U.S. patent application number 10/843679 was filed with the patent office on 2005-06-09 for method for reduction of tobacco specific nitrosamines.
This patent application is currently assigned to PHILIP MORRIS USA INC.. Invention is credited to Bokelman, Gordon H., Hempfling, Walter P., Shulleeta, Maria.
Application Number | 20050121046 10/843679 |
Document ID | / |
Family ID | 32510909 |
Filed Date | 2005-06-09 |
United States Patent
Application |
20050121046 |
Kind Code |
A1 |
Hempfling, Walter P. ; et
al. |
June 9, 2005 |
Method for reduction of tobacco specific nitrosamines
Abstract
Tobacco is treated before or during curing to lower or eliminate
bacterial populations and/or activity, fungal growth, and/or
tobacco-specific nitrosamine or bacterial endotoxin levels in the
cured tobacco, wherein the tobacco is treated with an effective
amount of a wash solution. Air-cured tobacco may be cured in four
weeks or less when treated with a wash solution of bicarbonate
salts.
Inventors: |
Hempfling, Walter P.;
(Mechanicsville, VA) ; Bokelman, Gordon H.;
(Chesterfield, VA) ; Shulleeta, Maria; (Richmond,
VA) |
Correspondence
Address: |
BURNS DOANE SWECKER & MATHIS L L P
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
PHILIP MORRIS USA INC.
|
Family ID: |
32510909 |
Appl. No.: |
10/843679 |
Filed: |
May 12, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10843679 |
May 12, 2004 |
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09714105 |
Nov 17, 2000 |
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6755200 |
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60166413 |
Nov 19, 1999 |
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Current U.S.
Class: |
131/347 ;
131/300; 131/364 |
Current CPC
Class: |
A24B 15/183 20130101;
A24B 15/287 20130101; A24B 15/28 20130101; A24B 15/245
20130101 |
Class at
Publication: |
131/347 ;
131/364; 131/300 |
International
Class: |
A24B 001/02 |
Claims
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28. A cured tobacco leaf in a condition of having been contacted
with a wash solution comprising a disinfectant and a solvent such
that said leaf is with a reduced amount of tobacco-specific
nitrosamines as compared to cured unprocessed tobacco leaf of a
same type.
29. The tobacco leaf of claim 28, wherein the tobacco leaf is
flue-cured tobacco.
30. The tobacco leaf of claim 28, wherein the tobacco leaf is an
air-cured tobacco.
31. The tobacco leaf of claim 30, wherein the wash solution further
comprises a surfactant.
32. The tobacco leaf of claim 30, wherein the solvent is water or a
polar organic solvent.
33. The tobacco leaf of claim 30, wherein the disinfectant
comprises one or more of a chlorine-containing compound, peroxide,
a low molecular weight alcohol or a derivative thereof.
34. The tobacco leaf of claim 33, wherein the chlorine-containing
compound comprises one or more of chlorine dioxide, sodium
hypochlorite or sodium chlorite.
35. The tobacco leaf of claim 33, wherein the low molecular weight
alcohol comprises one or more methanol, ethanol or propanol.
36. A method of reducing tobacco-specific nitrosamines and
bacterial endotoxins from a harvested tobacco leaf before or during
curing comprising: washing the surface of the tobacco leaf with an
effective amount of a wash solution to reduce tobacco-specific
nitrosamines and bacterial endotoxins.
37. The method of claim 36, wherein the washing occurs at least
twice before completion of curing.
38. The method of claim 36, wherein the tobacco leaf is a green
leaf or a partially cured leaf.
39. The method of claim 36, wherein the curing comprises
flue-curing wherein the leaves are heated using a heat
exchanger.
40. The method of claim 36, wherein the wash solution comprises a
disinfectant dissolved or dispersed in a solvent.
41. The method of claim 40, wherein the wash solution further
comprises a surfactant.
42. The method of claim 40, wherein the solvent is water or a polar
organic solvent.
43. The method of claim 40, wherein the disinfectant comprises one
or more of a chlorine-containing compound, peroxide, a low
molecular weight alcohol, a quaternary ammonium compound, or a
derivative thereof.
44. The method of claim 43, wherein the chlorine containing
compound comprises one or more of chlorine dioxide, sodium
hypochlorite or sodium chlorite.
45. The method of claim 43, wherein the low molecular weight
alcohol comprises one or more of methanol, ethanol or propanol.
46. The method of claim 36, further comprising rinsing the washed
tobacco leaf with water.
47. The method of claim 36, wherein the wash solution is at a
temperature of from about 0.degree. C. to 55.degree. C.
48. The method of claim 47, wherein the wash solution is at a
temperature of from about 25.degree. C. to 55.degree. C.
49. The method of claim 36, wherein the wash solution consists
essentially of water heated to a temperature from about 25.degree.
C. to 55.degree. C.
50. The method of claim 49, wherein the wash solution consists
essentially of water heated to a temperature from about 25.degree.
C. to 55.degree. C.
51. The method of claim 36, wherein washing the surface of the
tobacco leaf further comprises agitating the tobacco leaf in one or
more directions.
52. The method of claim 36, wherein washing the surface of the
tobacco leaf comprises one or more of spraying, rinsing or
submerging the harvested tobacco leaf in the wash solution.
53. The method of claim 52, wherein washing the surface of the
tobacco leaf comprises submerging the tobacco leaf in the wash
solution for at least about 10 minutes.
54. The method of claim 52, wherein washing the surface of the
tobacco leaf comprises rinsing or spraying the surface of the
tobacco leaf with the wash solution such that the wash solution
runs freely from the surface of the tobacco leaf.
Description
[0001] The invention relates generally to tobacco curing and more
particularly to a method of treating and curing tobacco leaves so
as to have low levels of or no detectable tobacco-specific
nitrosamines and a reduced level of bacterial endotoxins as
compared to untreated, cured tobacco leaves.
BACKGROUND OF THE INVENTION
[0002] U.S. Pat. No. 5,040,550 to Argyropoulos and U.S. Pat. No.
4,448,208 to Friedrich et al. disclose processes of washing cured
tobacco leaves or leaf pieces with both hot and cold water for
extraction of resins, tar and nicotine as well as removal of
pesticide residue.
[0003] It has been reported that air-cured and flue-cured tobacco
contain tobacco-specific nitrosamines (TSNAs). See, "Effect of
Air-Curing on the Chemical Composition of Tobacco", Anna Wiernik et
al., Recent Adv. Tob. Sci, (1995), 21, pp. 39-80. According to
Wiernik et al., TSNAs are not present in significant quantities in
growing tobacco plants or fresh cut tobacco (green tobacco), but
are formed during the curing process. Bacterial populations which
reside on the tobacco leaves are stated to largely cause the
formation of nitrites from nitrate during curing and possibly
effect the direct catalysis of the nitrosation of secondary amines
at physiological pH values. The affected secondary amines include
tobacco alkaloids, which form TSNAs when nitrosated.
[0004] Star Tobacco and Pharmaceutical Co., Inc., has reported that
it treats tobacco leaves before or during flue-curing by
microwaving for purposes of reducing tobacco-specific nitrosamines.
See WO 98/58555. The microwaving adds significant cost to the
tobacco farmer, including the costs of excess handling and breakage
of tobacco leaves, the microwave process, the microwave facility
and the extra labor and time necessitated by the microwaving
process. A further drawback to this method of reducing TSNAs is
that microwaving of the tobacco leaves has a thermal effect upon
the tobacco tissue resulting in heating of the tobacco leaves which
may affect the taste and aroma of the smoke from the tobacco.
[0005] Because curing of tobacco leaves is normally performed by
the farmer who grows the tobacco, a simple, economical and
non-labor-intensive method of reducing the bacterial population
and/or activity, TSNA levels and bacterial endotoxin levels of the
cured tobacco leaves is desirable.
SUMMARY OF THE INVENTION
[0006] The present invention provides a method of treating tobacco
prior to or during curing with an aqueous solution of bicarbonate
or carbonate anions which is found to accelerate coloring of the
tobacco during cure and thereby shorten curing time, particularly
with Burley and other air cured tobaccos. When such treatment is
coupled with the step of an immediate drying of the tobacco at
conclusion of the curing process, the process achieves pronounced
reductions in tobacco-specific nitrosamines and bacterial
endotoxins in the cured tobacco leaves as compared to untreated
cured leaves.
[0007] Accordingly, the present invention provides a method of
treating air-cured tobacco with a wash solution of bicarbonate salt
or carbonate salt, wherein the air-cured tobacco is cured in four
weeks or less from the time of treatment with the wash solution,
and has one or more of a reduced or eliminated amount of
tobacco-specific nitrosamines, bacteria, bacterial activity and
bacterial endotoxins. At the election of the practitioner, such
air-cured tobacco may be selectively stripped from the stalk as the
leaves turn brown during curing, and dried.
[0008] In another embodiment, leaf of Burley tobaccos or other
variety of air-cured tobacco is primed at harvest, and the
individual leaves are treated as described above, cured and dried
so as to form cured leaves having a reduced or eliminated amount of
tobacco-specific nitrosamines and bacterial endotoxins.
[0009] In another preferred embodiment, a tobacco leaf is treated
with a wash solution of an antibacterial agent before or during
curing, wherein upon completion of the curing process the treated
tobacco leaf has a reduced or eliminated amount of tobacco-specific
nitrosamines and bacterial endotoxins.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a general representation of typical moisture,
temperature and TSNA content in tobacco during a traditional
flue-curing process of the prior art heating with a direct flame
and heating with use of a heat exchanger;
[0011] FIG. 2 is a general representation of bacterial population
during flue-curing; and
[0012] FIG. 3 is a general representation of moisture content
during traditional air-curing.
DETAILED DESCRIPTION OF THE INVENTION
[0013] It is believed that TSNAs are generated by chemical
breakdown of the tobacco leaf during the curing process or by the
action of bacteria during the curing process. The present invention
provides a process for reducing tobacco-specific nitrosamines, or
TSNAs, generated during the curing of tobacco leaves.
[0014] Tobacco leaf or leaves, as used herein, is meant to include
flue-cured and air-cured tobacco leaves which are green or
partially cured. Thus, tobacco leaf or leaves may indicate the
individual primed leaves of flue-cured tobacco (bright or Virginia
tobacco), or the stalk-cut leaves as attached to the stalk of the
tobacco plant or as individual leaves which have been primed. Cured
tobacco indicates tobacco leaves which have completed the curing
process.
[0015] Curing comprises the drying process for newly harvested
tobacco. Air curing is performed in widely ventilated barns under
natural atmospheric conditions (from which the name comes) with
little or no artificial heat; it takes 3-12 weeks, usually 6 to 8
weeks. Light air-cured tobacco is very thin to medium in body,
light tan shaded toward red to reddish brown in color, and mild in
flavor. Burley is light air-cured. Dark air-cured is medium to
heavy in body, light to medium brown in color. Flue curing is
performed in small, tightly constructed barns with artificial heat
beginning at 90.degree. F. and ending around 170.degree. F.; it
takes 5-7 days. The name comes from the metal flues used in the
heating apparatus. Flue-cured tobacco is yellow to reddish-orange
in color, thin to medium in body, and mild in flavor. Fire curing
is performed in ventilated barns with open fires (from which the
name comes) allowing the smoke to come in contact with the tobacco;
it is alternated with air curing. Fire-cured tobacco is light to
dark brown in color, medium to heavy in body, and strong in flavor.
Sun curing is performed on racks in the sunshine (from which the
name comes) for set daily periods over 4 weeks, depending on the
weather. Sun-cured tobacco looks similar to air-cured.
[0016] Harvesting tobacco is meant to include both priming and
stalk-cutting of tobacco.
[0017] Priming is meant to include removal of a tobacco leaf from a
growing or harvested tobacco plant.
[0018] Bacterial endotoxin, as used herein, is meant to include
both bacterial endotoxins generated by bacterial activity, and
materials which create a false positive for bacterial endotoxins in
the Limulus Amoebocyte Lysate (LAL) assay, such as .beta.-glucans
generated by fungal activity.
[0019] Bacterial populations on tobacco leaves are known to grow
linearly or exponentially (after a "lag") during curing in
accordance with prior, traditional curing practice. Bacteria gain
entrance into the tobacco leaf in large numbers through stomata or
cracks formed in the leaf cuticle by tissue necrosis, particularly
during lamina and stem drying of the tobacco. The bacterial
population of tobacco leaves, when harvested is about 10.sup.5 to
10.sup.6 bacteria/gram of dry weight of tobacco leaf. The heat of
the yellowing process during flue-curing and the prolonged exposure
time of air-curing both result in growth of the bacterial
population during yellowing. Bacterial populations may increase by
10 to 20 fold during this period. Many of these bacteria are
capable of reducing nitrates to nitrites. The nitrites may
accumulate in both the bacteria and the tobacco leaf cells. At
least some of the same bacteria are also capable of catalyzing the
nitrosation from nitrite of secondary amines.
[0020] Bacteria on tobacco leaves may result in the presence of
bacterial endotoxins. The bacterial populations found on tobacco
leaves are primarily gram negative bacteria, including pseudomonads
and enterobacters. These bacteria form lipopolysaccharides, or
bacterial endotoxins, which can remain as a residue even after the
bacteria have been destroyed.
[0021] Fungi may be present on tobacco plants when harvested.
Various fungi produce .beta.-glucans, which can result in a false
positive test for bacterial endotoxins, as quantified by the
Limulus Amoebocyte Lysate (LAL) assay.
[0022] The inventors herein have devised novel and cost effective
methods of reducing both the numbers and activity of bacterial and
fungal populations and, therefore, TSNAs and bacterial endotoxins
formed during the curing process. A preferred embodiment of the
invention comprises treating tobacco leaves prior to or during flue
curing or air curing by lavage with a wash solution having a
temperature from about 1.degree. C. to about 55.degree. C.
Antibacterial Lavage
[0023] In accordance with a preferred embodiment of the invention,
an antibacterial wash solution can be applied to green (e.g.,
growing or harvested tobacco plants or leaves) or partially cured
tobacco and preferably is capable of killing or disrupting the
biological activity of the bacteria and/or fungi present on tobacco
leaves. It is desirable that the solution have minimal chemical
reactivity with the tobacco leaf itself. It is an added advantage
if the solution also is able to saponify fats, has a detergent
effect, and/or is capable of raising the internal pH level of the
tobacco leaves. Raising the pH of the tobacco leaf aids in reducing
or eliminating nitrite levels by removing protons otherwise
available for use in nitrosation reactions. It is most preferable
that the solution have a bactericidal and/or bacteriostatic
activity, and desirable that it be capable of acting as a
surfactant.
[0024] The wash solution may include solutions of suitable
disinfectants such as, but not limited to solutions of
chlorine-containing compounds, such as chlorine dioxide, sodium
hypochlorite and sodium chlorite; peroxides; low molecular weight
alcohols, such as methanol, ethanol and propanol; quaternary
ammonium compounds such as benzalkonium chloride, octyl decyl
dimethyl ammonium chloride, decyl dimethyl ammonium chloride,
dioctyl dimethyl ammonium chloride and alkyl dimethyl benzyl
ammonium chloride; and derivatives thereof. Other disinfectant
solutions suitable for use will be apparent to practitioners in the
art. The disinfectant solution may be used in any effective
amount.
[0025] The disinfectant may be dissolved or dispersed in any
suitable aqueous or non-aqueous solvent, including but not limited
to water and polar organic solvents such as low molecular weight
alcohols, including methanol, ethanol and propanol. Other suitable
solvents will be apparent to practitioners in the art.
[0026] Particularly preferred solutions include disinfectant
solutions of chlorine-containing compounds, preferably chlorine
dioxide, dissolved in water. When the disinfectant is a low
molecular weight alcohol, a preferred solution is 70% ethanol in
water.
[0027] The disinfectant solution used to treat air-cured or
flue-cured tobacco is most preferably a saturated solution, though
any effective amount of disinfectant can be used. The solution may
be used at any desired temperature, for example, ambient
temperature. Depending on the particular disinfectant chosen, the
temperature of the solution may be raised or lowered to increase
solubility of the disinfectant. However, for ease of preparation
and use, it is most desirable to use a disinfectant having good
solubility at ambient temperature.
[0028] It may be desirable to add a surfactant to the wash solution
in order for the wash solution to better adhere to the tobacco leaf
surface. In particular, the addition of a surfactant is desirable
when the disinfectant is a chlorine-containing compound.
Surfactants used with chlorine-containing disinfectant compounds
are preferably bleach stable surfactants. Suitable surfactants will
be apparent to practitioners in the art, and may include, for
example, Dowfax.RTM. and Dowfax 2A1.RTM., but are not limited
thereto.
[0029] Tobacco leaves may be treated with a heated wash solution.
For instance, the solution can be heated to a suitable temperature
ranging from ambient up to about 55.degree. C. The solution may be
water or a disinfectant solution as described herein. While not
wishing to be bound by theory, it is believed that the heated
solution of water or disinfectant interrupts the biological
activity of the bacteria and/or fungi. Preferably, the solution is
hot enough to kill or arrest the activity of the bacteria or fungi
on contact or over the time during which the bacteria and/or fungi
are exposed to the solution by lavage while causing minimal or,
preferably, no damage to the tobacco leaf.
[0030] Gram-negative bacteria, as well as other bacteria on tobacco
leaves, are temperature sensitive. They thrive in increased heat,
multiplying in numbers, but die when exposed to temperatures of
about 50.degree. C. or greater for an extended period of time.
Therefore, the wash solution may be heated to a temperature of from
about 25.degree. C. to about 55.degree. C. in order to kill or
disrupt the biological activity of the bacteria. The length of
lavage needed at any particular temperature to effectively reduce
bacterial and fungal populations or their activity will be apparent
to practitioners in the art based on factors such as the type and
amount of bacteria and/or fungal growth present, the integrity of
the tobacco leaves, and the like.
[0031] The solution, whether disinfectant, heated disinfectant or
heated water, is applied to the tobacco leaves by any means
possible, particularly by rinsing or spraying or dipping the leaves
in the solution. Whether the tobacco leaves are sprayed or dipped,
agitation of the tobacco leaves is helpful to evenly distribute the
solution, and to aid in removing the bacterial and fungal
populations by effectively shaking the bacteria and fungal growth
off the tobacco leaves. Agitation of the leaves in multiple
directions is preferable, for example, front to back, side to side
and up and down. If the leaves are lavaged (washed) by spraying, it
is preferred that the leaves be entirely soaked so that the
solution is running freely from all leaf surfaces. Preferably, the
tobacco leaves are dipped in the solution and agitated for a period
of time. More preferably, the leaves are completely submerged for a
period of at least 10 minutes, most preferably at least 15 to 20
minutes, with gentle agitation of the tobacco leaves throughout the
entire period of submersion.
[0032] During lavage, some or all of the bacteria and fungi on the
leaf surfaces are washed off the leaf surface. The bacteria may
also be killed or harmed in the wash solution by other chemical or
mechanical interactions effected by the lavage.
[0033] The tobacco leaves are preferably ravaged one or more times
before completion of lamina drying or onset of necrosis in the
leaves. In particular, lavage may be performed on green leaves,
during yellowing, at the conclusion of yellowing, and, potentially,
early during lamina drying. Lavage may be performed after yellowing
and during lamina drying so long as the leaf cuticle is still
substantially intact. It is desirable that the tobacco leaves not
be washed after the cuticle of the tobacco leaves has been damaged
to a significant extent, because this might allow the solution to
penetrate into the interior of the tobacco leaf. Therefore, lavage
of tobacco leaves may occur at any point, preferably before the
leaf cuticle is substantially compromised.
[0034] It is preferable to lavage the tobacco leaves before or
during yellowing to remove bacterial populations before they can
significantly increase in number and before they can do a
significant amount of damage to the tobacco leaves. In particular,
it is most preferable to lavage green tobacco leaves, i.e., leaves
which have not yet begun the curing process. Leaves undergoing
yellowing may also be lavaged with good results. However, lavaging
flue-cured tobacco leaves at the end of yellowing or during or
after lamina drying of the flue-cured tobacco leaves is of lesser
use because the heat of lamina drying and removal of water in
flue-curing will eventually kill or arrest the activity of most
bacteria dependent upon the degree to which desiccation of the leaf
is achieved.
[0035] Lavage of the tobacco leaves may occur more than once during
the curing process. However, excessive lavage of the leaves is not
necessary. Preferably, green tobacco leaves are lavaged by spraying
or washing thoroughly with a wash solution with or without
agitation. For instance, the growing tobacco plants can be sprayed
in the field close to harvest time or harvested plants or green
tobacco leaves can be submerged with agitation in a wash solution.
The tobacco leaves can be additionally rinsed or sprayed or
submerged at least once, with or without agitation, during
yellowing or after yellowing. Practitioners in the art will
recognize that the lavage treatment can be adjusted to take into
account numerous factors, such as the type of leaf and, therefore,
the curing process being used (flue-cured or air-cured), the
temperature and humidity conditions during curing, the length of
time the leaves require to complete each step of curing, the
appearance of the leaves themselves and the amount of bacteria or
fungal growth present, etc.
[0036] After lavage with a disinfectant wash solution such as by
spraying or immersion, the treated leaves may optionally be rinsed
with plain water in order to remove the disinfectant solution.
Because flue-curing requires rapid drying and high heat,
particularly during lamina and stem drying, additional bacterial
growth is minimal and the disinfectant solution is not necessary to
control the bacterial population in these stages of curing. Some
residual solution may be left on the leaves during flue-curing as
well as air-curing, if desired. With the slow drying process of
air-cured tobacco, the residuals can discourage bacterial growth
and interfere with nitrosation reactions.
[0037] In the case where lavage is performed during curing, curing
of the tobacco leaves can be resumed immediately or within 24 hours
or less. The excess fluid on the leaves from lavage may be allowed
to drip off the leaves and dry naturally, or forced air or heat may
be used to hasten drying. Also, the leaves can be optionally rinsed
with water. Forced air may be supplied by any means, such as by a
fan or blower, or the curing barn may be opened for maximum
ventilation. Other methods of forcing increased ventilation of the
barn to hasten drying of the tobacco leaves, or of heating the
leaves, will be apparent to practitioners in the art.
Flue-Cured Tobacco
[0038] Plants used for flue-cured tobacco (bright or Virginia
tobacco) are grown, topped, ripened, harvested and then cured.
Harvesting is undertaken by removing (priming) several leaves at
intervals as the leaves ripen. The leaves are generally considered
ripe when the midvein turns white. The leaves are removed beginning
from the bottom of the stalk, and higher leaves are primed as they
ripen. Primed leaves are bundled and placed in barns for curing.
With traditional flue curing practices, the farmer initially
maintains the barn at a high humidity, approximately 89% relative
humidity, and at a temperature of about 30 to 35.degree. C. (85 to
95.degree. F.) for several days to effect yellowing of the leaf.
After yellowing, the color of the leaves is fixed by heating the
leaves to effect drying of the leaf lamina. Drying of the lamina is
accomplished by raising the temperature in the barn to about 49 to
60.degree. C. (120 to 140.degree. F.) for 24 to 36 hours. Heating
of the barn may be effected by any means, but generally propane
heat is used. Once lamina drying has occurred, the farmer heats the
barn to about 72 to 77.degree. C. (160 to 170.degree. F.) for 1 to
3 days to dry the mid-vein or stem of the leaves.
[0039] During the above drying processes, the leaves first take on
a yellow color and chemical decomposition of the leaves begins,
breaking down starch in the leaves to sugar, proteins to amino
acids, and the like. As the tobacco leaves dry and turn brown, they
become brittle and undergo necrosis, whereby the cuticle of the
leaf cracks, exposing interior portions of the leaf tissues. After
lamina and stem drying, the tobacco leaves are bulked or bundled
together, and the moisture level within the leaves is raised
("reordered") to approximately 10 to 15% to facilitate handling of
the tobacco leaves with less breakage. The tobacco leaves are then
graded and sold to tobacco product manufacturers. See Colin L.
Browne, The Design of Cigarettes, (1990) Hoechst Celanese
Corporation, pp. 13-19. Flue-cured tobacco has a low nitrogen and
high sugar content.
[0040] Flue-cured tobacco, such as bright tobaccos (or Virginia),
that have undergone curing in barns directly heated with propane
heat exhibit higher levels of TSNAs than does tobacco in similar
barns equipped with heat exchangers. See D. M. Peele et al.,
"Formation of Tobacco Specific Nitro-samines in Flue-Cured
Tobacco," 53.sup.rd Tobacco Science Research Conference (1999) Vol.
53, pp. 68-69. Without wishing to be bound by theory, it is
believed that allowing combustion gases containing oxides of
nitrogen from the burning propane to impinge directly upon the
curing leaves provides the primary source of TSNA formation in
flue-cured-tobacco. Bacterial contributions to TSNA formation in
flue-cured tobacco may be relatively minor. However, TSNA levels in
flue-cured tobacco are also affected by the integrity of the green
leaf before curing. Leaf damage and infection of tissue (so-called
"barn rot") in the green leaf may cause increased TSNA levels from
bacterial invasion of the damaged tobacco leaf.
[0041] The lavage treatment in accordance with the invention is
beneficial in that TSNAs and endotoxins in the tobacco leaves can
be reduced prior to the onset of conditions during flue curing
favorable to bacterial growth and/or TSNA production.
[0042] FIG. 1 is a graphical representation showing the typical
effects of flue curing on tobacco leaf moisture content in terms of
oven volatiles (curve A), TSNA content (curve B) including effects
of heating using direct fire propane (curve C) or using heat
exchangers (curve D), and temperature (curve E). As shown by curves
C and D, the effect of direct fire heating with propane raises the
TSNA content considerably compared to heating with heat exchangers.
In FIG. 1, various stages of curing are identified with: G (green),
Y (yellowing), L (lamina drying) and MV (midvein drying). At the
conclusion of flue curing, the leaves preferably have a moisture
content of about 10% (oven volatiles). Afterwards, the leaves are
preferably reconditioned to a moisture content of about 10 to
16%.
[0043] FIG. 2 shows the effects of the lavage treatment with a
bactericidal agent in accordance with the invention on reducing the
bacterial population on flue-cured bright tobacco. Curve A
corresponds to flue cured tobacco which has not been subjected to a
lavage treatment in accordance with the invention whereas curve B
corresponds to flue cured tobacco which has been subjected to a
lavage treatment. With antibacterial lavage, the inoculum (initial
bacterial population) is lower. As a result, there is a greater lag
period (the period after inoculation before which exponential
growth of the bacteria population begins).
EXAMPLE I
Antibacterial Lavage
[0044] Bright tobacco from the 5th leaf position (tip) was
harvested and loaded into standard Bulktobac curing racks
(approximately 70 lbs. per rack). Individual racks were immersed in
70% ethanol for either 1 or 5 minutes then rinsed in water. After
draining thoroughly the treated tobacco along with untreated
control material was cured in a Bulktobac 32-rack curing barn
equipped with a heat exchanger. A standard flue-curing profile was
followed and the resultant tobaccos were lyophilized, ground and
assayed for microbial counts. The results indicated that the
ethanol treatment reduced the bacterial load in a dose dependent
manner 1 to 2 orders of magnitude as compared to the control for
the 1 and 5 minutes treatments, respectively. That is, the control
exhibited a 10.sup.8 count whereas the 1 minute treatment exhibited
a 10.sup.7 count and the 5 minute treatment exhibited a 10.sup.6
count. Similar results were achieved for treatment of the tobacco
with 10.7 ppm ClO.sub.2 in aqueous solution also using a 1 or 5
minute soak time and handling identically to the ethanol treated
material.
Alkaline Lavage
[0045] In a typical air-curing process, tobacco plants are cured in
an enclosure such as a barn for six to seven weeks. It has been
found that bacteria and/or TSNAs begin to increase significantly
after about 21/2 weeks under such conditions.
[0046] The alkaline lavage treatment in accordance with the
invention surprisingly and unexpectedly can reduce the curing time
such that air-curing is completed before the onset of the
conditions ripe for substantial bacteria growth and/or TSNA
production. Due to more accumulation of TSNAs in the midveins of
the leaves than in the lamina during air-curing, the midveins can
optionally be removed from the cured leaves prior to further
processing thereof.
[0047] Air-cured tobacco, which has traditionally comprised burley
or Maryland tobaccos, is grown, topped, ripened and then harvested
by cutting the entire plant at the base, known as stalk-cutting.
Under prior, traditional practices, the plant is harvested when
leaves approximately midway up the stalk have ripened. Usually, the
stalk-cut tobacco is left to wilt for several days and then cured
by being hung upside down along racks in a barn at a relative
humidity of approximately 65 to 70% for 6 to 10 weeks. Heat and
humidity levels are controlled by simply opening and closing
ventilation ports in the barn. Generally, the yellowing process
takes about 10 to 12 days, the leaves on the stalk turn from yellow
to brown in another 6 to 7 days, and lamina and stem drying occur
over an additional 30 to 40 days. The length of time for
air-curing, and in particular for each individual step of
air-curing, is highly dependent on the ambient temperature and
relative humidity in the barn during air-curing. Air-cured tobacco
generally has a very low sugar content and a high nitrogen content.
In air curing external sources of nitrogen oxides are not present
suggesting that bacterial action is the major cause of nitrosation
in air-cured tobacco.
[0048] FIG. 3 is a general representation of the effects of
air-curing on tobacco leaf moisture, wherein curve A represents the
moisture content of the tobacco leaf midvein and curve B represents
the moisture content of the tobacco leaf lamina.
[0049] In accordance with a preferred embodiment of the present
invention, i.e., the "alkaline lavage", the use of a solution of
bicarbonate salt, preferably sodium bicarbonate, or carbonate salt,
preferably sodium carbonate (Na.sub.2CO.sub.3), to treat air-cured
tobacco such as burley has surprisingly and unexpectedly been found
to decrease the air-curing time of the tobacco by at least about
25%, and preferably by about 50% or more. It has unexpectedly been
discovered that green leaves of air-cured tobacco lavaged with a
wash solution of bicarbonate salt before or immediately after
commencing curing can turn brown within two weeks of the "alkaline
lavage", as opposed to the normal four to six week period required
from the start of curing. The treated leaves are moist and pliable
when brown in contrast to the dry and brittle brown leaves of
conventional air-curing. Using the lavage treatment in accordance
with the invention, it has been found that leaves higher on the
stalk have mostly brown lamina but somewhat yellow midveins after
about two weeks of air curing.
[0050] In order to accommodate the different cure rates of the
treated leaves, brown leaves can be selectively stripped from the
hung stalk and dried by further air-curing at low humidity (below
about 65%) and temperature or by circulating dry air or by heating,
similar to what is used in flue-curing. The drying after priming
preferably commences within 24 hours of stripping the leaf, and is
preferably completed within 3 days or less. Such drying may in the
alternative, be applied to the cured tobacco as it remains hanging
in the barn. Preferably, the drying step reduces the moisture
content to at or below approximately 30 to 10% (oven volatiles),
more preferably near 10% oven volatiles. The stripped leaf may be
destemmed prior to drying, if desired, so as to remove from the
usable tobacco lamina the midrib and any nitrosamines that may
reside in the midrib.
[0051] The advantages of treating air-cured tobacco with a
bicarbonate or carbonate salt solution are a shorter curing period
of about 4 weeks or less, preferably 3 weeks or less, allowing
additional harvests to be planted and air-cured in a season;
lowered or eliminated bacterial levels or activity; lowered or
eliminated TSNA levels; and lowered or eliminated bacterial
endotoxin levels. The shortened curing time of the treated
air-cured tobacco further aids in retarding bacterial growth, and
therefore in reducing TSNA and bacterial endotoxin levels in the
cured tobacco.
[0052] Although bicarbonate and carbonate solutions are preferred
as curing-accelerating agents, it is believed that any suitable
alkaline solution could be applied to the tobacco plant to shorten
the time for the harvested tobacco to brown, or turn dark. The
preferred wash solutions comprise aqueous solutions of carbonate
and/or bicarbonate salts, particularly sodium carbonate and sodium
bicarbonate, and/or other such salts such as potassium carbonate,
potassium bicarbonate and ammonium carbonate. Other solutions (for
example, dilute aqueous solutions of sodium hydroxide and/or
potassium hydroxide) will be readily apparent to practitioners in
the art after reading and understanding this disclosure.
[0053] Alternatively, air-cured tobacco leaves may be primed from
the tobacco plant as they ripen (i.e., lower leaves are removed
first), optionally destemmed, and cured with treatment as described
herein to reduce or eliminate nitrosamine levels, bacteria,
bacterial activity and/or bacterial endotoxins. Preferably, the
leaves are treated with a carbonate and/or bicarbonate salt
solution for accelerated curing as described herein.
EXAMPLE II
Alkaline Lavage
[0054] The "Carbonate Lavage"--Freshly stalk-cut harvested burley
(Tn90) plants were hung on a stick, 5 plants per stick and hung on
a scaffold, whereupon, leaves were sprayed until run-off with an
aqueous solution of either 1% or 2% (weight/volume) of NaHCO.sub.3
(sodium bicarbonate) and allowed to dry and wilt for three days and
then hung in a conventional air-curing barn. Untreated controls
were included. Once cured, the tobacco was dried (fixed) by passing
dry air about the cured tobacco, preferably at approximately
85.degree. F. By two weeks, older leaves (at the lower stalk
positions) had become so brown as to be undistinguishable in
pigmentation from untreated leaves that had cured for at least four
to six weeks. The browned bicarbonate-treated leaves remained moist
and pliable, in contrast to the dry and friable lamina that had
been equivalently browned by conventional curing. Leaves at higher
stalk positions of treated plants, i.e., developmentally younger
leaves, had undergone complete browning at the tips and significant
browning of their lamina after two weeks of curing, but their
midveins were still somewhat yellow.
[0055] The following data was obtained upon chemical analyses of
the tobacco described in this Example:
1 TN90 NaHCO.sub.3 Treated At 5 Weeks of Curing Description LL PM
LL PM LL PM LL PM Bacteria (% NNN NAT NAB NNK per Total
NaHCO.sub.3) (ng/g) (ng/g) (ng/g) (ng/g) gram TSNA's Control 0%
2071 3841 61 174 1.80E+06 6147 1% 639 1250 30 51 1.31E+03 1970 2%
329 1070 24 40 1.31E+05 1463
[0056] In addition to the reduction in the amount of time necessary
for color development, the bicarbonate treated material displayed a
reduction of total TSNA content (in ng/g) of 68% and bacterial load
(in bacteria/g) of 3 orders of magnitude.
[0057] While the invention has been described with reference to
preferred embodiments, it is to be understood that variations and
modifications may be resorted to as will be apparent to those
skilled in the art. Such variations and modifications are to be
considered within the purview and scope of the invention as defined
by the claims appended hereto.
* * * * *