.
3. The process of claim 1, wherein the flowing occurs at a constant
heating power input or at a constant mass mean temperature at the
heating exit for the flowing biomaterial.
4. The process of claim 1, wherein the flowable material is
selected based on at least one of rheological, dielectric, and
thermophysical properties, or combinations thereof, of the flowable
material.
5. The process of claim 1, wherein the flowable material is a
biomaterial.
6. The process of claim 5, wherein the biomaterial is a food
biomaterial.
7. The process of claim 6, wherein the food biomaterial is selected
based on at least one of rheological, dielectric, and
thermophysical properties, or combinations thereof, of the food
biomaterial.
8. The process of claim 1, wherein the heating results in an
average bulk temperature increase rate in the flowable material of
at least about 1 degree Fahrenheit per second or 0.5 degrees
Celsius per second.
9. The process of claim 8, comprising one or more additional
heating steps.
10. The process of claim 9, wherein the one or more additional
heating steps precedes, accompanies, or follows the heating that
results in an average bulk temperature increase rate in the
flowable material of at least 1 degree Fahrenheit per second or 0.5
degrees Celsius per second.
11. The process of claim 1, wherein the heating is substantially
free of heating by contacting the flowable material with a surface
having a temperature that exceeds a maximum temperature level of
the flowable material itself.
12. The process of claim 1, wherein the electromagnetic radiation
has a wavelength of about 1.times.10.sup.-4 meters or greater.
13. The process of claim 1, wherein the electromagnetic radiation
has a frequency of about 3.times.10.sup.12 waves per second or
less.
14. The process of claim 1, wherein the mixing occurs before,
during, or after the heating, and combinations thereof.
15. The process of claim 1, wherein the mixing is accomplished by
altering a cross-sectional geometry of the flow.
16. The process of claim 1, wherein the mixing occurs passively,
actively, or both actively and passively.
17. The process of claim 1, wherein the flowable biomaterial is not
subjected to a heated surface.
18. The process of claim 16, wherein the mixing is accomplished by
using at least one passive, active, or both passive and active
mixing devices, which serves to increase physical contact and heat
exchange between regions of the flowable material having a higher
temperature level and regions of the flowable material with a lower
temperature level, which would not occur in the absence of the
mixing devices.
19. The process of claim 18, wherein the mixing provides at least a
10% reduction in temperature distribution variability across the
flowable material when compared to temperature distribution
variability across the flowable material in the absence of the
mixing devices.
20. The process of claim 18, comprising placing the mixing devices
at a location selected from the group consisting of one or more
points of entry, one or more points within, one or more exits, and
combinations thereof, of the portion of the conduit that is exposed
to the electromagnetic radiation.
21. The process of claim 1, further comprising packaging the
flowable material for refrigerated storage.
22. The process of claim 1, wherein the heating and the mixing
provide a sufficient temperature for a sufficient time to
accomplish one of sterilization and pasteurization of the flowable
material.
23. The process of claim 22, further comprising aseptically
packaging the flowable material.
24. The process of claim 1, wherein the flowable biomaterial
contact surface is sterilized prior to introduction of the flowable
biomaterial.
25. The process of claim 23, comprising holding the flowable
material at a predetermined temperature for a predetermined length
of time, and cooling, packaging and hermetically sealing the
flowable material under aseptic conditions in a sterilized
package.
26. The process of claim 22, where the flowable material is filled
at a predetermined temperature level into a non-sterile package
under one of atmospheric and increased pressure conditions in order
to achieve concurrent sterilization of package surfaces in contact
with the flowable material and then hermetically sealing the
package.
27. A product produced by the process of claim 1.
28. A commercially sterile biomaterial having one or more quality
attributes that is preserved to a greater extent as compared to a
reference biomaterial that has been sterilized using a thermal
treatment method comprising contacting of the reference biomaterial
with a surface whose temperature is consistently higher than a
predetermined treatment temperature for the reference
biomaterial.
29. The commercially sterile food biomaterial of claim 28, wherein
the one or more quality attributes are preserved for at least 12
weeks of storage at about 25.degree. C.
30. The food biomaterial of claim 28, wherein the one or more
quality attributes is selected from the group consisting of
nutrient content, color, texture, flavor and general
appearance.
31. The food biomaterial of claim 28, wherein the food biomaterial
is one of hermetically packaged, shelf stable, and both
hermetically packaged and shelf stable.
32. The food biomaterial of one of claims 28 and 31, wherein the
food biomaterial is sweet potato.
33. A commercially sterile food biomaterial having one or more
quality attributes that is preserved to a greater extent as
compared to a reference food biomaterial that has been sterilized
using a thermal treatment method comprising contacting of the
reference food biomaterial with a surface whose temperature is
consistently higher than a predetermined treatment temperature for
the reference food biomaterial, wherein: (i) the food biomaterial
is one of packaged for refrigeration, hermetically packaged, shelf
stable, both packaged for refrigeration and shelf stable, and both
hermetically packaged and shelf stable; (ii) the food biomaterial
is sweet potato or white (e.g., Irish) potato, optionally a puree;
wherein optionally no preservatives or acidulants, such as but not
limited to an additive that makes the product more stable under
thermal treatment, have been added to the food biomaterial but
wherein optionally, water, salt, spices, flavors, peeling agents,
and/or sodium acid pyrophosphate and other anti-browning additives
can be added to or present in the food biomaterial.
34. A thermally treated food biomaterial having a quality profile
comprising one or quality attributes that substantially matches a
quality profile of an untreated food biomaterial of the same type,
wherein the thermally treated food biomaterial is commercially
sterile and shelf stable.
35. The food biomaterial of claim 34, wherein the quality attribute
is selected from the group consisting of nutrient content, color,
texture, flavor and general appearance.
36. The food biomaterial of claim 35, wherein the food biomaterial
is hermetically packaged.
37. The food biomaterial of claim 34, wherein the food biomaterial
is sweet potato.
38. A thermally treated food biomaterial having a quality profile
comprising one or quality attributes that substantially matches a
quality profile of an untreated food biomaterial of the same type,
wherein: (i) the thermally treated food biomaterial is one of
commercially sterile, packaged for refrigeration, hermetically
packaged, shelf stable, and any combination thereof; and (ii) the
food biomaterial is sweet potato or white (e.g., Irish) potato,
optionally a puree; wherein optionally no preservatives or
acidulants, such as but not limited to an additive that makes the
product more stable under thermal treatment, have been added to the
food biomaterial but wherein optionally, water, salt, spices,
flavors, peeling agents, and/or sodium acid pyrophosphate and other
anti-browning additives can be added to or present in the food
biomaterial.
39. An apparatus for thermally treating a flowable material, the
apparatus comprising: (a) a conduit for receiving a flowable
material, wherein at least a portion of the conduit is transparent
to electromagnetic radiation; (b) a device for providing
electromagnetic radiation to at least a portion of the conduit; and
(c) a mixing structure disposed within or along the conduit to
provide for thermal equalization in at least a portion of the
flowable material.
40. The apparatus of claim 39, wherein the electromagnetic
radiation can be provided at a wavelength of about
1.times.10.sup.-4 meters or greater.
41. The apparatus of claim 39, wherein the electromagnetic
radiation can be provided at a frequency of about 3.times.10.sup.12
waves per second or less.
42. The apparatus of claim 39, wherein the mixing structure
comprises an altered cross-sectional geometry of the conduit.
43. The apparatus of claim 39, wherein the mixing structure
comprises one or more passive mixing structures, one or more active
mixing structures, or both.
44. The apparatus of claim 43, comprising any combination of
passive, active, or both passive and active mixing structures which
serve to increase physical contact and heat exchange between
regions of a flowable material having a higher temperature level
and regions of the flowable material with a lower temperature
level, which would not occur in the absence of the mixing
structures.
45. The apparatus of claim 43, wherein the mixing structures
provide at least a 10% reduction in temperature distribution
variability (standard deviation) across the flowable material when
compared to temperature distribution variability (standard
deviation) across the flowable material in the absence of the
mixing structures.
46. The apparatus of claim 43, comprising mixing structures at a
location selected from the group consisting of one or more points
of entry, one or more points within, one or more exits, and
combinations thereof, of the portion of the conduit that is
transparent to electromagnetic radiation.
47. The apparatus of claim 39, comprising a control device for
controlling a flow through the conduit at a constant flow rate.
48. The apparatus of claim 39, comprising a control device for
controlling a flow through the conduit at a volumetric flow rate of
at least 0.25 gallons per minute.
49. The apparatus of claim 39, comprising a control device for
controlling a power level of the device for providing
electromagnetic radiation such that heating of a flowable material
in the conduit can occur at an average bulk temperature increase
rate in the flowable material of at least 1 degree Fahrenheit per
second or 0.5 degrees Celsius per second.
50. The apparatus of claim 39, comprising a control device for
controlling a power level of the device for providing
electromagnetic radiation such that heating of a flowable material
in the conduit occurs at a higher rate than heating of the conduit,
such the heating of the flowable material is substantially free of
heating by contacting the flowable material with a surface of the
conduit having a temperature that exceeds a maximum temperature
level of the flowable material itself.
51. The apparatus of claim 39, comprising a control device for
controlling a power level of the device for providing
electromagnetic radiation such that the power level can be
maintained constant.
52. The apparatus of claim 39, comprising a control device for
controlling a power level of the device for providing
electromagnetic radiation such that the power level can be preset
automatically or manually adjusted to a level predetermined to
provide a predetermined thermal treatment of the flowable
biomaterial at a predetermined mass flow rate.
53. The apparatus of claim 39, comprising a packaging device for
one of packaging the flowable material for refrigerated storage,
aseptically packaging the flowable material, and both packaging the
flowable material for refrigerated storage aseptically packaging
the flowable material.
54. The apparatus of claim 39, comprising a hold tube adapted for
fluid communication with the conduit.
55. The apparatus of claim 39, capable of having the flowable
biomaterial product contact surface rendered commercially sterile
prior to the introduction of the flowable biomaterial.
56. The product of claim 33 or claim 38, wherein the package can be
of any standard size, including but not limited to individual
size.
57. The product of claim 33 or claim 38, wherein the volume of food
biomaterial in the package exceeds a volume of food biomaterial
that can be accommodated in a Type 10 can.
58. A commercially sterile shelf stable food biomaterial, wherein
the food biomaterial comprises sweet potato or white potato and has
a shelf life of 24 weeks or more, and further wherein no
preservatives or acidulants that enhance stability of the food
biomaterial to thermal treatment have been added to the food
biomaterial, but wherein optionally the food biomaterial can
comprise one or more of water, salt, spices, flavors, peeling
agents, and sodium acid pyrophosphate and other anti-browning
additives.
59. The commercially sterile shelf stable food biomaterial of claim
58, wherein the food biomaterial is a puree.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based on and claims priority to U.S.
Provisional Application Ser. No. 60/627,499, filed Nov. 12, 2004,
and U.S. Provisional Application Ser. No. 60/664,762, filed Mar.
24, 2005, the disclosures of each of which are herein incorporated
by reference in their entireties.
TECHNICAL FIELD
[0002] The presently disclosed subject matter relates to methods
and apparatuses for thermally treating flowable materials using
electromagnetic radiation, and foods and materials obtained
thereby. More particularly, the presently disclosed subject matter
relates to methods of continuous flow thermal treatment of
biomaterials, apparatuses for performing the same, and products
prepared using the methods and/or apparatuses.
BACKGROUND
[0003] In order to be sold to the public, food often needs to be
treated to minimize microbial growth that can occur between the
time that the foodstuffs are harvested and they are purchased by
the consumer. There are several general methods that are
commercially available for this purpose, the most widespread of
which is to heat the material to appropriate temperatures for
sufficient lengths of time to kill or otherwise inactivate any
microorganisms and/or spores that could germinate and grow at the
storage temperature that may be present within the food. For
example, milk is typically pasteurized in order to reduce the
levels of bacteria that are normally found in the milk, which
allows milk to be stored safely longer than it would be otherwise
in the absence of the pasteurization process.
[0004] Generally, indirect heating methods are used in which the
biomaterials are passed through a chamber that is heated to
temperatures in excess of 60.degree. C. for some heat sensitive
pasteurizations to 100.degree. C. and up to 150.degree. C. to
render materials commercially sterile. The presence of the
biomaterials within the heated chambers results in the temperature
of the biomaterials increasing until they reach substantially the
same temperature as the surrounding chamber. However, many
foodstuffs and other biomaterials are negatively impacted by the
application of heat, either in terms of taste, aesthetic
appearance, nutrient levels, or other characteristics so that the
ways in which this material can be treated are limited.
Additionally, many biomaterials exposed to a heated surface will
burn on to the surface causing reduced heat flow, increased run
times and can produce off flavors within the product as run time
increases and heated material builds up and flakes off into the
product.
[0005] For example, the utilization of sweet potatoes in the food
industry often involves processing of the roots into purees that
can be subsequently frozen or canned to allow year-round
availability of the produce. The sweet potato puree (SPP) can be
used as an ingredient in various products, including baby food,
casseroles, puddings, pies, cakes, bread, restructured fries,
patties, soups and beverages (Truong, 1992; Truong et al., 1995;
Woolfe, 1992).
[0006] Preservation of SPP by freezing is a well-established
method, but the frozen puree requires considerable investment in
frozen distribution and storage as well as a lengthy and poorly
controlled defrosting treatment prior to use. Canned puree
typically requires excessive thermal treatment, especially when
processed in institutional-size packages, provides poor utilization
of storage space, and presents a difficulty in handling, opening,
and dispensing of the product, as well as disposing of the emptied
packages. Due to the poor heat penetration characteristic of the
puree, canned sweet potatoes are retorted for over 2 hours at
121.degree. C., resulting in product quality within a can that
varies drastically from the can center to the wall edges.
Particularly at the edges, the product is often severely
over-processed, resulting in dark discoloration and burnt flavor.
Thus, the useful can size is frequently limited to can size number
10 (i.e., a volume of about 13 cups), and this size limitation is a
major obstruction to the wider applications of canned sweetpotato
puree in the food processing industry.
[0007] Other thermal processing technologies such as scraped
surface heat exchangers or flash sterilization treatment also have
limitations in that SPP is characterized by low thermal diffusivity
(Smith et al., 1982). Fasina et al. (2003) reported that SPP has a
thermal diffusivity of the order of 3.times.10.sup.-7 m.sup.2/s and
a thermal conductivity of the order of 0.54 W/mK. The low thermal
diffusivity of SPP leads to very long periods of heating when
conventional thermal processing methods are used in order to
achieve required sterilization levels, which in turn causes
degradation of the nutrients in SPP and poor product quality.
[0008] Thus, there exists a long-felt and continuing need in the
art for effective methods to thermally treat foods and other
biomaterials. The presently disclosed subject matter addresses this
and other needs in the art.
SUMMARY
[0009] This Summary lists several embodiments of the presently
disclosed subject matter, and in many cases lists variations and
permutations of these embodiments. This Summary is merely exemplary
of the numerous and varied embodiments. Mention of one or more
representative features of a given embodiment is likewise
exemplary. Such an embodiment can typically exist with or without
the feature(s) mentioned; likewise, those features can be applied
to other embodiments of the presently disclosed subject matter,
whether listed in this Summary or not. To avoid excessive
repetition, this Summary does not list or suggest all possible
combinations of such features.
[0010] The presently disclosed subject matter provides processes
for thermally treating a flowable material while passing the
flowable material as a continuous stream through a thermal
treatment apparatus. In some embodiments, the process comprises (a)
passing a flowable material continuously through a conduit, wherein
at least a portion of the conduit is transparent to electromagnetic
radiation; (b) heating the flowable material by exposing the at
least a portion of the conduit that is transparent to
electromagnetic radiation; and (c) mixing the flowable material
within the conduit to provide for thermal equalization in at least
a portion of the flowable material. In some embodiments, the
flowing occurs at a constant flow rate. In some embodiments, the
flowing occurs at a constant heating power input or at a constant
mass mean temperature at the heating exit for the flowing
biomaterial.
[0011] In some embodiments, the flowable material is selected based
on at least one of rheological, dielectric, and thermophysical
properties, or combinations thereof, of the flowable material. In
some embodiments, the flowable material is a biomaterial. In some
embodiments, the biomaterial is a food biomaterial. In some
embodiments, the food biomaterial is selected based on at least one
of rheological, dielectric, and thermophysical properties, or
combinations thereof, of the food biomaterial.
[0012] In some embodiments of the presently disclosed subject
matter, the heating results in an average bulk temperature increase
rate in the flowable material of at least 1 degree Fahrenheit per
second or 0.5 degrees Celsius per second. In some embodiments, one
or more additional heating steps are employed. In some embodiments,
the one or more additional heating steps precedes, accompanies, or
follows the heating that results in an average bulk temperature
increase rate in the flowable material of at least 1 degree
Fahrenheit per second or 0.5 degrees Celsius per second. In some
embodiments, the heating is substantially free of heating by
contacting the flowable material with a surface having a
temperature that exceeds a maximum temperature level of the
flowable material itself.
[0013] In some embodiments of the presently disclosed subject
matter, the electromagnetic radiation has a wavelength of about
1.times.10.sup.-4 meters or greater. In some embodiments, the
electromagnetic radiation has a frequency of about
3.times.10.sup.12 waves per second or less.
[0014] In some embodiments of the presently disclosed subject
matter, the mixing precedes, accompanies, or follows the heating.
In some embodiments, the mixing is accomplished by altering a
cross-sectional geometry of the flow. In some embodiments, the
mixing occurs passively, actively, or both actively and passively.
In some embodiments, the mixing is accomplished by using any
combination of passive, active, or both passive and active mixing
devices which serve to increase physical contact and heat exchange
between regions of the flowable material having a higher
temperature level and regions of the flowable material with a lower
temperature level, which would not occur in the absence of the
mixing devices. In some embodiments, the mixing provides at least a
10% reduction in temperature distribution variability (standard
deviation) across the flowable material when compared to
temperature distribution variability (standard deviation) across
the flowable material in the absence of the mixing devices. In some
embodiments, the process comprises placing the mixing devices at a
location selected from the group consisting of one or more points
of entry, one or more points within, one or more exits, and
combinations thereof, of the portion of the conduit that is exposed
to the electromagnetic radiation.
[0015] In some embodiments of the presently disclosed subject
matter, the flowable biomaterial is not subjected to a heated
surface thereby providing a heater section without burned on
biomaterials and yielding beneficial process run times relative to
indirect heating systems.
[0016] In some embodiments, the heating and the mixing provide a
sufficient temperature for a sufficient time to accomplish one of
sterilization and pasteurization of the flowable material.
[0017] In some embodiments, the process further comprises packaging
the flowable material for refrigerated storage. In some
embodiments, the process further comprises aseptically packaging
the flowable material.
[0018] In some embodiments of the presently disclosed subject
matter, the flowable biomaterial contact surface is sterilized
prior to introduction of the flowable biomaterial. In some
embodiments, the process comprises holding the flowable material at
a predetermined temperature for a predetermined length of time, and
cooling, packaging and hermetically sealing the flowable material
under aseptic conditions in a sterilized package. In some
embodiments, the flowable material is filled at a predetermined
temperature level into a non-sterile package under one of
atmospheric and increased pressure conditions in order to achieve
concurrent sterilization of package surfaces in contact with the
flowable material and then hermetically sealing the package.
[0019] The presently disclosed subject matter also provides a
product produced by the processes disclosed herein.
[0020] The presently disclosed subject matter also provides a
commercially sterile food or other biomaterial having one or more
quality attributes that is preserved to a greater extent as
compared to a reference food or other biomaterial that has been
sterilized using a thermal treatment method comprising contacting
of the reference food or other biomaterial with a surface whose
temperature is consistently higher than a predetermined treatment
temperature for the reference food or other biomaterial. In some
embodiments, the one or more quality attributes are preserved for
at least 12 weeks of storage at about 25.degree. C. In some
embodiments, the one or more quality attributes is selected from
the group consisting of nutrient content, color, texture, flavor
and general appearance. In some embodiments, the food or other
biomaterial is one of hermetically packaged, shelf stable, and both
hermetically packaged and shelf stable. In some embodiments, the
food or other biomaterial is sweet potato or white (e.g., Irish)
potato.
[0021] The presently disclosed subject matter also provides a
commercially sterile food or other biomaterial having one or more
quality attributes that is preserved to a greater extent as
compared to a reference food or other biomaterial that has been
sterilized using a thermal treatment method comprising contacting
of the reference food or other biomaterial with a surface whose
temperature is consistently higher than a predetermined treatment
temperature for the reference food or other biomaterial, wherein:
(i) the food or other biomaterial is one of hermetically packaged,
shelf stable, and both hermetically packaged and shelf stable; (ii)
the food or other biomaterial is sweet potato or white (e.g.,
Irish) potato; and (iii) the volume of food or other biomaterial in
the package exceeds a volume of food or other biomaterial that can
be accommodated in a Type 10 can. In some embodiments, no
additional acid component has been added to the package.
[0022] The presently disclosed subject matter also provides a
thermally treated food or other biomaterial having a quality
profile comprising one or quality attributes that substantially
matches a quality profile of an untreated food or other biomaterial
of the same type, wherein the thermally treated food or other
biomaterial is commercially sterile and shelf stable. In some
embodiments, the quality attribute is selected from the group
consisting of nutrient content, color, texture, flavor and general
appearance. In some embodiments, the food or other biomaterial is
hermetically packaged. In some embodiments, the food or other
biomaterial is sweet potato or white (e.g., Irish) potato.
[0023] The presently disclosed subject matter also provides a
thermally treated food or other biomaterial having a quality
profile comprising one or quality attributes that substantially
matches a quality profile of an untreated food or other biomaterial
of the same type, wherein: (i) the thermally treated food or other
biomaterial is commercially sterile and shelf stable; (ii) the food
or other biomaterial is sweet potato or white (e.g., Irish) potato;
and (iii) the volume of food or other biomaterial in the package
exceeds a volume of food or other biomaterial that can be
accommodated in a Type 10 can. In some embodiments, no additional
acid component is added to the package.
[0024] The presently disclosed subject matter also provides
apparatuses for thermally treating a flowable material. In some
embodiments, the apparatus comprises (a) a conduit for receiving a
flowable material, wherein at least a portion of the conduit is
transparent to electromagnetic radiation; (b) a device for
providing electromagnetic radiation to at least a portion of the
conduit; and (c) a mixing structure disposed within or along the
conduit to provide for thermal equalization in at least a portion
of the flowable material. In some embodiments, the electromagnetic
radiation can be provided at a wavelength of about
1.times.10.sup.-4 meters or greater. In some embodiments, the
electromagnetic radiation can be provided at a frequency of about
3.times.10.sup.12 waves per second or less.
[0025] In some embodiments of the presently disclosed subject
matter, the mixing structure comprises an altered cross-sectional
geometry of the conduit. In some embodiments, the mixing structure
comprises one or more passive mixing structures, one or more active
mixing structures, or both. In some embodiments, the apparatus
comprises any combination of passive, active, or both passive and
active mixing structures which serve to increase physical contact
and heat exchange between regions of a flowable material having a
higher temperature level and regions of the flowable material with
a lower temperature level, which would not occur in the absence of
the mixing structures. In some embodiments, the mixing structures
provide at least a 10% reduction in temperature distribution
variability (standard deviation) across the flowable material when
compared to temperature distribution variability (standard
deviation) across the flowable material in the absence of the
mixing structures.
[0026] In some embodiments of the presently disclosed subject
matter, the apparatus comprises mixing structures at a location
selected from the group consisting of one or more points of entry,
one or more points within, one or more exits, and combinations
thereof, of the portion of the conduit that is transparent to
electromagnetic radiation. In some embodiments, the apparatus
comprises a control device for controlling a flow through the
conduit at a constant flow rate. In some embodiments, the apparatus
comprises a control device for controlling a flow through the
conduit at a volumetric flow rate of at least 0.25 gallons per
minute. In some embodiments, the apparatus comprises a control
device for controlling a power level of the device for providing
electromagnetic radiation such that heating of a flowable material
in the conduit can occur at an average bulk temperature increase
rate in the flowable material of at least 1 degree Fahrenheit per
second or 0.5 degrees Celsius per second. In some embodiments, the
apparatus comprises a control device for controlling a power level
of the device for providing electromagnetic radiation such that
heating of a flowable material in the conduit occurs at a higher
rate than heating of the conduit, such the heating of the flowable
material is substantially free of heating by contacting the
flowable material with a surface of the conduit having a
temperature that exceeds a maximum temperature level of the
flowable material itself. In some embodiments, the apparatus
comprises a control device for controlling a power level of the
device for providing electromagnetic radiation such that the power
level can be maintained constant. In some embodiments, the
apparatus comprises a control device for controlling a power level
of the device for providing electromagnetic radiation such that the
power level can be preset automatically or manually adjusted to a
level predetermined to provide a predetermined thermal treatment of
the flowable biomaterial at a predetermined mass flow rate. In some
embodiments, the apparatus comprises a packaging device for one of
packaging the flowable material for refrigerated storage,
aseptically packaging the flowable material, and both packaging the
flowable material for refrigerated storage aseptically packaging
the flowable material. In some embodiments, the apparatus comprises
a hold tube adapted for fluid communication with the conduit. And
in some embodiments, the apparatus is capable of having the
flowable biomaterial product contact surface rendered commercially
sterile prior to the introduction of the flowable biomaterial.
[0027] Accordingly, it is an object of the presently disclosed
subject matter to provide a method for thermally treating a
flowable material. This and other objects are achieved in whole or
in part by the presently disclosed subject matter.
[0028] An object of the presently disclosed subject matter having
been stated above, other objects and advantages of the presently
disclosed subject matter will become apparent to those of ordinary
skill in the art after a study of the following description of the
presently disclosed subject matter and non-limiting Examples.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a schematic diagram of one embodiment of the
thermal treatment system disclosed herein.
[0030] FIG. 2 is a plot depicting the dielectric properties of
sweetpotato puree (SPP) at 915 and 2450 MHz.
[0031] FIG. 3 is a graph showing how maximum operating diameter
(M.O.D.) relates to temperature for SPP at 915 MHz.
[0032] FIG. 4 depicts typical temperature profiles at the exit of
the heating section in the 5 kW tests.
[0033] FIG. 5 depicts the rheological properties of SPP samples
from the 5 kW tests.
[0034] FIG. 6 depicts color measurements of SPP samples from the 5
kW tests.
[0035] FIG. 7 depicts a typical temperature profile at the inlet of
the holding tube during the 60 kW test in the absence of static
mixers.
[0036] FIG. 8 depicts a typical temperature profile at the inlet of
the hold tube during the 60 kW test after static mixers were
introduced.
[0037] FIGS. 9 and 10 are schematic views depicting aspects of
representative embodiments of the presently disclosed apparatuses
used to thermally treat biomaterials.
[0038] FIGS. 11A-11I are schematic view of examples of microwave
and RF-transparent flow-through tubes/chambers and methods for
preparing the same.
[0039] FIG. 12 is a photograph of an installed two-stage continuous
flow microwave heater implementing two focused cylindrical
microwave heaters/reactors--locations of preceding, concurrent, or
subsequent mixing implementation are indicated (A, B, and C;
respectively).
[0040] FIGS. 13A-13C are a drawing and photographic images of a
tool for measurement and monitoring of cross-sectional temperature
distributions. The tool is a combination of single or several
multi-point thermocouple probes providing cross-sectional coverage
of the area perpendicular to the direction of material flow.
Positioning and utilizing such sensing and monitoring tools at key
locations (heater entry and exit and mixing element entry and exit)
has been used to test and document the uniformity and/or its
absence and illustrate the efficiency of a variety of mixing
implements and tools in achieving temperature equalization.
[0041] FIGS. 14A and 14B are schematic diagrams of an exemplary
mixing device, with a capability to provide the mechanical mixing
effect in all previously listed target locations (preceding,
concurrent and/or subsequent to heating) at the same time and using
the same device--this can be achieved by extending the mixing
element throughout these regions. The mixing element is fabricated
from a MW or RF-transparent material and provides a concurrently
rotating and orbiting movement within the exposure region, ensuring
that no configuration is static and minimizing the likelihood of
overheating and/or runaway heating within the transparent tube or
chamber.
[0042] FIG. 15 is a photograph showing the filling of the
sterilized product under aseptic fill conditions into a previously
sterilized bag. The product was subsequently proven to be shelf
stable and viable microbe-free after a 4-month storage under
ambient temperature storage conditions.
[0043] FIG. 16 is a graph of the temperature measurements acquired
during a recirculated, incremental heating run of an extremely
viscous, poorly thermally conductive vegetable homogenate:
sweetpotato puree.
[0044] FIG. 17 is a plot depicting the temperature distributions
that can be expected and encountered at flow rates and temperature
increase conditions approaching the industrial sterilization
levels. The graph displays temperatures at the exit of the 1.sup.st
stage of the 60 kW microwave heating installation. Temperature
distribution and variations are substantial. If such unfavorably
heated flow and temperature distribution were allowed to enter the
2.sup.nd heating stage in unmodified form, there would be a
possibility of developing extreme temperature and pressure
conditions and hazardous equipment and installation failures.
[0045] FIG. 18 is a plot depicting the temperature distribution and
values of the same flow stream after it has passed through the
1.sup.st static mixer installation. Temperature distribution is
significantly leveled, allowing for the introduction of the
material flow into the 2.sup.nd heating stage without significant
concern for possible failures.
[0046] FIG. 19 is a plot depicting the temperature distribution at
the cross section of the exit of the second heating stage. While
much narrower than the distribution recorded at the exit of the
1.sup.st heating stage; the distribution is still quite
significant. Some regions of the flow profile might not have
achieved the intended sterilization-level temperatures, in spite of
the on-target delivery of temperature increase for the bulk
material flow. If this temperature distribution was introduced into
the flow-through hold section without the necessary mixing step,
these flow regions (lower temperature) can be and stay in contact
with the external (colder) perimeter of the hold tube flow profile
and remain inappropriately sterilized, possibly resulting in
microbial product spoilage during storage.
[0047] FIG. 20 is a graph of the temperature distributions acquired
at the exit cross section of the 2.sup.nd static mixer, following
the 2.sup.nd heating stage. The distribution is clearly and
efficiently minimized and all monitored temperatures across the
flow cross-section reach or exceed the intended target
sterilization-level temperature. This allows for the safe
continuation of processing via entry into the hold tube section and
holding the material at a pre-set sterilization level temperature
for a pre-determined length of time. Sterility and subsequent
shelf-stability of the obtained product is thus achieved.
[0048] FIGS. 21-25 are plots depicting the equivalent processing
and temperature distribution profile sequence for another difficult
to process, high-viscosity, poor conductivity product--white
(Irish) potato puree (i.e., mashed potatoes). Attached figures are
equivalent to figures shown for the sweetpotato product--and cover
temperature distribution after recirculated heating using the 5 kW
installation (FIG. 21), unacceptably wide temperature distribution
at the exit of the 1.sup.st heating stage of a two-stage 60 kW
installation (FIG. 22), positive effect of utilizing a static mixer
following the 1.sup.st heating stage and the resultant significant
reduction in temperature variability and distribution (FIG. 23);
another relatively wide distribution of temperatures at the exit of
the 2.sup.nd heating stage (FIG. 24), and finally, a near-perfect,
very narrow distribution after the implementation of the 2.sup.nd
static mixing device (FIG. 25), allowing the entry of the material
into the holding section of the process, under controlled,
well-maintained and narrow temperature distribution conditions,
providing a superior process and a superior commercially sterile,
shelf-stable product.
[0049] FIGS. 26A and 26B depict the rheological properties of
carrot puree samples processed at various temperatures in the 5 kW
microwave unit.
[0050] FIG. 26A depicts the decrease in the dynamic viscosity
(.eta.*) of all carrot puree samples with increasing frequency,
showing pseudoplastic behavior. FIG. 26B depicts the frequency
dependency of the mechanical spectra of carrot puree with G' higher
than G'', indicating that the material can be classified as a weak
gel. Small strain oscillatory tests applied to the samples in these
figures allowed the evaluation of both the dynamic or complex
viscosity and gel strength of the tested materials without
disrupting the structural networks. These non-destructive
rheological tests were performed using the same stress-controlled
rheometer (Reologica Instruments AB, Lund, Sweden) as the high
shear rate ramps in FIG. 5, except that the sample was subjected to
gently oscillatory sweep at frequencies of 0.01 to 20 Hz.
[0051] FIGS. 27A and 27B depict the rheological properties of
carrot puree samples processed at various temperatures in the 60 kW
microwave unit.
[0052] FIG. 27A depicts the decrease in the dynamic viscosity
(.eta.*) of all carrot puree samples with increasing frequency.
FIG. 27B depicts the frequency dependency of the mechanical spectra
of carrot puree with G' higher than G'', indicating that the
material can be classified as a weak gel. FIGS. 27A and 27B also
show disrupting of the bonding and gel networks as indicated by
significant decreases in both .eta.* and G'. Severe disruptions of
the consistency and gel strength of the carrot puree were observed
with heating time beyond 30 minutes.
[0053] FIGS. 28A and 28B depict the rheological properties of green
pea puree samples processed at various temperatures in the 5 kW
microwave unit.
[0054] FIG. 28A depicts the decrease in dynamic viscosity (.eta.*)
of all green pea puree samples with increasing frequency, showing
pseudoplastic behavior. FIG. 28B shows that the green pea puree can
be considered a weak gel since its mechanical spectra exhibited
frequency dependency with G' higher than G''.
[0055] FIGS. 29A and 29B depict the rheological properties of green
pea puree samples processed at various temperatures in the 60 kW
microwave unit.
[0056] FIGS. 29A and 29B show that in contrast to carrot puree,
.eta.* and G' of the green pea puree initially decreased upon
heating to 75-110.degree. C., as compared to the unheated sample,
and then significantly increased at higher temperatures
(120-130.degree. C.). This trend was also exhibited among the
samples heated up to 125.degree. C. and re-circulated for 6
hours.
[0057] FIG. 30 depicts the color determination for green pea puree
samples collected from the 60 kW tests. As depicted in FIG. 30, the
L* value (lightness) and the b* value (yellowness) were slightly
affected by microwaving temperature and time (<5% decreases).
However, the loss in green color (a* values) was about 30% with
reference to the unheated sample for the green pea puree heated to
125.degree. C. With increasing heating time at 125.degree. C. as in
conventional thermal processing, the green color (a* values) of the
puree was further degraded by 38% as compared to the unheated
samples.
[0058] FIGS. 31A and 31B depict the results of rheological testing
of sweetpotato puree microwaved to 130.degree. C. and stored in
aseptic packages at ambient conditions. Storage at ambient
conditions had no effect on the rheological properties of the
puree. The stored samples retained the dynamic viscosity and
(.eta.*) and gel strength (G') comparable to those of the frozen
stored puree.
[0059] FIG. 32 depicts the color values of the microwaved
sweetpotato puree as compared to frozen and canned purees (canned
sweetpotato puree; can size no. 10) purchased directly from a local
sweetpotato cannery. Microwave processing resulted in an increase
of 25% in b* value (yellowness), slight decreases in a* (redness;
<1%) and L* values (lightness; <2%), as compared to the
frozen puree. Storage of the aseptic puree for 3 months at
22.degree. C. further decreased the a* and L* values by 2.2% and
4.5%, respectively, while the b* value was about 15% higher than
that of the frozen puree. The canned puree had dark brown color
with L* values about 10.5% and 7.5% lower than those of the frozen
puree.
[0060] FIGS. 33-36 present color degradation data and projections
for worst-case scenario under all conditions compared.
[0061] FIG. 37 is a schematic plot comparing Fo values and Co
values of a MW-based process as disclosed herein versus
conventional aseptic processing and canning approaches.
[0062] FIG. 38 is a schematic diagram of the high-temperature color
degradation assembly employed in Example 10.
[0063] FIG. 39 is a photograph of the experimental setup described
in Example 10.
[0064] FIG. 40 is a photograph showing a sample chamber assembly,
and special tri-clamp with a Smart gasket port containing the
3-point thermocouple probe in contact with the sample material
described in Example 10.
DETAILED DESCRIPTION
I. General Considerations
[0065] Continuous flow microwave heating is one of the emerging
technologies in food processing, offering fast and efficient
heating. Uniform heating of dairy products using this technology
has been shown in previous tests (Coronel et al. 2003). The heating
of food products using microwaves is governed by the dielectric
properties of the material. The dielectric properties of
sweetpotato puree (SPP), as reported in Fasina et al., 2003, are
within a similar range as other products that have been identified
as promising for processing using continuous flow microwave heating
systems (Coronel et al., 2004). In some embodiments, the presently
disclosed subject matter represents the first disclosure related to
an aseptically packaged and shelf-stable vegetable puree processed
by a continuous flow microwave heating system and methods for
preparing the same.
[0066] The presently disclosed subject matter provides processes as
well as a family of new products. The processes described are
unique combinations of material (pumpable food or other
biomaterial) transport, exposure to electromagnetic energy, and
temperature control via active or passive temperature equalization.
The mentioned temperature equalization provides a secondary means
of thermal equalization by preceding, accompanying, or following a
rapid temperature-increase stage achieved by the exposure of the
flowing food or other biomaterial to the electromagnetic energy
field (radio frequency or microwave frequency range) during pumping
through a chamber or a tube made of a microwave (MW) and/or radio
frequency (RF) transparent material.
[0067] The exposure to the electromagnetic energy field during
material transport (pumping) through the MW and/or RF
energy-transparent flow-through chamber or tube can be effected in
a single or multiple stages, provided that at least one of the
heating stages results in an average bulk temperature increase rate
of at least 1 degree Fahrenheit per second or 0.5 degrees Celsius
per second.
[0068] In some embodiments, the material being treated is
transported (pumped) through the transparent chamber/tube through
which this minimum temperature increase rate is effected at a
volumetric flow rate of at least 0.25 gallons per minute, however
different flow rates can be employed.
[0069] The mechanical temperature equalization step can be effected
by using any combination of static or active mixing devices, which
serve to increase physical contact and heat exchange between the
continuously flowing material regions having a higher temperature
level and material regions or streams with a lower temperature
level that would not normally occur without the introduction of
these mixing elements. Mechanical temperature equalization steps
can be implemented via any individual or combinations of treatments
or devices preceding, concurrent, or subsequent to the above
described exposure to the electromagnetic energy field. The
mechanical mixing stage typically delivers at least a 10% reduction
in the temperature distribution variability (standard deviation)
across the material flow when compared to the variability (standard
deviation) of temperature distribution without the implemented
(active or passive, preceding, concurrent, and subsequent) mixing
elements; at the points of entry, points within, and/or at the exit
of the electromagnetic-energy exposure stage (MW and/or
RF-transparent chamber/tube).
[0070] The disclosed processes are also unique regarding the
absence of heated surfaces implemented to achieving the temperature
increases needed for sterilization. That means that under normal
processing conditions temperatures of any and all surfaces that
processed materials are directly contacting never exceed the
maximum temperature level within the product mass itself.
[0071] All listed treatments and devices are implemented prior to
the confirmation (by measurement) of the appropriate temperature
and/or time-temperature history levels required for the achievement
of commercial sterility. Following the described procedures, the
food or other biomaterial can either be (a) held at a predetermined
temperature level or range for a predetermined length of time
(typically using a hold-tube section of an aseptic processing
system), cooled and packaged and hermetically sealed under aseptic
conditions into a previously and separately sterilized package; (b)
filled hot (at a predetermined temperature level) into a
non-sterile package under either atmospheric or increased pressure
conditions in order to achieve concurrent sterilization of package
surfaces in contact with the food or other biomaterial being
sterilized as well as the material itself. In this instance the
package is hermetically sealed while the contained product is still
hot.
[0072] In either case, the resulting hermetically packaged, shelf
stable, commercially sterile product comprises a food or other
biomaterial with unique chemical and physical properties: quality
attributes such as nutrient content, color, texture, flavor and
general appearance are preserved to a much higher extent than when
these products are sterilized using any other commercially
available method (in-pack sterilization, hot-filling using
conventional/indirect continuous flow heating methods including
tube in tube heat exchangers, scraped surface heat exchangers, as
well as other types of heat exchangers implementing hot-surface
conventional heat exchange principles). The one or quality
attributes can be preserved to in some embodiments at least a 5%
greater extent, in some embodiments at least a 10% greater extent,
in some embodiments at least a 15% greater extent, in some
embodiments at least 20% greater extent, in some embodiments at
least a 25% greater extent, and in some embodiments at least 30%
greater extent or more as compared to a reference food or other
biomaterial that has been sterilized using a thermal treatment
method comprising contacting of the reference food or other
biomaterial with a surface whose temperature is consistently higher
than a predetermined treatment temperature for the reference food
or other biomaterial.
[0073] The presently disclosed subject matter provides new
processes utilizing a combination of available and newly developed
processing elements to achieve the rapid food and other biomaterial
sterilization while minimizing quality loss and maximizing nutrient
retention compared with the products sterilized using conventional
thermal processing (either batch or continuous). The obtained
package sizes and ranges of the obtained products can range from a
single-serving size to packages containing very large quantities
(for example, 100 gallons or more). The product quality is
uniformly high throughout the package size range, making the
process and generated products compatible with a wide range of
potential processed materials and markets, including further
processing, institutional distribution (restaurants, cafeterias,
hospitals, etc.) as well as export markets for either direct
consumption or further processing into other value-added
products.
[0074] The present disclosure defines the conditions of thermal
process and treatment delivery for the production of thermally
treated, shelf stable, commercially sterile food and other
biomaterial products. The products and materials processed by the
described methods can be either high acid or low acid. The
presently disclosed subject matter provides the most significant
advantages when applied to viscous foods and other biomaterials
with high contents of carbohydrates and/or proteins.
[0075] The presently disclosed subject matter also introduces
active and/or static mixing elements as a means of temperature
equalization prior to, during, and/or subsequent to heating by a
single-stage or multiple exposure to electromagnetic (microwave
and/or radio frequency or any combination of frequencies covering
the range defined as radio frequency and/or microwave) energy
during continuous flow transport through a transparent flow-through
chamber or tube.
[0076] The present technology to achieve the temperature levels and
temperature level distribution necessary to achieve rapid
sterilization for the production of shelf-stable, commercially
sterile products relies primarily on heat exchange via indirect
heating and contact of the food or other biomaterial with heated
surfaces. This results in low rates of heat exchange and low rates
of bulk material temperature increase and necessitates extended
times of exposure to hot surfaces and associated extended
degradation of quality attributes such as nutrient content, flavor,
color, general appearance and texture. Often biomaterials are
burned on to the heat exchange surface rendering reduced heat
transfer and process run times. Flaking of burned on materials can
also yield end product off flavors. In a very limited number of
cases, more rapid heat delivery can be achieved by direct contact
of the material processed with superheated steam via steam
injection into the product or infusion of product into a
superheated steam environment. In both cases, composition of
material is negatively affected and there is a need for subsequent
removal of added water from the product. Additionally, these
methods are applicable only to a small and narrow group of products
with very high coefficients of thermal diffusivity allowing the
rapid heat dissipation necessary to achieve the needed rapid
heat-up. For thicker, more viscous or homogeneous materials with
suspended solid particles these methods are not applicable.
[0077] In some embodiments, one of the elements of the presently
disclosed subject matter is a group of viscous or weak gel
materials with a high carbohydrate content and/or high protein
content and products demonstrating shear thinning with a yield
stress obtained by implementing the disclosed sterilization
procedure; specifically shelf-stable high carbohydrate and/or
protein content products.
[0078] The unique characteristics of these products can vary from
material to material but there are several common elements: [0079]
the products are in a pumpable state in order to achieve the
continuous transportation mode throughout the processing and
packaging stages [0080] the retained quality attributes and
characteristics of the sterilized, shelf stable products obtained
by implementing the presently disclosed subject matter are closer
to the original material attributes and characteristics than is the
case with products and materials obtained by any other currently
available processing and preservation procedure. These attributes
and characteristics can be the rate of protein
degradation/denaturation (minimized); rate of color, viscosity,
texture, flavor, and/or nutrient content retention (maximized)
and/or the rate of undesirable chemical and physical changes
outside of criteria outlined above (minimized). Depending on the
processed material, these criteria can refer to the retention of
various chemical constituents such as thermo-sensitive vitamins
(vitamin C/ascorbic acid; .beta.-carotene/vitamin A; thiamine;
etc.) or naturally occurring pigments and/or antioxidants
(chlorophylls, carotenoids, anthocyanins, etc.) [0081] the high
level of retained attributes and characteristics is uniform
throughout the packaged environment (i.e., the variability and the
range of these characteristics is minimal in all points within the
package), regardless of the package size and shape (which is not
the case with the currently available similar shelf stable
products)
[0082] Recently, much has been learned about the new sophisticated
devices for delivery of rapid heating treatments to the
continuously flowing streams of foods and other biomaterials.
Treatments like rapid heating using ohmic, electroheating, radio
frequency, and microwave energy all claim the speed and efficiency
required to deliver the desired level and rate of heat to the
processed materials.
[0083] Possibly the most sophisticated and advanced family of
devices of this type are the patented cylindrical microwave
heaters/reactors, produced by Industrial Microwave Systems of
Morrisville, N.C., United States of America. These devices are
constructed using precise modeling and fabrication of proprietary
focusing structures that are carefully matched to a selected target
material in order to achieve a uniform heating rate and uniform
temperature distribution in the material exiting the heater/reactor
exposure cavity.
[0084] Unfortunately, this precise coupling of the design to a
selected set of material properties, while presenting a very clear
and impressive technical advantage in the theoretical sense, also
presents the most significant shortcoming of this technology in the
practical application sense; and may have, over time, become the
largest hurdle in its wider industrial and commercial
implementation.
[0085] The reasons for this are multiple. While the achievement of
a theoretically perfect (uniform) temperature distribution for a
single material under a single tightly defined set of conditions
would be desirable, such well defined material property sets and
tightly defined sets of conditions are rarely encountered in the
real world of food and other biomaterial processing.
[0086] The alternative of investing in a number of separate and
individual reactor/heater devices, each requiring a disassembly and
re-assembly of a process line in order to accommodate a narrowly
defined material from a possibly very wide range that a processor
could target, would be very costly and cumbersome.
[0087] Property and process parameter conditions that should be
considered in the implementation of continuous flow microwave
and/or radio frequency treatment are numerous, and can be
inter-dependent on other conditions such as temperature,
implemented shear rates, and accompanying physical and chemical
changes occurring in the material during the process, including but
not limited to the following: [0088] Dielectric properties
(properties determining the rate and efficiency of conversion of
microwave energy into heat) of the material are dependent on
temperature, composition, and accompanying physical and chemical
changes. Foods and other biomaterials are well-known for their
variability of composition so even when the treatment is perfectly
matched to a certain set of material properties, natural variations
due to growing conditions, cultivation practices, types of
cultivar, season, presence or absence of pests as well as local and
seasonal climate can affect the composition of the materials and
therefore the resulting match and efficiency and quality of
microwave and/or RF treatment. [0089] Design of the focused
applicator devices is typically centered on a single or a narrow
range of dielectric properties (assumed on the basis of a single or
a narrow temperature range of exposure during processing). However,
temperature differences achieved during heating far exceed the
ranges assumed in the design of processing elements. This leads in
some cases in reduction in energy coupling efficiency as well as
reduced temperature uniformity and expanded (in some cases
drastically) temperature distribution variabilities for product
types and temperature ranges not taken into account during the
design. [0090] Flow distribution of product during and subsequent
to heating is dependent on temperature range, volumetric and mass
flow rates, and physical properties of transported material such as
viscosity and texture. In most cases these properties are both
temperature and shear rate dependent. In addition to the typical
cases of laminar and turbulent flow profiles there is an infinite
number of intermediate and unique flow distribution scenarios
including channeling of material caused by local heating and
reduction of viscosity due to increased temperature and shear
rates. This all adds up to an extremely complex set of encountered
and potential conditions which cannot be reasonably addressed and
incorporated into a well-controlled sterilization process using a
selected narrow set of conditions for heating model approach.
[0091] Sterilized foods and other biomaterials undergo an
overwhelming number and variety of chemical and physical changes
during exposure to the sterilization level thermal treatments.
These include the uptake and release of water from various
biopolymer and macromolecule structures present in the foods and
other biomaterials (water associated with protein, carbohydrate and
polysaccharide molecules). This water can be bound and released
based on a variety of conditions, including, but not limited to pH,
temperature, concentration of solutes or solids, ionic strength of
the environment, etc. Additional changes affecting the dielectric,
flow and heat dissipation behavior of the processed material
include unfolding and denaturation of proteins, formation and
breakdown of gels (such as pectin and starch based gels), changes
in physical state such as melting and/or solidification of lipid
constituents. Finally, chemical changes and reactions affect not
only the physical and especially dielectric properties but also
result in generation (exothermic) or consumption (endothermic) of
thermal energy, additionally resulting in associated temperature
increases and/or reductions in the material, unrelated to the
heating process and method itself.
[0092] Taken together, all of the listed and additional factors and
parameters can limit the application of narrowly defined and
targeted focusing devices to a few cases where either these changes
are non-existent or minimal or where the thermal diffusivity
properties or the natural flow turbulence are so high as to provide
a concurrent temperature equalization effect with the flow.
Unfortunately, these materials are typically of low value, falling
short of justifying the cost of investment in a sophisticated, high
cost sterilization equipment such as RF or MW heating units, and
can be easily and more economically processed by other available
means.
[0093] Furthermore, currently available modeling and simulation
techniques and computing equipment can only provide an
approximation of the listed changes and variations. Very valuable
information and understanding can be gained from these models as
their sophistication increases and more elements are integrated
into simulations. However, they still currently fall short of
providing a sufficient, comprehensive basis to address all elements
and parameters needed to interpret these complex processes
appropriately.
[0094] The presently disclosed subject matter thus presents a
practical solution to these concerns. By incorporating the
additional mixing and temperature equalization devices into the
process under a wider set of operating conditions and much wider
target range of potential materials while maintaining the use of a
single type or construction design of energy focusing device, at
least two advantages can be achieved. For example, by
implementation of static or active mechanical mixing as an approach
for temperature equalization preceding, accompanying, or following
the heating via exposure to an electromagnetic energy field, the
presently disclosed subject matter provides a practical strategy
for expanding the range of targeted processed products, temperature
range, flow rate, and distribution conditions, and can additionally
accommodate and equalize effects from all parameters and events in
the above list; and (b) when combined with active or static mixing,
the methods and implementation of the expensive focusing structures
is not as critical for the rapid achievement of sterilization-level
temperatures at acceptable uniformity and distribution conditions.
Stated another way, the apparatuses and methods described herein
can expand the range of applicability of alternative focused and
non-focused methods of electromagnetic energy exposure and delivery
of rapid sterilization rates and effects.
[0095] A large number and variety of foods and other biomaterials
are compatible with the disclosed processes and apparatuses. Pureed
and homogenized fruits can be treated to the appropriate
temperature levels (95-100.degree. C.) for sterilization
preservation of high-acid materials and either filled hot or cooled
and filled under aseptic conditions.
[0096] Preliminary data has been generated by the co-inventors for
more than 50 different foods and materials using the recirculated
heating technique to evaluate and illustrate the temperature
distributions encountered and the need to address these
distributions by static or active mixing during the process.
[0097] The disclosures of the following patents and patent
publications are incorporated herein by reference in their
entireties: U.S. Pat. Nos. 6,797,929; 6,583,395; 6,406,727;
6,265,702; 6,121,594; 6,087,642; and 5,998,774; U.S. Patent
Application Publications 20030205576 and 20010035407; and PCT
International Patent Application Publications WO 0143508; WO
0184889; and WO 0036879.
II. Definitions
[0098] While the following terms are believed to be well understood
by one of ordinary skill in the art, the following definitions are
set forth to facilitate explanation of the presently claimed
subject matter.
[0099] Following long-standing patent law convention, the terms
"a", "an", and "the" refer to "one or more" when used herein,
including in the claims.
[0100] As used herein, the term "about", when referring to a value
or an amount, for example, relative to another measure, is meant to
encompass variations of in some embodiments .+-.20%, in some
embodiments .+-.10%, in some embodiments .+-.5%, in some
embodiments .+-.1%, and in some embodiments .+-.0.1% from the
specified value or amount, as such variations are appropriate.
[0101] As used herein, "significance" or "significant" relates to a
statistical analysis of the probability that there is a non-random
association between two or more entities. To determine whether or
not a relationship is "significant" or has "significance",
statistical manipulations of the data can be performed to calculate
a probability, expressed in some embodiments as a "p-value". Those
p-values that fall below a user-defined cutoff point are regarded
as significant. In some embodiments, a p-value less than or equal
to 0.05, in some embodiments less than 0.01, in some embodiments
less than 0.005, and in some embodiments less than 0.001, are
regarded as significant.
[0102] The presently disclosed subject matter provides a continuous
flow method for thermally treating a flowable material. As used
herein, the term "flowable material" refers to any material that
can be flowed from one point to another in a substantially uniform
manner. For example, in some embodiments, a flowable material can
be moved from one place to another under laminar flow. In some
embodiments, a flowable material comprises a highly
viscous/semi-solid material that is shear thinning or shear
thickening characterized with a yield stress.
[0103] In some embodiments the biomaterial is selected based on the
rheological, dielectric, and thermophysical properties of the
biomaterial. In some embodiments, the biomaterial has one or more
characteristics selected from the group consisting of high starch
content, high protein content, high solids content, a high
viscosity (for example, a viscosity at about 25.degree. C. that
renders conventional thermal treatment processes undesirable), and
low thermal conductivity (for example, (less than 1 W/mK). In some
embodiments, the biomaterial includes thick vegetable purees, weak
gels of biomaterials, and the like. Representative flow properties
and yield stress of thick/viscous foods or biomaterials including
sweet potato puree are presented in Tables 1 and 2. TABLE-US-00001
TABLE 1 Flow Properties of Various Food Biomaterials at 25.degree.
C. Consistency Flow behavior coefficient index Yield stress Food
Product Solid (%) (K) (n) (Pa) Sweetpotato 16 18.8 0.39 89 puree
A.sup.1 Sweetpotato 20 13.39 0.25 10 puree B.sup.2 Baby food, 15 28
0.59 28 banana (Gerber) Baby food, 16 1.4 0.6 13 peach Pear puree
18 2.3 0.49 3.5 Pear puree 45.7 35.5 0.48 33.9 Apple sauce 11 11.6
0.34 11.6 Apple sauce 18 34 0.42 34 Tomato paste 30 208 0.27 206
.sup.1Co-inventors' data reported in Coronel et al., 2004.
.sup.2Reported in Kyerreme et al., 1999.
[0104] TABLE-US-00002 TABLE 2 Yield Stress of Fluid Foods
Measurement Product .sigma..sub.o (Pa) Method Source Ketchup 22.8
extrapolation Ofoli et al., 1987 Mustard 34.0 extrapolation Ofoli
et al., 1987 Miracle Whip 54.3 extrapolation Ofoli et al., 1987
Apricot puree 17.4 extrapolation Ofoli et al., 1987 Milk chocolate
10.9 extrapolation Ofoli et al., 1987 Minced fish paste 1600-2300
extrapolation Nakayama et al., 1980 Mayonnaise 24.8-26.9 stress to
initiate De Kee et al., flow 1980 Ketchup 15.4-16.0 stress to
initiate De Kee et al., flow 1980 Tomato paste 83.9-84.9 stress to
initiate De Kee et al., flow 1980 Raw meat batter 17.9
extrapolation Toledo et al., 1977 Tomato puree 23.0 stress decay
Charm, 1962 Applesauce 58.6 stress decay Charm, 1962 Tomato paste
107-135 squeezing flow Campanella & Pelegi, 1987 Ketchup 18-30
squeezing flow Campanella & Pelegi, 1987 Mustard 52-78
squeezing flow Campanella & Pelegi, 1987 Mayonnaise 81-91
squeezing flow Campanella & Pelegi, 1987 Applesauce 45-87
squeezing flow Campanella & Pelegi, 1987 Applesauce 46-82 vane
method Qui & Rao, 1988 Ketchup 26-30 vane method Missaire et
al., 1990 Spaghetti sauce 24-28 vane method Missaire et al., 1990
Tomato puree 25-34 vane method Missaire et al., 1990 Pumpkin
filling 20 vane method Missaire et al., 1990 Applesauce 38-46 vane
method Missaire et al., 1990 Baby food, pears 49 vane method
Missaire et al., 1990 Baby food, 25 vane method Missaire et al.,
peaches 1990 Baby food, 71 vane method Missaire et al., carrots
1990 See also Steffe, 1996.
[0105] As used herein, the term "thermally treating" and
grammatical variants thereof refer to exposing a flowable material
(for example, a biomaterial) to conditions whereby the temperature
of all of the flowable material, either over time or upon exposure
to electromagnetic radiation with mixing, is increased to an
appropriate level to effect the treatment. In some embodiments, a
thermal treatment is designed to pasteurize or sterilize a
biomaterial.
[0106] As used herein, the terms "pasteurization" and "pasteurized"
refer to treatments sufficient to kill sufficient pathogenic
microorganisms contained within the biomaterial being treated to
render the biomaterial edible or otherwise administrable to a
subject without threat of infection by, for example, Salmonella,
Listeria, or other pathogenic microorganisms. Pasteurization can be
thought of as a treatment that, for all practical purposes, renders
pathogenic microorganisms into a state in which they are incapable
of reproducing or growing under refrigerated conditions.
Pasteurization methods cause in some embodiments at least a four
log cycle reduction, in some embodiments at least a six log cycle
reduction, and in some embodiments at least a nine log cycle
reduction, of bacteria in the product.
[0107] As used herein, the term "ultrapasteurization" refers to
pasteurization that results in a pasteurized product with a salable
shelf life under ambient or refrigerated conditions (e.g.,
4.degree. C. or less, but above freezing) greater than that
obtainable using previously known pasteurization methods. See e.g.,
U.S. Pat. No. 4,808,425 (the disclosures of all patents cited
herein are incorporated herein in their entireties). As used
herein, the phrase "salable shelf life" refers to an amount of time
that a product can be stored and/or available for sale to a
consumer before some characteristic that changes during storage
alters the product to an extent that would make the product
unappealing to the consumer. Representative characteristics that
can change during storage of a product include, but are not limited
to color levels, viscosity levels, taste characteristics, aromas,
and microbial levels. Thus, ultrapasteurization methods produce
extended salable shelf life products: for example, products having
shelf lives of in some embodiments more than 10 days, in some
embodiments more than 14 days, in some embodiments 4 to 6 weeks,
and in some embodiments up to 36 weeks or more.
[0108] In some embodiments, ultrapasteurization refers to a)
sterilizing the contact surface area of the processing unit prior
to introduction of the biomaterial, b) providing a thermal
treatment to the biomaterial greater than that normally associated
with pasteurization but less than would be considered commercially
sterile, although treatments in the range of the commercially
sterile range can be used, c) packaging in an Extended Shelf Life
(ESL) filler and/or aseptic filler and d) maintaining the product
under refrigeration during storage. Ultrapasteurized product is not
considered a low-acid shelf stable product requiring a no rejection
letter from the US Food and Drug Administration allowing production
but must be refrigerated and has a limited shelf life.
[0109] In some embodiments, the thermal treatment results in a
biomaterial that is shelf stable. As used herein, the term "shelf
stable" refers to a biomaterial that can be stored for extended
periods of time at room temperature without spoilage or microbial
growth when compared to the same biomaterial that had not been
thermally treated as described herein. A shelf stable biomaterial
can be stored at room temperature for in some embodiments more than
10 days, in some embodiments more than 14 days, in some embodiments
4 to 6 weeks, and in some embodiments up to 36 weeks or more
without spoilage or microbial growth. It is not uncommon for shelf
stable commercially sterile product to have shelf lives of one year
or greater.
[0110] Shelf stable and commercially sterile can be used
interchangeably for the purpose of the presently disclosed subject
matter. Elements include a) sterilizing the contact surface area of
the processing unit prior to introduction of the biomaterial, b)
providing a thermal treatment to the biomaterial that eliminates
the risks, within statistical limits, for the growth of
microorganisms and their spores, at ambient temperatures c)
packaging in hermetically sealed containers using an aseptic filler
and d) maintaining the product at ambient temperature during
distribution storage. Low-acid shelf stable product requires a no
rejection letter from the US Food and Drug Administration allowing
production.
[0111] It should be noted that "shelf stable" and "salable shelf
life" are not necessarily interchangeable terms. For example, a
product can be shelf stable for a period of time that exceeds its
salable shelf life. Given that certain changes that can occur to a
product over time are unrelated to microbial growth and can
negatively affect a salable shelf life, a given product's salable
shelf life is typically shorter than the time period during which
is it otherwise shelf stable.
[0112] The term "aseptic packaging" or packaged in an aseptic
filler means to the exclusion of microorganisms and their spores
other than those carried by the product itself. Aseptic packaging
fillers are pre-sterilized prior to production runs. In some
embodiments, the aseptic packaging material is pre-sterilized prior
to the introduction of heat-treated biomaterial.
[0113] By the term "biomaterial", it is meant that any material
that includes a biological component, such as a protein, starch, or
sugar. Representative biomaterials are those amenable to processing
using a thermal process, such as a continuous flow thermal process.
In some embodiments, a biomaterial is a food or a food product.
[0114] The term "biomaterial" is also meant to refer to solid or
fluid materials or products that are susceptible to deviations from
a standard quality or characteristic if exposed to certain
environmental conditions, or if not properly treated so as to reach
the standard characteristic or quality. In some embodiments,
"biomaterial" refers to a food material. The term "biomaterial" is
thus also meant to include a material or product that is to be
ingested by or introduced into a consumer.
[0115] Foods and other biomaterials, for example, are susceptible
to deviations from a standard quality or characteristic. Microbial
growth in the food or other biomaterial contained in a package can
occur if, among other things, the food or other biomaterial in the
package is not properly refrigerated or is not thermally treated to
a sufficient level to kill microbes and their spores within the
food or other biomaterial. Microbial growth produces deviations in
a characteristic in the food or other biomaterial from a standard
characteristic. For example, microbial growth can produce gases
within a package containing a food or other biomaterial. The gases,
mainly carbon dioxide produced by microbial metabolic processes,
represent a deviation from a standard characteristic of the food or
other biomaterial in a like package in that no such gases should be
present in a standard quality food or other biomaterial in a like
package. Further, the microbial growth itself can represent a
deviation for the standard, that is, no microbial growth.
[0116] Other examples of a "biomaterial" include pharmaceuticals,
blood and blood products, and personal health products like
shampoo. While personal health care products like shampoo are not
meant to be ingested by a consumer, they usually include a
biological component like a protein.
[0117] By the term "characteristic", it is meant a feature of the
biomaterial or of the package for a biomaterial. Particularly, the
term "characteristic" is meant to describe a feature of the
biomaterial or of the package of biomaterial that determines
whether or not the biomaterial or package is suitable for use by
and/or ingestion by a consumer. The term "quality attribute" can
include any characteristic disclosed herein that might be desirable
for a given biomaterial. The term "quality profile" can thus refer
to any combination of characteristics, or quality attributes,
disclosed herein that might be desirable for a given
biomaterial.
[0118] By the term "standard characteristic", it is meant, then, a
characteristic of the biomaterial and/or package for a biomaterial
which indicates that the biomaterial and/or package for a
biomaterial is suitable for use by a consumer. In some embodiments,
the term "standard characteristic" can mean a standard or a quality
level for a given characteristic against which unknown
characteristics can be compared.
[0119] For example, the characteristic and the standard
characteristic of the biomaterial can each comprise a
characteristic of the composition of the biomaterial. As used
herein, a "characteristic" can be a "quality attribute", which is
intended to refer to a characteristic of the biomaterial that when
varied affects the desirability of the treated biomaterial for the
consumer. Representative quality attributes include, but are not
limited to, nutrient content, color, texture, flavor, general
appearance, fat content, water composition, and combinations
thereof.
[0120] As used herein, the term "thermal equalization" refers to a
condition whereby the temperature of a biomaterial is substantially
uniform through a chosen region (for example, a cross section).
Thus, "thermal equalization" is a state wherein the temperature
distribution variability across the chosen region is minimized.
While it is not required that the temperature of the chosen region
be within any set number of degrees, thermal equalization can
encompass temperature variability of in some embodiments not more
than 20.degree. C., in some embodiments not more than 15.degree.
C., in some embodiments not more than 10.degree. C., in some
embodiments not more than 8.degree. C., in some embodiments not
more than 6.degree. C., in some embodiments not more than 5.degree.
C., in some embodiments not more than 3.degree. C., and in some
embodiments not more than 1.degree. C. Alternatively, thermal
equalization can be expressed in terms of a percent variability
through a chosen region (for example, a cross section). Thus, a
percent variability can encompass in some embodiments less than a
20%, in some embodiments less than a 15%, in some embodiments less
than a 10%, in some embodiments less than an 8%, in some
embodiments less than a 5%, in some embodiments less than a 3%, in
some embodiments less than a 2%, and in some embodiments less than
a 1% difference between the highest and the lowest temperatures
present within the chosen region.
[0121] In some embodiments, thermal equalization encompasses
temperature differences that are small enough such that the minimum
temperature is sufficient to accomplish the goals of the thermal
treatment without negatively affecting characteristics of interest
of the biomaterial at any site within the chosen region.
[0122] In some embodiments, mixing the flowable material
facilitates thermal equalization. In some embodiments, mixing is
accomplished by static or dynamic change of shape, profile and/or
area size of the cross-section of the flow-through region of a
conduit, preceding, concurrent or subsequent to heating/exposure to
electromagnetic energy. Shape can refer to the cross-sectional
geometry of the conduit, which can be varied from round to
elliptical to triangular etc.; change in profile can refer to the
inclusion of inserts such as single or multiple mixing bars,
shafts, or other such protrusions; and size of the area can refer
to an increase or decrease in the flow-through diameter of the
conduit as well as variations in the flow-through area by having
different cross sections and/or attachments to the mixing bars or
static flow obstructions.
[0123] As is well known in the art, by the term "hermetically
sealed", it is meant any sealing process wherein a package
including a material (e.g., a biomaterial) is sealed to the
exclusion of microbes and their spores. In the case of a
biomaterial, the biomaterial is treated prior to sealing, whether
thermally or otherwise, to remove microbes and their spores. An
appropriately treated biomaterial that is appropriately
hermetically sealed in a package will likely remain fit for
ingestion or other use by a consumer for an extended period of
time, assuming other appropriate storage conditions are implemented
as necessary. Thus, the term "hermetically sealed package" or
alternatively, the term "hermetically packaged" can be further
defined as a package having a seal that keeps a biomaterial
contained within the package fit for ingestion or other use by a
consumer for an extended period of time.
[0124] By the term "sterilizing", "sterilization", and grammatical
variants thereof, it is meant that the product is free of viable
organisms or spores capable of growing under any conditions (can
not be isolated and grown under optimum laboratory conditions.) In
some embodiments a commercial sterile product is desired. By the
term "commercially sterile" it is meant the condition achieved by
application of heat, sufficient, alone or in combination with other
ingredients and/or treatments to render the product free of
microorganisms and/or spores capable of growing in the product at
conditions at which the product is intended to be held during
distribution and storage non-refrigerated, ambient temperatures.
Commercially sterile products may have spores that could germinate
and grow under some conditions but not storage conditions intended
for the product. In no case would any spores that grow in the
commercially sterile product be pathogenic.
[0125] By the term "thermal property", it is meant any property of
a flowable material (e.g., a biomaterial) that is related to the
way the material (e.g., biomaterial) accepts or releases heat.
Examples include, but are not limited to, thermal conductivity, or
rate of heat penetration, rate of cooling, temperature, and
combinations thereof. Representative thermal properties include
rate of temperature changes, including rate of heat penetration and
rate of cooling.
[0126] The methods of the presently disclosed subject matter can be
employed in continuous flow treatment. As used herein, "continuous
flow treatment" refers to methods in which a continuous stream of
product is maintained in the treatment apparatus being used.
Continuous flow thermal processing equipment can comprise heating,
holding, and cooling sections, in which a continuous stream of
product is maintained.
[0127] The equivalent point method can be used for evaluating
thermal treatments be applied in practicing the presently disclosed
subject matter when continuous flow treatment is used. This method
describes the total thermal treatment received by a product in
continuous flow equipment. Procedures for using the equivalent
point method for analyzing the thermal effects on products during
continuous flow heating have been previously outlined (Swartzel,
1982; Swartzel, 1986; U.S. Pat. No. 4,808,425) and are known to
those skilled in the art.
[0128] In some embodiments, the presently disclosed subject matter
utilizes that portion of the electromagnetic spectrum associated
with microwaves and with radio reception (i.e., radio waves having
a frequency of from about 500 Kilohertz (KHz) to about 110
Megahertz (MHz); or radio waves with wavelengths from about 1 meter
to 10.sup.4 meters). In particular, the presently disclosed subject
matter uses high frequency electromagnetic radiation. As used
herein, the phrase "high frequency electromagnetic radiation"
(HFER) refers to electromagnetic radiation understood by those in
the art to include radio frequencies and microwaves. Thus, HFER can
have a frequency of about 3.times.10.sup.12 waves per second or
less, in some embodiments, from about 15 MHz to about 300 GHz. HFER
can have wavelengths of about 1.times.10.sup.-4 meters or greater,
and in some embodiments from about 1 millimeter to about 20 meters.
Alternating currents generate electromagnetic waves of a desired
frequency and wavelength, which travel at a speed characteristic of
the media in which they are traveling. The wavelength (.lamda.) of
a particular wave in a given flowable material (e.g., a
biomaterial) is determined from knowledge of the frequency f, which
remains constant (a function of the generator), and v, which
depends on the velocity of the wave in the product.
[0129] In some embodiments, the presently disclosed subject matter
involves microwave heating. The frequencies employed for microwave
heating encompass the entire range classified as microwaves. Only
four specific frequency bands are used for industrial heating
applications in the United States. These four bands were allocated
by the Federal Communications Commission and are called the
Industrial-Scientific-Medical or ISM frequencies. These bands are
at frequencies of 915 MHz, 2450 MHz, 5800 MHz, and 24,125 MHz.
Users of industrial microwave equipment are permitted to generate
unlimited power on these four bands, chosen so that they do not
interfere with radar and communications. While the presently
disclosed subject matter can incorporate the application of ISM
frequency heating, the presently disclosed subject matter is not
limited to these selected frequencies.
[0130] The presently disclosed subject matter utilizes HFER to
produce heat within the products being treated, causing microbial
destruction without loss of product functionality, and yielding
reduced or eliminated product deposition on surfaces in direct
contact with the biomaterial. Microbial inactivation using
electromagnetic waves can be due to thermal effects, as in
conventional heating processes, can include thermal effects
resulting from unknown interactions between biochemical
constituents of microbes and an electromagnetic field, and
combinations thereof. See e.g., Adey, 1989. However,
electromagnetic waves producing heat generally yield microbial
destruction at a level similar to that produced using conventional
heat only. See e.g., Goldblith, 1975.
[0131] In the presently disclosed subject matter, HFER is converted
to heat as it interacts with flowable materials (e.g.,
biomaterials). Absorption of electromagnetic energy increases the
kinetic energy of the molecules of the absorbing medium, and
increases the temperature of the absorbing medium. Because heat is
generated within the product being heated, contact with heated
surfaces acting as heat transfer surfaces is not required. Thus,
fouling or burning of biomaterials in contact with heated surfaces
is reduced or eliminated when using HFER treatment. In continuous
flow equipment, this allows extended process run-times and yields
greater efficiency by achieving higher through-put of product
before cleaning of equipment is required, while producing product
with good functional characteristics and eliminating burned flaked
off material that had adhered to the heat exchanger wall yielding
potentially off flavors.
[0132] Most continuous flow treatment processes using indirect heat
exchangers are designed to maximize turbulent, high-shear flow in
order to achieve efficient heat transfer throughout the flowable
material (e.g., biomaterial). In HFER heating, particulate matter
heats at the same rate as liquids, allowing continuous flow
treatment apparatuses to be designed with less concern about the
flow characteristics of the biomaterial. Shear stress on the
proteins can be reduced, and the need to make highly homogeneous
liquids from biomaterials can be eliminated. Thus, low shear pumps
can be employed in practicing the presently disclosed subject
matter in continuous flow apparatuses.
[0133] HFER heating is distinguished from ohmic heating in that the
heater design and controls are not dependent on the specific
electrical conductivity of the material being heated. For example,
different biomaterials can have sufficiently different electrical
conductance such that it is extremely difficult to heat them with
the same ohmic heater, while a HFER process and apparatus in
accordance with the presently disclosed subject matter should be
able to heat each product equally efficiently. HFER heating does
not create free radicals and the resulting deterioration of flavor
as is found when high energy ionizing radiation is used to treat
various biomaterials.
[0134] Any method for generating electromagnetic waves of the
desired frequencies can be used to carry out the presently
disclosed subject matter. Any commercial or industrial generator
capable of producing high frequency radio waves or microwaves can
be used. Generators can be added in parallel or in series to
increase production or temperature: Generators can be harmonically
suppressed or otherwise structured to meet standards for desired
electromagnetic emissions.
[0135] In apparatus used for practicing the methods of the
presently disclosed subject matter, structures which are interposed
between the product to be treated and the HFRW generator are
constructed of material that is transparent to electromagnetic
radiation. As used herein, the phrase "transparent to
electromagnetic radiation" refers to a characteristic of a material
whereby electromagnetic radiation (for example, radio frequencies
or microwaves) substantially passes through the material.
Similarly, the terms "radiolucent" and "microwave transparent"
refer to material that is permeable to radio waves and microwaves,
respectively. For example, in a continuous flow apparatus as
exemplified in FIG. 1, the conduit carrying the biomaterial
adjacent to the HFRW generator is manufactured of material that is
radiolucent or microwave transparent. As used herein, the term
"radiolucent" refers to a material that is essentially transparent
to radio waves of the frequency used in the methods of the
presently disclosed subject matter; while the material can be
permeable to electromagnetic waves of other frequencies, this is
not required. Similarly, the term "microwave transparent" refers to
a material that is essentially transparent to microwaves. Examples
of suitable radiolucent and/or microwave transparent materials
include polytetrafluoroethylene (e.g., the products marketed as
TEFLON.TM. or HOSTAFLON.TM.), and polycarbonate resins such as
LEXAN.TM., or glass (e.g., KIMAX.TM. tempered glass process pipe).
As would be apparent to one skilled in the art, the use of
radiolucent and/or microwave transparent materials is required only
to the extent necessary to allow sufficient exposure of the
biomaterial to the HFER.
[0136] In continuous flow apparatus used with methods of the
presently disclosed subject matter, any device for establishing a
continuous stream of flowable material (e.g., biomaterial) can be
used to carry out the presently disclosed subject matter. An
exemplary pump that can be used to establish the stream is a
positive displacement pump, though a positive displacement pump
(timing pumps) are generally needed to precisely define the holding
time of a product stream in a holding section. Positive
displacement pumps can be used in combination with other pumping
devices, such as centrifugal pumps.
[0137] Upon a review of the present disclosure, it will be apparent
to one skilled in the art that an adequate flow of flowable
material through the apparatus must be produced so that the
flowable materials are conveyed through the treatment apparatus at
an adequate rate. Representative devices for producing a flow of
flowable material (e.g., a biomaterial) include, but are not
limited to, gravity flow conduits and pumps such as SINE PUMPS.TM.
(Sine Pumps, Curacao, Netherlands Antilles), auger type pumps, or
combinations thereof. Reversible thermal set carrier medium gels
can also be used (e.g., methylcellulose solutions).
[0138] Using the methods and apparatuses of the presently disclosed
subject matter, it is possible to treat biomaterials from
temperatures below 40.degree. F. (but above freezing) up to
temperatures above 160.degree. F., but below cooking temperatures.
The product can then be held at the final temperature for a period
of time adequate to destroy harmful and spoilage bacteria, as
discussed below.
[0139] An optional preheating step can be employed prior to HFER
treatment to preheat the flowable material (e.g., biomaterial) to a
temperature between about 120.degree. F. and 155.degree. F.
Preheating systems can comprise, but are not limited to,
conventional heating systems such as plate, swept, tube heat
exchangers, ohmic systems, steam injection, hot water injection,
hot fluid food injection, etc.
[0140] In some embodiments, the total thermal treatment received by
a flowable material (e.g., a biomaterial) during the process must
be sufficient to reduce the microbiological population in the
product to an acceptable level. Proper thermal treatment can be
facilitated by presetting the holding times. The term "holding
time", as used herein, has its ordinary meaning as used in the
industry.
[0141] In some embodiments, the thermal treatment is sufficient to
produce a product having a shelf life of about four weeks to about
thirty-six weeks under ambient or refrigerated conditions, and in
some embodiments a product having a shelf life of about eight weeks
to about thirty-six weeks under ambient or refrigerated conditions.
The term "refrigerated," as used herein, means stored at or below a
temperature of 4.degree. C. but above freezing.
[0142] To produce uniformly treated flowable material (e.g.,
biomaterial), each unit of the flowable material (e.g.,
biomaterial) should receive substantially the same thermal
treatment. This can be accomplished in accordance with the
presently disclosed subject matter by exposing each unit of
flowable material (e.g., biomaterial) to the same HFER energy and
mixing, with other conditions being substantially uniform.
[0143] Following thermal treatment the product can then be cooled
using conventional cooling systems such as, but not limited to,
plate heat exchangers, swept surface heat exchangers, liquid
nitrogen injection, CO.sub.2 gas injection or injection of other
inert gases, or immersion in a water bath.
[0144] Elements of continuous flow apparatus are interconnected by
a product line formed of any conventional sanitary material, such
as stainless steel tubing.
[0145] To obtain a product with reduced quantities of
microorganisms, the treatment apparatus can be sterilized before
the biomaterial is passed therethrough. Sterilizing can be
accomplished by passing hot water under pressure through the
treatment apparatus, as is known in the art, so that hot water is
contacted to those surfaces which contact the product at a
temperature and pressure and for a time sufficient to sterilize
these surfaces. Any other method of sterilization of treatment
apparatuses can also be used.
[0146] Unpackaged flowable material (e.g., biomaterial) can be
aseptically packaged after treatment. "Aseptically packaged" means
packaged to the exclusion of microorganisms other than those
carried by the material itself, if any. Equipment suitable for
aseptically packaging biomaterial, such as the TETRA PAK.TM. TBA/9,
the TETRA PAK.TM. TR7-ESL, the TETRA PAK.TM. Model AB-3-250 (all
available from Tetra-Pak Inc., Vernon Hills, Ill., United States of
America), and the Evergreen EQ-4 (Evergreen Packaging Equipment,
Cedar Rapids, Iowa, United States of America), is commercially
available. Also useful in carrying out this step is equipment which
packages the product to the substantial exclusion of
microorganisms, known in the industry as "clean fillers," but the
greater exclusion of microorganisms provided by aseptic fillers
makes aseptic fillers preferable, particularly in view of the
ability of Listeria and certain other microorganisms to grow under
refrigerated conditions.
[0147] A homogenization step for unpackaged flowable biomaterial
can optionally be included, but generally is not required. The term
"homogenization" as used herein, means to subject a product to
physical forces to reduce particle size. Such procedures are known
in the art, and can be carried out on different types of equipment.
In some embodiments, this homogenizing step is carried out with
homogenizing equipment at total pressures of from about 500 pounds
per square inch (p.s.i.) to about 3,000 p.s.i.
[0148] Referring now to FIG. 37, another description of a quality
profile is provided, which pertains in part to concept of what can
be shown for time zero. Particularly, FIG. 37 shows that the MW
technique is very uniform, both in cold spot and average (bulk)
heating. The Co values correlate to quality factors-design with Ea
values (z values in the quality constituent range). Thus, this
industry standard can be used to represent the quality changes (for
the example, the quality profile) in the product at time zero. The
cold spot is also shown for an aseptic conventional flow product
(for example, purees typically flow as laminar flow-thus 2.times.
can optionally be used--fastest to bulk). It is thus believed that
there is a large difference between meeting the minimum legal Fo
for the cold spot and the bulk that is exposed for a MW-based
process as disclosed herein versus conventional aseptic processing
and canning approaches. For example, to get the cold spot in a
canning approach (2 hours of heating-#10 can) to the minimum Fo
value the bulk would be 80 min. Also, for canning vegetable purees,
the retorting time required for can size no. 10 is 165 minutes at
121C (Lopez 1987), the Fo values should be longer time periods.
[0149] With respect to shelf life, it is believed that the
presently disclosed product are within the industry standards for
usable product (for example, based on viscosity, color, aroma and
trained sensory evaluation and remains shelf stable through 18
months as compared to usable canned and aseptic, traditional, on
the market). However, referring to FIG. 37, it is believed that by
starting at time zero with much higher bulk (average) quality
retention (based on the Co value-which can also be shown as a ratio
of 100% time zero raw to, for example, 95% time zero processed
quality retention) and assuming the same kinetic degradation of
quality in all three methods stored at ambient temperature, one
might see 30-50% loss at time zero for the bulk in conventional
canned product and conventional aseptically processed product.
Thus, if it assumed that the difference stays the same over
storage, the quality at the 18 months level should be still
satisfactory for a product as disclosed herein, while poor for the
canned and for a conventional aseptic method.
[0150] FIG. 37 is thus believed to demonstrate the MW advantages
over the canned and conventional aseptic methods. Additional
advantages of a MW approach as disclosed herein include space
requirements, e.g., <1 foot MW heating tube vs. 250 ft for
conventional technology.
III. Apparatuses
[0151] III.A. Treatment Apparatuses
[0152] Referring now to the Figures, where like reference numerals
refer to like parts throughout, an apparatus for thermally treating
a flowable material is generally referred to as 10. Referring now
to FIGS. 1, 9 and 10, apparatus 10 comprises hopper 12, into which
a biomaterial preparation PR is loaded. Hopper 12 is in flow (or
fluid) communication with pump 14, and pump 14 is controlled to
provide a flow of biomaterial preparation PR through apparatus 10.
The direction of flow in FIGS. 1, 9 and 10 is indicated by arrows
18, 30, and 44.
[0153] Continuing with FIGS. 1, 9 and 10, apparatus 10 can comprise
a conduit 15 for receiving a flowable material, such as preparation
PR. Conduit 15 comprises a series of conduit sections 16, 20, 22,
24, 26, 28, 32, 34, 36, and 38. Conduit sections 22 and 26 are
transparent to electromagnetic radiation e.g., MW and/or RF
radiation). Apparatus 10 also includes one or more of temperature
sensors T1, T2, T3, T4, T5, T6, T7, T8, and T9, which are used to
monitor temperatures throughout apparatus 10, as described herein
below.
[0154] Continuing with FIGS. 1, 9 and 10, apparatus 10 comprises
device 40 and 42 for providing electromagnetic radiation to at
least a portion of conduit 15. Devices 38 and 40 comprise
generators G1 and G2, respectively, and heaters H1 and H2,
respectively, and provide any desired form of electromagnetic
radiation, such as but not limited to microwave (MW) radiation and
radio frequency (RF) radiation. Device 42 is show in dashed lines
in that it is optionally included in apparatus 10 as shown in FIGS.
9 and 10. Devices 40 and 42 are positioned to provide
electromagnetic radiation to conduit sections 22 and 26, as show by
arrows MW/RF (arrow shown in dashed lines for device 42).
[0155] Continuing with FIG. 9, a mixing structure M1 is disposed
within or along conduit sections 20, 22, 24, 26, and 28 to provide
for thermal equalization in at least a portion of the flowable
preparation PR. Referring particularly to FIG. 10, apparatus 10
comprises mixing structures M1', M2, M3, M4, and M5 at a locations
including but not limited to one or more points of entry (e.g., P1,
P4), one or more points within (P2, P5), one or more exits (P3,
P6), and combinations thereof, of sections 22 and 26 of conduit 15
that is transparent to electromagnetic radiation.
[0156] In some embodiments, mixing structures M1, M1', M2, M3, M4,
and M5 can comprise an altered cross-sectional geometry of conduit
sections. In some embodiments mixing structures M1, M1', M2, M3,
M4, and M5 can comprise one or more passive mixing structures, one
or more active mixing structures, or both. Indeed, in some
embodiments, mixing structures M1, M1', M2, M3, M4, and M5 can
comprise any combination of passive, active, or both passive and
active mixing structures which serve to increase physical contact
and heat exchange between regions of preparation PR having a higher
temperature level and regions of preparation PR with a lower
temperature level, which would not occur in the absence of the
mixing structures. In some embodiments, mixing structures M1, M1',
M2, M3, M4, and M5 can provide at least a 10% reduction in
temperature distribution variability (standard deviation) across
flowable preparation PR when compared to temperature distribution
variability (standard deviation) across flowable preparation PR in
the absence of the mixing structures.
[0157] Referring again to FIGS. 1, 9 and 10, apparatus 10 can
comprise a control device CD. Control device CD can control flow
through conduit 15. The flow rate can be a constant flow rate, for
example, a volumetric flow rate of at least 0.25 gallons per
minute. Control device CD can control a power level of devices 40
and/or 42 for providing electromagnetic radiation. For example, the
power level can be controlled such that heating of a flowable
material in the conduit can occur at an average bulk temperature
increase rate in the flowable material of at least 1 degree
Fahrenheit per second or 0.5 degrees Celsius per second. Control
device CD can control a power level of devices 40 and/or 42 for
providing electromagnetic radiation such that heating of
preparation PR in conduit 15 occurs at a higher rate than heating
of conduit 15, such the heating of preparation PR is substantially
free of heating by contacting preparation PR with a surface of
conduit 15 having a temperature that exceeds a maximum temperature
level of flowable preparation PR itself. Control device CD can
control a power level of devices 40 and/or 42 such that the power
level can be maintained constant. Control device CD can control a
power level of devices 40 and/or 42 such that the power level can
be preset automatically or manually adjusted to a level
predetermined to provide a predetermined thermal treatment of the
flowable biomaterial at a predetermined mass flow rate. These
variables can be predetermined by one of ordinary skill in the art
after a review of the present disclosure, depending of the
biomaterial of interest.
[0158] Continuing with reference to FIGS. 1, 9 and 10, apparatus 10
can comprise a packaging device PD for one of packaging flowable
preparation PR for refrigerated storage, aseptically packaging
flowable preparation PR, and both packaging flowable preparation PR
for refrigerated storage and aseptically packaging flowable
preparation PR. By way of example, packaging device of apparatus 10
can comprise a hold tube HT adapted for flow (or fluid)
communication with conduit 15, such as by conduit section 32; a
cooling unit CU adapted for flow (or fluid) communication with hold
tube HT, such as by conduit section 34; filling unit FU adapted for
flow (or fluid) communication with cooling unit CU, such as by
conduit section 36; and storage unit SU adapted for flow (or fluid)
communication with cooling unit CU, such as by conduit section 38.
Optionally, storage unit SU is a refrigerated storage unit.
Optionally, surfaces of hold tube HT, cooling unit CU, filling unit
FU, and storage unit SU that will contact preparation PR are
rendered commercially sterile prior to the introduction of flowable
preparation PR. Control device CD can provide appropriate control
signals for packaging device PD and components thereof. FIG. 15 is
a photograph showing the filling of sterile bag SB with a sweet
potato preparation SP, via a filling unit FU.
[0159] Referring now to FIGS. 13A-13C, a temperature sensor T1 is
disclosed. Temperature sensor T1 is used for measurement and
monitoring of cross-sectional temperature distributions.
Temperature sensor T1 can comprise combination of single or several
multi-point thermocouple probes TP providing cross-sectional
coverage of the area perpendicular to the direction of material
flow (see FIGS. 9 and 10). Temperature probes TP are operatively
connected to couplers CO, which are then in communication with
control device CD (see FIGS. 9 and 10). In the embodiment shown in
FIG. 13C, temperature sensor T1 further comprises a clamp assembly
CA that can be used to facilitate mounting of temperature sensor
T1. Positioning and utilizing such sensing and monitoring tools at
key locations (heater entry and exit and mixing element entry and
exit) has been used to test and document the uniformity and/or its
absence and illustrate the efficiency of a variety of mixing
implements and tools in achieving temperature equalization in
accordance with the presently disclosed subject matter.
[0160] FIGS. 14A and 14B are schematic diagrams of an exemplary
mixing device, referred to as M1''. Mixing device M1'' can provide
mechanical mixing effects in all previously listed target locations
(preceding, concurrent and/or subsequent to heating, see FIGS. 9
and 10) at the same time and using the same device. M1'' comprises
a mixing element, and mechanical mixing effects can be achieved by
extending the mixing element throughout these regions. The mixing
element is fabricated from a MW or RF-transparent material and
provides a concurrently rotating and orbiting movement within the
exposure region, ensuring that no configuration is static and
minimizing the likelihood of overheating and/or runaway heating
within the transparent tube or chamber.
[0161] With reference first to FIG. 14A, the material to be heated
A' enters the heating segment through a stainless steel
elbow-shaped tube 101, continues through a microwave transparent
tube segment 102 where it undergoes heating delivered by microwaves
using either a focusing structure of a microwave applicator or a
simpler microwave exposure region design 103, and mixing with a
single or multiple microwave-transparent polymer (such as but not
limited to TEFLON.RTM., polyether ether ketone (PEEK), polysulfone,
TPX.RTM. polymethylpentene (PMP), polycarbonate, or ULTEM.RTM.
polyetherimide) mixing elements 109. Material A' exits the
microwave exposure region and enters first the straight stainless
steel tube segment 104 containing the cylindrical ferromagnetic
mixer core 110 encased either in stainless steel or TEFLON.RTM..
The single or multiple mixing element(s) 109 are attached to the
bottom of the ferromagnetic core at the edge of its cylindrical
perimeter. A stainless steel spacer element 111 is attached to the
top of the cylindrical ferromagnetic core and maintains the
vertical position of the cylindrical core and the element taking
advantage of the upwardly moving push of the incoming material and
the centrifugal pulling force of one of the four to eight
externally radially-positioned electromagnets a-d. Electromagnets
a-d are switched on one at a time and the power is cycled (steps
1-6 are repeated continuously). Power and control can be provided
in any suitable manner, such as but not limited to through a
control device CD, as shown in FIGS. 9 and 10. This results in a
radial and rotational movement of ferromagnetic mixer core 110 and
a rotating as well as orbiting movement of single or multiple mixer
element(s) 109. This provides the mixing action within the
microwave exposure region without obstructing the focused microwave
energy distribution for any length of time at any individual point
along its path: the radial position of the mixing element(s) as
well as their position along the internal perimeter of the straight
stainless steel tube portion of the flow path constantly change.
The rate of the change of this position and therefore the rate of
mixing action can be controlled by increasing or decreasing the
speed of electromagnet switching steps 1 through 6. Cylindrical
ferromagnetic mixer core 110 as well as stainless steel spacer
element 111 provide additional mixing for the flowing material
which finally enters an elbow stainless steel tube element 105 and
exits the heating/mixing process segment A''. Optionally, single or
multiple temperature monitoring fixtures (e.g. temperature sensors
T1 et seq. as disclosed herein) can be used at the heater/mixer
entry 112a and the exit 112b locations to monitor and confirm the
achieved temperature increases and distributions.
[0162] Turning now to FIG. 14B, material to be heated A' enters the
heating segment through stainless steel elbow-shaped tube 101,
continues through microwave transparent tube segment 102 where it
undergoes heating delivered by microwaves using either a focusing
structure of a microwave applicator or a simpler microwave exposure
region design 103, and mixing with a single or multiple
microwave-transparent polymer (including but not limited to
TEFLON.RTM., polyether ether ketone (PEEK), polysulfone, TPX.RTM.
polymethylpentene (PMP) or ULTEM.RTM. polyetherimide) mixing
elements 109. The material exits the microwave exposure region and
enters first the straight stainless steel tube segment 104
containing the cylindrical ferromagnetic mixer core 110 encased
either in stainless steel or TEFLON.RTM.: the single or multiple
mixing element(s) 109 are attached to the bottom of the
ferromagnetic core at the edge of its cylindrical perimeter. A
stainless steel spacer element 111 is attached to the top of the
cylindrical ferromagnetic core and maintains the vertical position
of the cylindrical core and the element taking advantage of the
upwardly moving push of the incoming material and the centrifugal
pulling force of the externally positioned strong permanent magnet
108. Strong permanent magnet 108 is affixed to a perimeter of a
donut-shaped stage 107 which is driven to rotate around the
stainless steel tube through a sprocket, belt or clutch-friction
type interface with an electromotor-driven rotating element 106.
The orbiting motion of permanent magnet 108 results in a radial and
rotational movement of ferromagnetic mixer core 110 and a rotating
as well as orbiting movement of mixer element(s) 109. This provides
the mixing action within the microwave exposure region without
obstructing the focused microwave energy distribution for any
length of time at any individual point along its path: the radial
position of the mixing element(s) as well as their position along
the internal perimeter of the straight stainless steel tube portion
of the flow path constantly change. The rate of the change of this
position and therefore the rate of mixing action can be controlled
by increasing or decreasing the speed of electromagnet switching
steps 1 through 6. Cylindrical ferromagnetic mixer core 110 as well
as stainless steel spacer element 111 provide additional mixing for
the flowing material which finally enters elbow stainless steel
tube element 105 and exits the heating/mixing process segment A''.
Optionally, single or multiple temperature monitoring fixtures can
be used at heater/mixer entry 112a and exit 112b locations to
monitor and confirm the achieved temperature increases and
distributions.
[0163] III.B. Microwave and/or Radio Frequency Transparent
Tubes
[0164] The presently disclosed subject matter can employ a
composite integrated design for a microwave transparent composite
tube and a sanitary fitting that addresses heretofore known causes
of flow-through tube failures during microwave thermal processing
of foods, beverages, chemicals and biomaterials.
[0165] The advent of new microwave (MW) and other non-contact
heating (for example, radio frequency (RF)) technologies has
created a need for flow-through devices and assemblies that could
be used in these systems under conditions of relatively high
temperature and pressure, very high energy density and throughput
per unit area; high chemical and physical stresses ranging from
chemically aggressive processed material components to physical
stresses of high pressure, expansion, torsion and vibration and
impact.
[0166] The characteristics of a flow-through device or cavity to be
used for the continuous flow thermal treatment of foods, beverages,
chemicals, and other biomaterials can be numerous and highly
specific. They can be categorized into the following desirable
characteristics: [0167] 1. Extremely high microwave transparency
(very low value of dielectric loss factor and tangent) under
commonly occurring operational conditions [0168] 2. Capability to
withstand sterilization level temperatures without degradation or
property change [0169] 3. Capability to withstand sterilization
level pressures without degradation or property change [0170] 4.
Capability to withstand sterilization level temperatures at
sterilization level pressures without degradation or property
change [0171] 5. Capability to withstand chemically aggressive
components of processed materials without degradation or property
change [0172] 6. Capability to withstand dimensional, expansional,
thermal, vibrational and impact stresses regularly encountered
during the process without degradation or property change [0173] 7.
Compliance with FDA, USDA and pharmaceutical regulations for food
or other biomaterial-contact surface [0174] 8. Compliance with 3A
design requirements for in-place cleaning and sanitation
[0175] Additional characteristics that can appear in some
embodiments include the following:
[0176] 1. Visible light transparency or translucency--to identify
imperfections in material that could later lead to depositions
and/or failures--also to identify undesired boiling/flashing of the
processed material during the actual process and post-process
identification of deposits or defects caused during the run.
[0177] 2. High gloss, smooth and slick, non-stick, pinhole-free
material contact surface
[0178] 3. Capability for quick and easy insertion and removal from
the microwave or RF focusing structure
(radiator/concentrator/reactor/heater)
[0179] 4. Capability for integration into existing food, beverage,
chemical, and biomaterial processing lines (typically by using
standard aseptic interfacing components and standards, such as
tri-clamp or other sanitary types of fittings)
[0180] The lack of readily and commercially available devices that
would appropriately address some or all of these issues and
considerations has evolved into one the major hurdles in
implementing advanced microwave and RF technologies for continuous
thermal processing of foods, beverages, chemicals, and other
biomaterials.
[0181] Previously, four types of assemblies/tubes were
considered:
[0182] Type 1: Composite (three-piece) TEFLON.RTM. tubes consisting
of semi-transparent linear, extrusion-drawn TEFLON.RTM. tube piece
fitted at each end with a stainless steel crimp-on collar
fitting/sanitary interface (Tri-clamp). These assemblies have been
typically used as tank liquid-level view-ports for chemically
aggressive or high-temperature contents. The assemblies were
obtained commercially and subsequently tested in our labs and pilot
plants.
[0183] Type 2: Composite (three-piece) glass or ceramic tubes
consisting of a smooth-bore ceramic or glass tube fitted at each
end with a stainless steel screw-on or glue-on collar
fitting/sanitary interface (Tri-clamp). These assemblies have been
specifically fabricated according to microwave fabricator's orders
and specifications and subsequently tested in our pilot plants.
[0184] Type 3: Single piece glass or ceramic tubes consisting of a
smooth-bore ceramic or glass tube with machined or molded end
fittings comprising sanitary interfaces (Tri-clamp). These
assemblies have been specifically fabricated per microwave
fabricator's orders and specifications but have not been available
for testing.
[0185] Type 4: Single piece tubes consisting of a machined
smooth-surface advanced plastic tube with machined or molded end
fittings comprising sanitary interfaces (tri-clamp). These
assemblies have been specifically fabricated in the North Carolina
State University Instrument Shop according to chosen specifications
and have been thoroughly tested. Fabrication materials included
Ultem 1000 (polyetherimide), polysulphone, polymethylpentene (TPX),
and PEEK (polyetheretherketone), or other suitable
microwave-transparent polymers.
[0186] The following desirable characteristics were identified for
each of the four considered designs--failure modes are also
indicated for each type to further illustrate the need for an
appropriate alternative solution provided by the current
invention:
[0187] Type 1 [0188] Smooth, non-stick surface [0189] MW
transparency [0190] FDA, USDA, Pharma-compliant [0191] Readily
available on open market [0192] Temperature resistance [0193]
Resistance to most aggressive chemicals [0194] Typical failure
mode: pressure deformation at operating temperatures
[0195] Type 2 [0196] Smooth, non-stick surface [0197] MW
transparency [0198] FDA, USDA, Pharma-compliant [0199] Temperature
and pressure resistance [0200] Resistance to most aggressive
chemicals [0201] Typical failure modes: thermal stress fractures at
interface of steel and ceramic due to different thermal expansion
rates, impact fractures, and adhesive breakdown
[0202] Type 3 [0203] Smooth, non-stick surface [0204] FDA, USDA,
Pharma-compliant [0205] Temperature and pressure resistance [0206]
Resistance to most aggressive chemicals [0207] Anticipated failure
modes: thermal stress fractures, impact fractures
[0208] Type 4 [0209] Temperature and pressure resistance [0210]
Inexpensive, one piece design [0211] FDA, USDA, Pharma-compliant
[0212] Typical failure modes: material deposits due to non-smooth
surface, localized overheating at deposit locations, stress
fractures at weak interfaces (clamp fittings)
[0213] Referring now to FIGS. 11A-11E, a set of schematic views of
tubes are presented. Representative materials are generally shown
through the use of shading, which can be summarized as follows:
solid shading, crimp-on stainless steel sanitary fitting; gray
shading, PTFE/extruded PTFE; tight horizontal and vertical
cross-hatching, Ultem, polysulphone, or PEEK sleeve; diagonal
cross-hatching, MW-transparent high grade (alumia) ceramic; wide
horizontal lines, machined PTFE semi-cylinders; close horizontal
lines, multiple layers of thick PTFE film.
[0214] Referring now to FIGS. 11A and 11F, in some embodiments a
tube in accordance with the presently disclosed subject matter
comprises a constricting cylindrical sleeve OSL fabricated from
temperature and pressure resistant materials from Type 4 tube
assemblies (polyetherimide/Ultem, polysulphone, polymethylpentene
(TPX), or PEEK) overlaid over the pressure-susceptible TEFLON.RTM.
(or other smooth-surface compliant and microwave transparent
material) tube segment inner wall IW of assembly Type 1. This
design yields a smooth product-contact surface--TEFLON.RTM.,
thereby reducing the occurrence of product deposition failure, a
multi-fold increase in pressure resistance characteristics (Ultem,
polysulphone, polymethylpentene (TPX) or PEEK) and a high
resistance to stress fracture failures at sanitary interface points
SF (clamp fittings made of stainless steel). This would result in a
four-piece tube assembly (TEFLON.RTM. inner wall IW; Ultem,
polysulphone, polymethylpentene (TPX), or PEEK sleeve and two
crimp-on stainless steel sanitary clamp fittings SF).
[0215] Referring now FIG. 11B, in some embodiments a tube in
accordance with the presently disclosed subject matter comprises a
single-piece machined tube fabricated from one of the advanced
polymers used in the production of Type 4 tube assemblies (Ultem,
polysulphone, polymethylpentene (TPX), or PEEK) with the internal
bore surface IW coated with TEFLON.RTM. (or other smooth-surface
compliant and microwave transparent material) to provide the smooth
product contact surface. Such assembly could remain somewhat
susceptible to stress fractures at sanitary clamp interfaces, but
this is manageable with appropriate monitoring.
[0216] In addition to these representative embodiments, numerous
derivative designs can be assembled, for example, involving
additional microwave and/or radio frequency transparent (MWRFT)
layers or sleeves, alternative materials for crimped sanitary
fittings, and combinations of machined, extruded, and crimped
components.
[0217] Disclosed herein are representative MWRFT tube assemblies
with a smooth product-contact surface, thereby reducing the
occurrence of product deposition failures, a multi-fold increase in
pressure and physical resistance characteristics a high resistance
to stress fracture failures at sanitary interface points (clamp
fittings made of stainless steel). The representative tubes address
the high incidence of MWRFT flow-through tube assembly failure. A
high incidence of these failures is one of the hurdles to a wider
application of continuous-flow microwave heating/sterilization
technologies.
[0218] Referring now to FIGS. 11C and 11G, in some embodiments, the
MWRFT composite tubes employ a high-grade alumina ceramic sleeve
CSL as the external MWRFT layer, instead of a MWRFT high-grade
polymer. This layer can also provide pressure protection to the
internal extruded TEFLON.RTM. tube layer IW. FIGS. 11C and 11G
illustrate the components of a representative embodiment and an
exemplary assembly sequence for the same, including clamp fittings
SF, which optionally comprise stainless steel.
[0219] An embodiment of the MWRFT composite tube of FIGS. 11C and
11G has been constructed and experimentally tested under
semi-industrial production conditions (60 KW heater unit, 1-2
gal/min flow rate with temperature increases ranging from 100 to
140.degree. C.). This embodiment performed far better than any
other previously tested tube assembly. In one instance, the tube
was used for 14 consecutive runs yielding a total of greater than
50 hours of intermittent run time.
[0220] In previous testing, other tube assemblies often failed
after one or two uses. Furthermore, the tube failure modes
experienced with the assembly according to FIGS. 11C and 11G were
never catastrophic: i.e., these tubes never breached during a
processing run and no process materials escaped from the processing
system (as opposed to certain previous assemblies where leaks were
frequently caused by a variety of cracks, holes, and tears caused
by pressure, temperature, and deposit formation and/or
overheating).
[0221] However, even the tube assemblies of FIG. 11C eventually
failed after a period of use. Thus, monitoring of the period of use
is advisable. Tube failure can be caused by particle-containing
suspensions of processed materials, subsequent internal tube wall
deposits, overheating, and localized fouling of the internal tube
surface(s) and resulting flavor and/or color defects in the
processed material. The deposit formed on the internal surface of
the flow-through tube. If the deposit is severe enough and has been
subjected to extended overheating, the tube surface can be
permanently damaged rendering the tube assembly unusable. In some
instances, only one component of the assembly (the internal
extruded TEFLON.RTM. tube IW) failed, but the entire assembly often
needs to be discarded. Occasionally, external layer CSL of
high-grade ceramic alumina can be reused, but the cost of the
re-assembly with the new elements can be significant.
[0222] Tube failure can also be caused by cold shock upon heater
turn-off. In this case, the failure occurs when upon completion of
the heating run while both internal and external tube layers are
heated up to and above 130-140.degree. C., power to the MW heater
is switched off but the process pump continues to pump the cold
product through the tubing, causing the cold shock and cracking of
the external layer of the tube assembly at the top/hot end. Even
when only one of the components fails (e.g., the external ceramic
tube), the whole assembly typically needs to be discarded due to
the procedure used in the assembly.
[0223] Therefore two additional objectives for constructing
embodiments of the tube assembly are as follows: [0224] 1. Modify
the assembly sequence and process in order to simplify the removal
and replacement of one of the failed components as well as
re-assembly of the tube including the new replacement element(s)
[0225] 2. Thermally insulate the external ceramic tube layer in
order to protect it from overheating as well as the sudden cooling
caused by the power turn-off and the resulting immediate contact
with the process material at low temperatures
[0226] Both of these objectives have been met by the embodiments of
the presently disclosed subject matter depicted in FIGS. 11D and
11H, and FIGS. 11E and 11I. As shown in FIGS. 11D and 11H, a
pre-fabricated, commercially available three-piece extruded
TEFLON.RTM. sight-port IW was covered with a precision-machined
TEFLON.RTM. tube SC cut longitudinally along the length into two
identical semi-cylindrical pieces. The two halves were pressed
against the internal tube IW of TEFLON.RTM. as an external layer of
high-grade ceramic tubing CSL was pulled over the stainless steel
clamps SF and around the two tube halves SC comprising machined
TEFLON.RTM.. This ensured appropriate pressure and temperature
protection for the internal TEFLON.RTM. tube IW, thermal protection
to the external ceramic layer CSL as well as ease of assembly,
disassembly, and parts replacement for repeated use of undamaged
components.
[0227] FIGS. 11E and 11I illustrate another embodiment of the tube
assembly. A pre-fabricated, commercially available three-piece
extruded TEFLON.RTM. sight-port IW is covered by winding a thick
TEFLON.RTM. film FL around its external perimeter until the
external diameter of the tube and multiple film layers reaches a
thickness close to the external diameter of stainless steel clamps
SF. The wound layers of thick TEFLON.RTM. film FL are held pressed
against the internal tube IW of TEFLON.RTM. as an external layer of
high-grade ceramic tubing CSL is pulled over stainless steel clamps
SF and around the multiple layers of TEFLON.RTM. film FL. This also
ensures appropriate pressure and temperature protection for the
internal TEFLON.RTM. tube IW, thermal protection to the external
ceramic layer as well as ease of assembly, disassembly and parts
replacement for repeated use of undamaged components.
[0228] In addition to the embodiments specifically described
hereinabove, numerous derivative designs can be assembled, for
example, involving additional MWRFT layers or sleeves, alternative
materials for crimped sanitary fittings, and combinations of
machined, extruded, and crimped components.
[0229] Summarily, disclosed herein is a MWRFT tube assembly with a
smooth product-contact surface, thereby reducing the occurrence of
product deposition failures, a multi-fold increase in pressure and
physical resistance characteristics, and a high resistance to
stress fracture failures at sanitary interface points (clamp
fittings made of stainless steel). The disclosed tubes address the
high incidence of MWRFT flow-through tube assembly failures due to
a variety of factors. A high incidence of these failures is one of
the hurdles to a wider application of continuous-flow microwave
heating/sterilization technologies.
EXAMPLES
[0230] The following Examples have been included to illustrate
modes of the presently disclosed subject matter. Certain aspects of
the following Examples are described in terms of techniques and
procedures found or contemplated by the present co-inventors to
work well in the practice of the presently disclosed subject
matter. These Examples illustrate standard practices of the
co-inventors. In light of the present disclosure and the general
level of skill in the art, those of skill will appreciate that the
following Examples are intended to be exemplary only and that
numerous changes, modifications, and alterations can be employed
without departing from the scope of the presently disclosed subject
matter.
Example 1
Preparation of Sweetpotato Puree (SPP)
[0231] Beauregard cultivar sweetpotatoes were prepared in the Fruit
and Vegetable Pilot Plant, Department of Food Science, North
Carolina State University (Raleigh, N.C., United States of
America), for testing in a 5 kW microwave unit, color, and
rheological analyses, and measurement of dielectric properties. The
roots were cured at 30.degree. C. at 85-90% relative humidity for
seven days stored at 13-16.degree. C. and 80-90% relative humidity,
and the puree was prepared as previously described (Truong et al.
1994). Roots were washed, lye-peeled in boiling solution
(104.degree. C.) of 5.5% NaOH for 4 minutes, and thoroughly washed
in a rotary-reel sprayed washer to remove separated tissue and lye
residue. Peeled roots were hand-trimmed and cut into approximately
0.95 cm thick slices using a commercial slicer (Louis Allis Co.
Slicer, Milwaukee, Wis., United States of America). The slices were
steam-cooked for 20 minutes in a thermoscrew cooker (Rietz
Manufacturing Co., Santa Rosa, Calif., United States of America)
and comminuted in a hammer mill (Model D, Fitzpatrick Co., Chicago,
Ill., United States of America) fitted with a 0.15 cm screen. The
puree was filled into polyethylene bags, frozen and stored at
-20.degree. C. until used.
[0232] For test runs in a 60 kW microwave unit, frozen sweetpotato
puree from Beauregard cultivar was purchased from Bright Harvest
Sweetpotato Company, Inc. (Clarksville, Ark., United States of
America). All of the puree samples used in the Examples had
moisture contents of 80-82%.
Example 2
Measurement of Dielectric Properties
[0233] An open coaxial dielectric probe (HP 85070B; Agilent
Technologies, Palo Alto, Calif., United States of America) was used
with an automated network analyzer (HP 8753C; Agilent Technologies)
to measure the dielectric properties of the SPP samples. The
dielectric properties were measured in the 300 to 3000 MHz
frequency range, with 541 intermediate frequencies. The system was
calibrated using the calibration sequence following the instruction
manual provided by the manufacturer (Agilent 1998). The samples
(<100 g) were heated in a water bath (Model RTE111, Neslab
Instruments Inc, Newington, N.H., United States of America) until
the desired temperatures (10.degree. C. to 145.degree. C. in
5.degree. C. intervals) were attained, the samples were then placed
in an insulating block to measure the dielectric properties. The
temperature was measured again after the dielectric properties were
read to ensure that the temperature was within 2.degree. C. of the
set point. Three repetitive measurements were performed for each
duplicated samples.
Example 3
Rheological Tests
[0234] Constant rate measurement of sweetpotato puree viscosity as
a function of shear rate was performed at 25.degree. C. with a
StressTech rheometer (Reologica Instruments AB, Lund, Sweden) using
a cone and plate geometry (C40 4). Apparent viscosity was recorded
as shear rates were ramped from 0.1/s to 300/s. Two repeated
measurements were performed on each of the duplicated samples.
Example 4
Color Analysis
[0235] Objective colors of the samples were measured with a Hunter
colorimeter (Hunter Associates Laboratory Inc., Reston, Va., United
States of America). Results were expressed as tri-stimulus values:
L* (lightness, 0 for black, 100 for white); a* (-a*=greenness,
+a*=redness); and b* (-b=blueness, +b=yellowness. See CIE, 1976.
The instrument (45.degree./0.degree. geometry, D25 optical sensor)
was calibrated against a standard white reference tile (L*=92.75,
a*=-0.76, b*=-0.07). The puree samples were filled into a
60.times.15 mm covered Petri dishes (Becton Dickinson Labware,
Franklin Lakes, N.J., United States of America). Six measurements
were performed for each sample and average values were used in the
analysis.
Example 5
Tests in a 5 kW Microwave Unit
[0236] A continuous flow microwave-heating unit (Industrial
Microwave Systems, Morrisville, N.C., United States of America) was
used for processing SPP. The unit included a 5 kW microwave
generator operating at 915 MHz, a waveguide of rectangular
cross-section, in which a directional coupler was attached, and a
specially designed applicator. A tube of 1.5'' nominal diameter
(0.038 m ID) made of polytetrafluoroethylene (PTFE or TEFLON.RTM.)
was placed at the center of the applicator. The exposure region to
the microwaves was 0.125 m long. The power delivered by the
microwave generator and the power reflected back were measured
using diodes located in the directional coupler and a software
written in LabView software (National Instruments Corp, Austin
Tex., United States of America). This software also controls the
amount of power the generator delivers to the product.
[0237] Ten liters of SPP were pumped using a positive displacement
pump (Model MD012, Seepex GmbH+Co, Bottrop, Germany) at a rate of
0.5 L/min. Temperatures at various radial locations were measured
using a thermocouple arrangement described in Coronel et al. 2003
and recorded using a datalogger (Keithley DAS-16, Keithley
Metrabyte, Taunton, Mass., United States of America). The power of
the generator was adjusted using the control software to ensure
that the product attained the required centerline temperature at
the exit of the applicator. The product was then cooled in an
ice-water bath and samples were taken for further analysis.
Example 6
Test in the 60 kW Microwave Unit
[0238] Based on the results obtained in the tests in the 5 kW unit,
processing conditions were established for a test in a 60 kW
continuous flow microwave-heating unit (Industrial Microwave
Systems, North Carolina, United States of America) operating at 915
MHz (depicted in FIG. 12). The power delivered by the generator was
monitored by a control panel supplied by the manufacturer. The
microwaves were delivered to the product by a waveguide of
rectangular cross-section, which were split into two sections and
geared toward two specially designed applicators, with a
directional coupler in each as seen in FIG. 1. A PTFE tube (0.038 m
ID) was placed at the center of each applicator and the exposure
region was 0.2 m long in each applicator.
[0239] A positive displacement pump (Model A7000, Marlen Research
Corp., Overland Park, Kans., United States of America) was used to
pump the product through the system. Temperatures were measured at
the inlet of the system, the inlet and exit of each applicator, and
at the holding tube exit. Arrangements of the thermocouples were as
described by Coronel et al., 2003. The temperatures were recorded
at 4-second intervals using a Datalogging system (HP 3497A, Hewlett
Packard, Palo Alto Calif., United States of America). The
temperature at the exit of the system was achieved by controlling
the power generated by the microwave system.
[0240] The system was first sterilized using an aqueous solution of
NaCl and sugar, which was heated to 130.degree. C. and recirculated
for 30 minutes. The product was heated to 135-145.degree. C., held
for 30 seconds, rapidly cooled in a tubular heat exchanger, and
then aseptically packaged in aluminum-polyethylene laminated bags
(Scholle Corp, Chicago, Ill., United States of America) using a
bag-in-box unit (Model PT.A.F., Astepo, Parma, Italy). The puree
bags were stored at ambient temperature (22.degree. C.) and two
bags were randomly taken for microbiological analysis after 1, 15,
and 90 days. A standard plate count assay was used to enumerate
total aerobic bacteria in the sweetpotato puree samples. Fifty gram
samples were aseptically transferred to sterile filter bags (Spiral
Biotech, Bethesda, Md., United States of America) containing 50 ml
of sterile physiological saline solution (0.85% NaCl), and the bags
were macerated with a Tekmar stomacher (Model TR5T, Tekmar Co.,
Cincinnati, Ohio, United States of America) on high speed for 160
seconds. Appropriate dilutions of the stomacher filtrate were made
using sterile physiological saline solution and spread onto
duplicate PCA agar plates using an Autoplate 4000 spiral plater
(Spiral Biotech). The PCA plates were inoculated and grown at
37.degree. C. for 48 hours for total aerobic bacterial counts.
Sample dilutions were also spread onto plates of yeast/mold agar
plates and inoculated for enumeration of yeast and mold colonies.
Medium preparation was carried out following standard procedures
(DIFCO, 1998).
[0241] Data were subjected to the analysis of variance (SAS
Institute, Cary, N.C., United States of America). Statistical
testing was performed at the 95% (p<0.05) confidence level.
Discussion of Examples 1-6
[0242] Dielectric Properties. The dielectric properties of the
sweetpotato puree disclosed herein were compared to those reported
by Fasina et al., 2003 and shown in FIG. 2. The correlations for
dielectric properties provided in Fasina et al. 2003 were in good
agreement with the measured values of .di-elect cons.' (dielectric
constant) and .di-elect cons.'' (loss factor). The differences were
more noticeable in the values of .di-elect cons.'', which is likely
a result of compositional and moisture variations observed in
agricultural products (Sipahioglu and Barringer, 2003). The effect
of temperature on the dielectric constant was similar for both 915
and 2450 MHz, with .di-elect cons.' decreasing with an increase in
temperature, with values of 71.5 at 10.degree. C. and 60.8 at
95.degree. C. for 915 MHz, and with values of 67.1 at 10.degree. C.
and 61.1 at 95.degree. C. for 2450 MHz. The loss factors followed a
trend of increased .di-elect cons.'' with increasing temperature,
with values of 18.1 at 10.degree. C. and 26.7 at 95.degree. C. for
915 MHz. However, at 2450 MHz .di-elect cons.'' decreased with an
increase in temperature with values of 18.4 at 10.degree. C. and
16.1 at 95.degree. C.
[0243] The maximum operating diameter (MOD) of the tube to be used
in the applicator was calculated using the method proposed by
Coronel & Simunovic, 2004 that involves a solution of the
Helmholtz equation in cylindrical coordinates, and the results are
shown in FIG. 3. Briefly, the penetration depth of the microwaves
was calculated by solving the penetration equation in cylindrical
coordinates considering a constant E field in the outside of a
cylinder with a diameter of 38 mm (1.5 inches). The differential
equation was a Helmholtz type equation:
.gradient..sup.2E+.gamma..sup.2E=0 .gamma.=.alpha.+j.beta. B.C. r=R
E=E.sub.0
[0244] Where .gamma. is the propagation constant and .alpha. and
.beta. are defined as: .alpha. = .omega. .times. .mu. .times.
.times. 2 .function. [ 1 + [ .sigma. .omega. .times. .times. ] 2 -
1 ] ##EQU1## .beta. - .omega. .times. .mu. .times. .times. 2
.function. [ 1 + [ .sigma. .omega. .times. .times. ] 2 + 1 ]
##EQU1.2##
[0245] The solutions to this equation were given by Bessel
functions in the form:
E(r)=C.sub.1J.sub.0(.gamma.r)+C.sub.2Y.sub.0(.gamma.r)
[0246] The value of the constants depended on the dielectric
properties of the material and dimensions of the tube. The MOD was
considered the diameter in which: E.sub.r=0/E.sub.0=1.
[0247] Thus, the maximum operating diameter (MOD) was defined as
the maximum diameter that can be used in continuous flow processing
to obtain the necessary heating across the cross-sectional area,
and it was calculated at different temperatures. It can be observed
that MOD decreases with temperature with values of 0.22 m at
10.degree. C. and 0.12 m at 95.degree. C. for 915 MHz. The increase
in the loss factor with temperature makes energy conversion into
heat more effective, thus decreasing the penetration depth and
hence, the M.O.D. (see FIG. 3)
[0248] Tests in a 5 kW Microwave Unit. The product was processed
using the 5 kW microwave unit, keeping a constant holding time and
changing the centerline exit temperature. The desired centerline
exit temperatures were 110, 130, and 140.degree. C. with an
exposure time in the heating section of 17 seconds and a holding
time of 90 seconds. The product was cooled rapidly in an ice-water
bath and samples were taken for analysis of the rheological
properties and color.
[0249] Large temperature differences were observed between the
walls and the center of the applicator tube. The differences
between the maxima and minima were 35, 40, and 43.degree. C. for
centerline exit temperatures of 110, 130, and 140.degree. C.
respectively with average exit temperatures of 80, 101, and
107.degree. C. respectively. FIG. 4 shows the interpolated
temperature profiles in the cross section of the tube at the exit
of the heating section for the exit temperatures of 110 and
130.degree. C. It can be observed in FIG. 4 that the highest
temperature is achieved close to the center of the tube, and the
minimum close to the walls.
[0250] The rheological properties of the samples treated to
different centerline exit temperatures are shown in FIG. 5. All the
samples exhibited shear-thinning behavior (i.e., lower apparent
viscosity at higher shear rates). The rheological behavior was
modeled using a Herschel-Bulkley model
(.sigma.=.sigma..sub.0+K.gamma..sup.n), wherein .sigma. is sheer
stress (Pa), .sigma..sub.0 is yield stress, K is the consistency
index (Pa s.sup.n), .gamma. is the shear rate (1/s), and n is the
flow behavior index as described in Steffe, 1996. The average
values of the parameters were: yield stress (.sigma..sub.n)
89.01.+-.2.67 Pa, the consistency index (K) 18.78.+-.1.76 Pa, and
the average flow behavior index (n) 0.39.+-.0.07. In FIG. 5 it can
be seen that the apparent viscosity of the different SPP samples
did not show significant differences between treatments.
[0251] Color measurements of the samples corresponding to different
centerline exit temperatures are shown in FIG. 6. All the samples
presented an increase in b* value (yellowness; 5% for the
110.degree. C. treatment and by 10% for the 130.degree. C. and
140.degree. C. treatments) and a decrease in a* value (redness; 9%
for the 110.degree. C. treatment, and 10.5% for the 130.degree. C.
and 140.degree. C. treatments), while the L* value (lightness)
remained changed 2% for all treatments. The total change in color
(.DELTA.E) is expressed as the result of the following equation:
.DELTA.E=(.DELTA.L*.sup.2+.DELTA.a*.sup.2+.DELTA.b*.sup.2).sup.1/2
.DELTA.E values were 10, 20, and 20 for centerline exit
temperatures of 110, 130, and 140.degree. C., respectively.
[0252] Tests in a 60 kW Microwave Unit. With the information
gathered from the tests on 5 kW microwave unit, the test runs using
the 60 kW unit were carried out as a pilot plant experiment aiming
to obtain a shelf-stable product. The flow rate was set to 4.0
L/min, and in order to obtain a shelf-stable product the centerline
temperature at the exit of the holding tube required was
135.degree. C. with a holding time of 30 seconds (F.sub.o<30
minutes). The power generated by the system was adjusted in order
to achieve the required centerline exit temperature.
[0253] As observed in the 5 kW tests, the temperature differences
between the centerline (135.degree. C.) and the walls (70.degree.
C.) of the tube were large, as shown in FIG. 7. Because of the high
viscosity of the SPP no mixing occurred in the holding tube.
Therefore, the product closer to the walls was that which received
the least thermal treatment with (F.sub.o<0.1 minute). However,
the product was kept refrigerated and no microbial growth was
detected after 30 days.
[0254] In order to minimize the non-uniformity in temperature
within the product, static mixers were implemented at the exit of
each of the microwave applicators of the system. The mixing at the
exit of the heaters would diminish any temperature differences
within the product at the exit of the heaters in order to improve
the thermal treatment and in consequently the shelf life of the
product. The second experiment was carried out with centerline exit
temperature of 140.degree. C. at the exit of the second heater, and
a holding time of 30 seconds. The centerline temperature was
increased in order to achieve a minimum temperature of 135.degree.
C. at the end of the holding tube.
[0255] Temperatures throughout the cross-sectional area were more
uniform due to the mixing of the product. The temperature
differences between center and wall were reduced from 48.4 to
20.1.degree. C. after the first static mixer and from 37.6 to
11.7.degree. C. after the second static mixer. At the inlet of the
holding tube, SPP had a temperature profile as shown in FIG. 8,
with a minimum temperature of 135.degree. C. and a maximum of
146.7.degree. C. Thus, the fastest particle (at the center of the
tube) received the least heat treatment. The fastest fluid elements
(center) received a thermal treatment equivalent to F.sub.o=23
minutes, which rendered a commercially sterile product, which
should be shelf stable. Microbiological tests of the final product
were performed in order to confirm the destruction of
microorganisms. Microbiological test results on total plate count,
molds, and yeast showed no presence of microorganisms after 1, 15,
and 90 days.
[0256] Conclusions. Aseptically packaged sweetpotato puree was
successfully produced using a continuous flow microwave heating
system. The resulting product packed in flexible plastic containers
had the color and apparent viscosity comparable to the untreated
puree, and was shelf-stable. This process can be applied to several
other vegetable and fruit purees.
Example 7
Effect of Mixers on Temperature Equalization
[0257] SPP was treated in the 60 kW unit as described hereinabove,
and the temperature of the material was tested using thermocouples
at the exit of the first and second heaters in the absence of any
mixing devices. FIGS. 17 and 19 depict the wide variation in heat
across the cross section of the flow. The need for a mixing
implement subsequent to the heating stage is thus illustrated by
temperature distribution measurements and proven by the
unsuccessful sterilization results in preceding runs (without the
mixing stage).
[0258] Static mixers were then installed and the experiment
repeated. FIGS. 18 and 20 depict the temperature equalization
across the cross section of the flow as shown by the much narrower
temperature distribution.
[0259] These experiments were repeated using a white potato puree
(i.e., mashed potatoes). FIGS. 22 and 24 depict the temperature
distribution at the exit of the first and second heaters in the
absence of any mixing devices, and FIGS. 23 and 25 depict the
temperature equalization across the cross section of the flow as
shown by the much narrower temperature distribution.
Example 8
Treatment of Green Pea, Carrot, and White Potato Purees
[0260] Sample preparation. Frozen green peas and carrot purees were
purchased from Stahlbush Island Farm Inc. (Corvallis, Oreg., United
States of America). Refrigerated mashed potatoes were obtained from
Reser's Fine Foods (Beaverton, Oreg., Unites State of America) and
made into a purple colored puree by adding 300 grams of anthocyanin
solution (San Red YM-EX, San-Ei Gen F. F. I. Inc., N.J., United
States of America) and 7.5 liters of water per 150 pounds of mashed
potato. The materials were thoroughly mixed using a high shear
mixer (Rotosolver Mixer model 112RS113 with a Baldor 7.5 HP, 1725
rpm motor controlled by a Woods Model WFC2007-5CHT AC Inverter from
Admix, Manchester, N.H., United States of America).
[0261] The green pea and carrot purees were passed through a 5 kW
microwave unit as described in Example 5. The power of the
generator was adjusted using the control software to attain the
centerline temperature of the product at 75.degree. C., 100.degree.
C., 110.degree. C., 120.degree. C., 125.degree. C. and 130.degree.
C. at the exit of the applicator. Samples of the microwave-heated
purees were collected and immediately cooled in an ice-water bath,
and then stored at 4.degree. C. for further analysis within 3-4
days.
[0262] With the 60 kW microwave unit, these vegetable purees (green
peas, carrots, and potatoes) were processed as described in Example
6, except that the system was not connected to an aseptic filler.
The microwave-heated purees were continuously re-circulated for 6
hrs in the 60 kW system with a centerline exit temperature of
125-130.degree. C. Samples were taken at time intervals,
immediately cooled, and stored at 4.degree. C. for further
analysis.
[0263] Rheological tests. Dynamic rheological test was conducted
using a StressTech rheometer (Reologica Instruments AB, Lund,
Sweden) with 20 mm parallel plate geometry at 25.degree. C. Puree
samples were transferred onto the plate of the rheometer. The upper
plate was lowered onto the gel to a gap of 1.5 mm and excess
material was trimmed from the periphery. After the sample was
equilibrated at 25.degree. C. on the plate for 1 minute, small
strain oscillatory testing was carried out at 25.degree. C. The
sample was subjected to oscillatory sweep at a frequency range from
0.01 to 20 Hz. The oscillatory stress was set at 2 Pa, which was
within the linear viscoelastic region of the tested purees. The
storage modulus G', loss modulus G'', and dynamic viscosity .eta.*
were examined. Two repeated measurements were performed on each
puree sample.
[0264] Color Analysis. Color analysis was performed as described in
Example 4.
Discussion of Example 8
[0265] Carrot puree. The rheological properties of carrot puree
samples processed at various temperatures in the 5 kW microwave
unit are shown in FIGS. 26A and 26B. The dynamic viscosity (.eta.*)
of all carrot puree samples decreased with increasing frequency
(FIG. 26A), showing pseudoplastic behavior. The mechanical spectra
of carrot puree exhibited frequency dependency (FIG. 26B) with G'
higher than G'', indicating that the material can be classified as
weak gels. Increasing the microwaving temperature from 75.degree.
C. to 130.degree. C. resulted in a slight increase in the dynamic
viscosity of carrot puree.
[0266] The effect of microwaving temperature was more manifested in
gel strength (G') values (FIG. 26B). This phenomenon might be
attributable to the dissociation of bound carbohydrate components
of the cell debris into the liquid fraction of the puree resulting
in more network formation upon cooling. This effect of microwaving
temperature in flow behavior and gelling properties of carrot puree
can be beneficial to the processors if a product with slightly
increased consistency would be desirable. In any circumstance
wherein the puree viscosity and gel strength should be maintained
as that of the unheated puree, adjusting the water level in the
puree prior to microwave processing can be easily carried out.
[0267] Prolonging the microwaving time at 130.degree. C. by
re-circulating the carrot puree in 60 kW unit resulted in
disrupting the bonding and gel networks as indicated by significant
decreases in both .eta.* and G' (FIGS. 27A and 27B). Severe
disruptions of the consistency and gel strength of the carrot puree
were observed with heating time beyond 30 minutes. The results
demonstrated a severe quality loss of carrot puree subjected to the
high temperature and long time process required in conventional
thermal processing of vegetable purees.
[0268] Green pea puree. The rheological properties of green pea
puree samples processed at various temperatures in the 5 kW
microwave unit are shown in FIG. 28. The dynamic viscosity (.eta.*)
of all green pea puree samples also decreased with increasing
frequency (FIG. 28A), showing pseudoplastic behavior. The green pea
puree can be considered a weak gel since its mechanical spectra
exhibited frequency dependency (FIG. 28B) with G' higher than
G''.
[0269] In contrast to carrot puree, .eta.* and G' of the green pea
puree initially decreased upon heating to 75-110.degree. C., as
compared to the unheated sample, and then significantly increased
at higher temperatures (120-130.degree. C.). This trend was also
exhibited among the samples collected from the 60 kW unit
experiments wherein the green peas puree was heated up to
125.degree. C. and re-circulated for 6 hrs (FIG. 29). The
phenomenon could be attributed to the high amylose content (35%) of
pea starch and its C-type granular structure with high
crystallinity and a tight molecular architecture (Bogracheva et
al., 1998), which require high energy inputs for gelatinization and
melting. A fast heating-high temperature process as the microwaving
technique described herein would be beneficial in processing the
pea purees into products with desired consistencies and gel
properties.
[0270] The color of the green peas samples collected from the 60 kW
tests was also determined. As indicated in FIG. 30, the L* value
(lightness) and the b* value (yellowness) were slightly affected by
microwaving temperature and time (<5% decreases). However, the
loss in green color (a* values) was about 30% with reference to the
unheated sample for the green peas puree heated to 125.degree. C.
With increasing heating time at 125.degree. C. as in conventional
thermal processing, the green color (a* values) of the puree was
further degraded by 38% as compared to the unheated samples.
Example 9
Shelf Stability of Microwaved SP Purees
[0271] Frozen sweetpotato puree from Beauregard cultivar was
purchased from Bright Harvest Sweetpotato Company, Inc.
(Clarksville, Ark., United States of America). The thawed puree was
sterilized using the 60 kW unit and aseptically packaged as
described in Example 6. Packages of aseptic sweetpotato puree were
stored at ambient temperature (22.degree. C.), and two bags were
randomly taken for microbiological analysis after 1 day, 2 weeks, 3
months, 6 months, and 18 months. Standard plate count assays were
used to enumerate total aerobic bacteria, yeasts, and molds in the
sweetpotato puree samples (Example 6). Microbiological test results
for total aerobic bacteria, yeasts, and molds showed no growth of
microorganisms for the puree samples stored for 1 day, 2 weeks, 3
months, 6 months, or 18 months at 22.degree. C.
[0272] Rheological tests & Hunter color measurements were
performed as described in Example 8 for green pea and carrot
purees. As indicated in FIG. 31, microwave processing of
sweetpotato puree to 130.degree. C. and storing the aseptic
packages at ambient conditions had no effect on the rheological
properties of the puree. The stored samples retained the dynamic
viscosity and (.eta.*) and gel strength (G') comparable to those of
the frozen stored puree.
[0273] Color values of the microwaved sweetpotato puree as compared
to frozen and canned purees (canned sweetpotato puree (can size no.
10) purchased directly from a local sweetpotato cannery: Bruce
Foods Corporation, Wilson, N.C., United States of America) are
shown in FIG. 32. Microwave processing resulted an increase of 25%
in b* value (yellowness), slight decreases in a* (redness; <1%)
and L* values (lightness; <2%), as compared to the frozen puree.
Storage of the aseptic puree for 3 months at 22.degree. C. further
decreased the a* and L* values by 2.2% and 4.5%, respectively,
while the b* value was about 15% higher than that of the frozen
puree. The canned puree had dark brown color with L* values about
10.5% and 7.5% lower than those of the frozen puree.
Example 10
Color Degradation Data and Projections
[0274] In order to illustrate certain advantages of the rapid
heating methods and apparatuses disclosed herein, a series of
experimental measurements of the most sensitive of quality
attributes of these products--color were performed.
[0275] Color is the first quality attribute evident to the
industrial user, chef, cook and/or consumer available for
evaluation upon opening of the package. It is also one of the most
process-sensitive attributes for many of the targeted materials
(vegetable and fruit purees, homogenates and pulps). This
sensitivity is demonstrated by a rapid degradation of color
attributes when the target food or biomaterial is exposed to heat
at processing-level temperatures. The color, as evaluated by
sensory means (human vision) and instrumental means (color
measurements) undergoes rapid and often severe degradation upon
processing and subsequently during storage, both in hermetically
sealed and opened forms.
[0276] In order to measure the color degradation at temperature
levels representative of temperatures of exposure during
conventional aseptic and rapid microwave--assisted thermal
sterilization--and to clearly document the advantage provided by
the rapidity of thermal treatment achieved using the unique
cylindrical microwave heater devices under the conditions disclosed
herein and in combination with devices and procedures disclosed
herein, a novel method of color measurement, recording and
comparison have been devised.
[0277] The schematic of the high-temperature color degradation
assembly is presented in FIG. 38. The left-hand part of FIG. 38
shows the image and temperature control and acquisition
installation and the right-hand side of FIG. 38 shows the
components used to construct the image acquisition port enabling
the acquisition of images and measurement of color values of tested
materials in real time and under process-level temperatures.
[0278] A circulating oil bath with a digitally-controllable
temperature level (Model RTE 111, Neslab Inc., Newington, N.H.,
USA) was used to preheat the test chamber containing the target
material to selected process-level temperatures. The temperature
level most representative of actual operating conditions (target
temperatures) of both conventional continuous flow aseptic systems
as well as the microwave-assisted aseptic sterilization system
presented by this application is approximately 140.degree. C. The
oil bath system was therefore preheated to a level of 140.degree.
C. prior to submersing the test chamber containing the sample into
the preheated oil bath.
[0279] The experimental setup described above is also presented by
FIG. 39 and FIG. 40.
[0280] The test chamber to hold a minimally small quantity of
sample (in order to ensure rapid pre-heating) was assembled from a
1.5 inch diameter Smart Gasket (Model G-TH-150-S-1, Rubber Fab,
Andover, N.J., USA); which established the volume of the material
contained within the test chamber. The gasket was fitted with a
hypodermic three-point thermocouple probe (Model MT-23/20(3),
Physitemp Instruments, Inc., Clifton, N.J., USA) containing three
type T thermocouple leads within a 6 mm space at the tip of the
probe, placed in direct contact with the test material itself. The
bottom of the chamber was formed by using a 1.5 inch stainless
steel sanitary cap with a Tri-clamp gasket groove (Model
16AMP-2-1.5-T316L, Waukesha Cherry-Burrell, Delavan, Wis., USA);
whereas the top was fitted with a transparent view port made of
fused high temperature glass and steel (Model Fuseview
SS-15-FVTR1-FL, J.M. Canty Ltd, Dublin, Ireland) with the diameter
of the visible window fitted to the diameter of the contained
sample.
[0281] Temperatures acquired using the three-point thermocouple
probe were measured using a 12-channel scanning thermometer (Model
692-000, Barnant Company, Barrington, Ill., USA), acquired every 4
seconds and recorded using a serial-port connection of a generic
laptop computer. The typical image acquired by the system is
presented in FIG. 40. The image shows the sample chamber assembly,
special tri-clamp with a Smart gasket port containing the 3-point
thermocouple probe in contact with the sample material. The 256*256
pixel sub-sample has been painted white to illustrate the imaged
part of the sample surface that has been used in the color
degradation analyses.
[0282] The visible window of the sample chamber was positioned
facing up so that the timed images of the target material could be
captured using a digital camera (Model D70, Nikon Instruments,
Melville, N.Y., USA) every 4 seconds. The images were captured in a
raw/digital format uncompressed (Nikon Electronic Format),
converted into Adobe Photoshop readable TIF file format without
file compression, imported into Adobe Photoshop software version
5.5. and cropped to contain a 256*256 pixel array of exposed target
material. The average color values of L, a, and b of these reduced
sub-images were measured using the Photoshop Histogram Function.
The obtained values were then plotted against time of exposure of
the chamber to the temperature of 140.degree. C. using the Chart
function of Microsoft Excel Program (Microsoft Office 2000 Software
package) to plot the values of color components L, a and b versus
time of exposure to process temperature.
[0283] Microsoft Excel Chart function Trendline was used to
generate the linear regression lines and projected degradation of
color components (L, a* and b*) over time of exposure to
140.degree. C. Recorded worst case times of exposure for preheating
for the presented process as well as the hold times for the rapid
MW-based process were compared with the calculated estimates for
the worst-case type of exposure for the conventional aseptic
preheating (product pumped through approx. 200 feet of 1.5 inch
internal diameter tube in tube heat exchanger at 1 gallon per
minute flow rate). Identical hold time and temperatures were
assumed for either process (MW-based and conventional
preheating).
[0284] FIGS. 33-36 illustrate the results of real-time color
degradation measurements performed using the equipment and
methodology described above at 140.degree. C. temperature of oil
bath preheating.
[0285] On each of FIGS. 33-36 (Green Pea Puree, Carrot Puree, White
Potato Puree colored with Anthocyanin and Sweet Potato Puree) there
are five reference color quality/time of processing marked: Raw
Material (prior to processing), MW Preheated Material (exiting from
the MW heaters and in-line mixers), MW Sterilized Material (exiting
from the hold tube segment); conventionally pre-heated (exiting
from a typical tube in tube heat exchanger) and conventionally
sterilized (exiting from a hold tube after the preheating using
conventional heat exchangers).
[0286] For all four tested and illustrated materials, it is clearly
evident that color degradation commences instantaneously and
proceeds rapidly at a significant rate at sterilization level
temperatures. The advantage of implemented rapid heating using the
proposed MW or RF energy sources is also clearly evident from these
plots.
[0287] It can be stated that color quality of the material
subjected to a rapid MW or RF preheating is minimally degraded and
appears to be nearly identical to the original raw material. The
time required to hold the product at the final sterilization
temperature ads a slight degradative effect to the color quality;
however when compared to the worst case scenario for conventional
aseptic preheating and holding, both of these degradative changes
are minimal.
[0288] An advantage of rapid heating using the presently disclosed
subject matter is evident regardless of the initial quality of the
processed material--i.e. the damage imparted to the color quality
of the material by conventional preheating will always be
significantly greater than the degradation caused by rapid
heating--assuming that the time-temperature exposures during the
holding segment are identical, the difference between the two
cumulative treatments is demonstrably and consistently in favor of
the rapid MW/RF heating described herein.
[0289] In other words, the color quality of the product preserved
by the proposed MW/RF based treatment at the time of packaging
(time zero) will be superior to a conventionally treated
product.
[0290] Quality degradation in general, as well as color quality
degradation specifically, will continue to proceed during the
storage of the packaged products. The rate and extent of these
degradative processes will generally depend on conditions of
storage and transportation prior to opening. Therefore, if both
MW/RF sterilized and conventionally aseptically sterilized products
are subjected to an identical set of post-packaging storage,
transportation and distribution conditions; MW/RF sterilized
product will have a consistent quality advantage, since the
original color quality component will have been preserved to a much
greater extent at the time of packaging.
[0291] Therefore, under identical up-stream conditions (quality,
exposure and abuse history of the raw material) and identical
down-stream conditions (storage, transportation and distribution);
product obtained by the described MW/RF sterilization method will
have superior quality relative to the product obtained by
conventional thermal sterilization regardless and independent of
these conditions.
REFERENCES
[0292] The references listed below as well as all references,
including patents and non-patent literature, cited in the
specification are incorporated herein by reference to the extent
that they supplement, explain, provide a background for, or teach
methodology, techniques, and/or compositions employed herein.
[0293] Adey (1989) Biological effects of radio frequency
electromagnetic radiation, In: Electromagnetic Interaction with
Biological Systems (Lin (ed.)) Plenum Press, New York, N.Y., United
States of America, pages 109-140. [0294] Bogracheva et al. (1998)
45 Biopolymers 323-332. [0295] Campanella & Pelegi (1987) 52 J
Food Sci 214-217. [0296] Charm (1962) 28 J Food Sci 107-113. [0297]
CIE (1976). Colorimetry: official recommendations of the
International Commission on Illumination. Paris: Commission
Internationale de l' clairage [International Commission on
Illumination], CIE No. 15 (E-1.3.1). [0298] Coronel & Simunovic
(2004) Solution of Helmholtz equation to determine the feasibility
of continuous flow microwave processing of food materials. Under
review. [0299] Coronel et al. (2003) 68 Journal of Food Science.
1976-1981. [0300] Coronel et al. (2004) Dielectric properties of
pumpable food materials at 915 MHz. Submitted to Journal of Food
Science. Under review. [0301] De Kee et al. (1980) 10 J Texture
Stud 281-288. [0302] DIFCO (1998) Difco Manual, 11th edition. Difco
Laboratories, Division of Becton Dickinson and Company, Sparks,
Md., United States of America. [0303] Fasina et al. (2003) 6
International Journal of Food Properties. 461-472 [0304] Goldblith
(1975) In: Freeze Drying and Advanced Food Technology (Goldblith,
Rey and Rothmayr (eds.)), Academic Press, New York, N.Y., United
States of America, pages 691-714. [0305] Kyereme et al. (1999) 22
Journal of Food Process Engineering 235-247. [0306] Lopez, A.
(1987) A complete course in cannning and related processes. Book,
III. Processing procedure for canned products. Baltimore, Mass. The
Canning Trade. p. 96. [0307] Missaire et al. (1990) 21 J Texture
Stud 479-490. [0308] Nakayama et al., (1980) 45 J Food Sci 844-847.
[0309] Ofoli et al. (1987) 18 J Texture Stud 213-230. [0310] PCT
International Patent Application Publications WO 0036879, WO
0143508, and WO 0184889. [0311] Qui & Rao (1988) 53 J Food Sci
1165-1170. [0312] Sipahioglu & Barringer (2003) 68 Journal of
Food Science 234-239. [0313] Smith et al. (1982) 46 Journal of Food
Science 1130-1142. [0314] Steffe (1996) Rheological Methods in Food
Process Engineering, Second Edition. Freeman Press, East Lansing,
Mich., United States of America. [0315] Swartzel (1982) 47 Journal
of Food Science 1886-1891. [0316] Swartzel (1986) 34 Journal of
Agricultural and Food Chemistry 397. [0317] Toledo et al. (1977) 42
J Food Sci 725-727. [0318] Truong et al. (1995) 60 Journal of Food
Science 1054-1059, 1074. [0319] Truong (1992) In: Hill W A, Bonsi C
K and Loretan P A (Eds.). Sweetpotato Technology for the 21st
Century. Proceedings of the International Symposium, Jun. 2-6,
1991, Tuskegee, Ala., pages 389-399. [0320] Turner & Danner
(1957) Alabama Agricultural Experimental Station Circular No. 21.
[0321] U.S. Patent Application Publication Nos. 20010035407 and
20030205576 [0322] U.S. Pat. Nos. 4,091,119; 4,808,425; 4,975,246;
5,998,774; 6,087,642; 6,121,594; 6,265,702; 6,406,727; 6,583,395;
and 6,797,929 [0323] Woolfe (1992) Sweet potato: an untapped food
resource. Cambridge University Press, Cambridge, United
Kingdom.
[0324] It will be understood that various details of the presently
disclosed subject matter can be changed without departing from the
scope of the presently disclosed subject matter. Furthermore, the
foregoing description is for the purpose of illustration only, and
not for the purpose of limitation.
* * * * *