U.S. patent application number 14/702347 was filed with the patent office on 2016-01-14 for methods to treat mixtures of glycosides to obtain one or more of these glycosides in more pure form.
The applicant listed for this patent is CARGILL, INCORPORATED. Invention is credited to Aron Broman ERICKSON, John Joseph HAHN, Allan Stuart MYERSON, Andrew Keith OHMES, Troy Allen RHONEMUS, Kern M. STORO, Christopher Austin TYLER.
Application Number | 20160009749 14/702347 |
Document ID | / |
Family ID | 44319766 |
Filed Date | 2016-01-14 |
United States Patent
Application |
20160009749 |
Kind Code |
A1 |
ERICKSON; Aron Broman ; et
al. |
January 14, 2016 |
METHODS TO TREAT MIXTURES OF GLYCOSIDES TO OBTAIN ONE OR MORE OF
THESE GLYCOSIDES IN MORE PURE FORM
Abstract
The present invention provides methods to treat mixtures
containing natural rebaudioside A (Reb A), rebaudioside B (Reb B),
and rebaudioside D (Reb D), synthetic counterparts of these, and/or
derivatives of the natural or synthetic embodiments obtain one or
more of these glycosides in more pure form. In many embodiments,
the invention can be used to process glycoside mixtures obtained at
least in part from natural sources such as the Stevia plant. This
allows, for instance, the recovery of a product including Reb A
material in more pure form relative to Reb B material or Reb D
material. As an alternative or in addition to recovery of the
purified Reb A material, a product including Reb B material and/or
Reb D material in more pure form relative to Reb A material can be
obtained.
Inventors: |
ERICKSON; Aron Broman;
(Boulder, CO) ; HAHN; John Joseph; (Woluwe-St
Pierre, BE) ; MYERSON; Allan Stuart; (Chicago,
IL) ; OHMES; Andrew Keith; (Jordan, MN) ;
RHONEMUS; Troy Allen; (Plymouth, MN) ; STORO; Kern
M.; (Burnsville, MN) ; TYLER; Christopher Austin;
(Minnetonka, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CARGILL, INCORPORATED |
WAYZATA |
MN |
US |
|
|
Family ID: |
44319766 |
Appl. No.: |
14/702347 |
Filed: |
May 1, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13575751 |
Jul 27, 2012 |
9024012 |
|
|
PCT/US11/22741 |
Jan 27, 2011 |
|
|
|
14702347 |
|
|
|
|
61299160 |
Jan 28, 2010 |
|
|
|
Current U.S.
Class: |
536/18.1 |
Current CPC
Class: |
A23V 2002/00 20130101;
A23L 2/60 20130101; C07H 15/256 20130101; A23L 27/36 20160801 |
International
Class: |
C07H 15/256 20060101
C07H015/256; A23L 1/236 20060101 A23L001/236 |
Claims
1-62. (canceled)
63. A method of treating a glycoside mixture comprising
rebaudioside A material and at least one of rebaudioside B material
or rebaudioside D material to help recover at least one of
rebaudioside A material, rebaudioside B material or rebaudioside D
material in more pure form, comprising the steps of: a) providing a
slurry comprising glycosides including at least rebaudioside A
material and at least one of rebaudioside B material and
rebaudioside D material, wherein the slurry includes a solid phase
and a liquid phase; b) aging the slurry at one or more elevated
temperatures independently greater than about 40.degree. C., said
aging occulting for a time period sufficient for the solid phase to
become more pure with respect to at least one of the rebaudioside A
material, rebaudioside B material and rebaudioside D material; c)
filtering the heated mixture to separate the solid and liquid
phases, wherein the mixture is at a temperature of at least
40.degree. C. during at least a portion of the filtering; and d)
recovering at least one glycoside in at least one of the solid and
liquid phases.
64. The method of claim 63, wherein step (d) comprises recovering a
solid phase comprising rebaudioside A material.
65. The method of claim 63, wherein step (d) comprises recovering a
liquid phase comprising at least one of rebaudioside B material and
rebaudioside D material.
66. The method of claim 65, further comprising the step of
processing the liquid phase to recover a solid phase containing at
least one of rebaudioside B material and rebaudioside D
material.
67. The method of claim 63, wherein the slurry provided in step (a)
includes from about 20 weight percent to about 96 weight percent of
rebaudioside A material.
68. The method of claim 63, wherein the slurry provided in step (a)
includes at least about 3 weight percent total of rebaudioside B
material and rebaudioside D material.
69. The method of claim 63, wherein the slurry provided in step (a)
includes at least about 6 weight percent total of rebaudioside B
material and rebaudioside D material.
70. The method of claim 63, wherein the slurry is treated in step
(b) under conditions such that the solid phase resulting from step
(c) includes at least 80 weight percent rebaudioside A
material.
71. The method of claim 63, wherein the slurry is treated in step
(b) under conditions such that the solid phase resulting from step
(c) includes at least 90 weight percent rebaudioside A
material.
72. The method of claim 63, wherein the slurry is treated in step
(b) under conditions such that the solid phase resulting from step
(c) includes at least 96 weight percent rebaudioside A
material.
73. The method of claim 63, wherein the slurry is treated in step
(b) under conditions such that the solid phase resulting from step
(c) comprises a crystalline phase that includes up to about 3
weight percent total rebaudioside B material and rebaudioside D
material.
74. The method of claim 63, wherein the liquid phase in at least
one of steps (a) through (d) comprises at least one alcohol.
75. The method of claim 74, wherein the alcohol is an aqueous
alcohol.
76. The method of claim 63, wherein the liquid phase in at least
one of steps (a) through (d) comprises an alcohol selected from
ethanol, isopropanol, methanol, n-butanol, and combinations
thereof.
77. The method of claim 76, wherein the alcohol is an aqueous
alcohol.
78. The method of claim 63, wherein the liquid phase in at least
one of steps (a) through (d) comprises water.
79. The method of claim 63, wherein the slurry provided in step (a)
comprises an alcohol crystalline form of at least one of
rebaudioside A material, rebaudioside B material, and rebaudioside
D material.
80. The method of claim 63, wherein aging occurs at a temperature
of at least about 50.degree. C.
81. The method of claim 63, wherein aging occurs at a temperature
of at least about 70.degree. C.
82. The method of claim 63, wherein aging occurs at a temperature
of at least about 70.degree. C. and a pressure greater than ambient
pressure.
83. The method of claim 63, wherein aging occurs at an absolute
pressure in the range from about 1.1 atm to about 30 atm.
84. The method of claim 63, wherein aging occurs at an absolute
pressure in the range from about 1.1 atm to about 10 atm.
85. The method of claim 63, wherein aging occurs at an absolute
pressure in the range from about 1.1 atm to about 5 atm.
86. The method of claim 63, wherein aging occurs with mixing in the
presence of a cooling surface that is at a temperature less than
the bulk temperature of the mixture.
87. The method of claim 86, wherein at least a portion of the
cooling surface is at a temperature of under about 40.degree. C.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. provisional
application Ser. No. 61/299,160 filed 28 Jan. 2010 entitled METHODS
FOR THE PURIFICATION OF REBAUDIOSIDE B AND REBAUDIOSIDE D FROM
REBAUDIOSIDE A COMPOSITIONS, which is hereby incorporated by
reference in its entirety.
FIELD OF THE INVENTION
[0002] The methods of the present invention relate to treatments
that resolve mixtures including rebaudioside A material,
rebaudioside B material, and rebaudioside D material into more pure
form(s). For example, mixtures of rebaudioside A, B, and D can be
resolved to provide the Reb A on the one hand, and/or the Reb B
and/or D on the other hand, in more pure form. More specifically,
the treatments use one or more crystallization strategies singly or
in combination to purify such glycoside mixtures.
BACKGROUND
[0003] The species Stevia rebaudiana ("Stevia") has been the
subject of considerable research and development efforts directed
at the purification of certain naturally occurring sweet glycosides
of Stevia that have potential as non-caloric sweeteners. Sweet
glycosides (also referred to as steviol glycosides) that may be
extracted from Stevia include the six rebaudiosides (i.e.,
rebaudioside A to F), stevioside (the predominant glycoside in
extracts from wild type Stevia), dulcosides, and sterebins.
[0004] Rebaudioside A (Reb A) is a sweet tasting glycoside
component of Stevia, having roughly 250-450 times the sweetness of
sucrose. Rebaudioside A is desirable for use in non-caloric
sweeteners because of its favorable sweetness profile, regulatory
approvals, customer acceptance, and minimal bitter aftertaste.
Rebaudioside B (Reb B) and D (Reb D) also are sweet tasting
glycoside components of Stevia that are of interest for their
sweetness characteristics.
[0005] The natural extracts of Stevia as well as some processed
versions thereof as well as synthetic counterparts typically
include mixtures of glycosides. It has been desirable to purify
these mixtures to obtain one or more of these glycosides in more
pure form. For instance, a mixture might include, among other
ingredients, a combination of Reb A, Reb, B, and Reb D. It has been
desirable in some instances to treat these mixtures to recover a
product that includes Reb A in more pure form while reducing the
content of Reb B and/or D in the product. In other instances, it
may be desirable to treat these mixtures to recover a product that
includes Reb B and/or Reb D in more pure form while reducing the
content of Reb A in the product. In still other instances, these
mixtures are processed to recover a combination of products. For
instance, if a mixture is treated to recover a mixture portion that
is more pure with respect to Reb A with reduced Reb B and Reb D,
another portion of the treated mixture generally can be recovered
that has more pure Reb B and/or D and less Reb A content
[0006] Numerous methods have been reported for the purification of
rebaudioside A from crude Stevia extracts containing rebaudioside
A.
[0007] Japanese Publication No. 56121454 reports a method of
separating stevioside and rebaudioside A at high purity and yield
by crystallization. In the method a mixture of stevioside and
rebaudioside A is extracted from the leaves and stalks of Stevia
rebaudiana Bertoni by conventional process. The extract is
dissolved in .gtoreq.70% aqueous solution of ethanol and
rebaudioside A is selectively crystallized from the solution.
[0008] Japanese Patent 63173531 describes a method of extracting
sweet glycosides from the Stevia rebaudiana plant. The first step
of the process is to extract a liquid solution of sweet glycosides
from the Stevia rebaudiana plant. Secondly, the liquid solution of
sweet glycosides is passed through a non-polar porous resin and is
eluted with a water-soluble organic solvent, preferably methanol.
Thirdly, the eluted solution is concentrated and dried to give a
powdery material. This procedure isolates a mixture of sweet
glycosides, but does not isolate a single pure sweet glycoside such
as rebaudioside A.
[0009] U.S. Patent Application Publication No. 2006/0083838
(Jackson et al.) reports a method of isolating and purifying
rebaudioside A from commercially available Stevia rebaudiana
starting material. The method comprises: (1) an ethanol (EtOH)
formulation stage to formulate a selected EtOH solvent, (2) a first
reflux stage using the Stevia starting material and optionally
additional reflux stages using retentate isolated from a refluxed
mixture or a stirred wash mixture, (3) optionally, one or more
stirred wash stages, and (4) an ethanol purge and drying stage. In
the reported method, an EtOH formulation stage is conducted in
order to formulate a desired reflux solvent for use in the reflux
step(s). Typically, the reflux solvent is a mixture of ethanol and
water with about 5% to 15% by volume water. The reflux stage
typically comprises providing a mixture of glycosides in the reflux
solvent and refluxing the mixture for about 1 hour, cooling the
mixture to improve the process yield, and filtering. The process
further includes one or more energy-intensive refluxing steps that
are typically conducted at a temperature of about 79.degree. C. to
80.degree. C. for about 1 hour. The stirred wash stage typically
comprises providing a mixture of glycosides from a reflux stage and
a solvent of pure ethanol, agitating the mixture at room
temperature for about 15 minutes, and filtering. The method
allegedly produces 100% pure, water-soluble rebaudioside A.
[0010] U.S. Pat. No. 5,962,678 (Payzant et al.) reports a method of
extracting selected sweet glycosides from the Stevia rebaudiana
plant. In the reported method, sweet glycosides are extracted from
the Stevia plant and are processed to obtain individual components
in a multi-step process. First, the Stevia plant is treated to
extract an aqueous liquid solution containing mixed sweet
glycosides. By using a series of ion exchange resins, the impure
non-sweet glycosides are separated from the mixed sweet glycosides,
which are dried. These dried mixed sweet glycosides, which still
contain impurities, are then dissolved in a water-soluble organic
solvent such as anhydrous methanol to form a solution. The solution
is refluxed and is cooled to precipitate a first sweet glycoside
component. This first sweet glycoside component, which is typically
stevioside, can be recovered by filtration and may be further
purified by the method described for the second component. The
filtrate from the crystallization of the first precipitated sweet
glycoside can be further treated to obtain a second sweet glycoside
component by concentrating the filtrate by heating. Upon cooling
the solution, a second sweet glycoside component precipitates which
can be recovered. This second sweet glycoside component is
typically rebaudioside A. It can be further purified by dissolving
it in a water-soluble organic solvent such as methanol that may
optionally contain a small amount of water. The solution is heated,
refluxed, and finally cooled to precipitate the second sweet
glycoside component at a higher purity. The precipitate can be
recovered by filtration. This purification process can be repeated
until a final crystallized solid of desired purity is obtained. The
method reports Rebaudioside A purity levels of 90% or greater or
95% or greater.
[0011] U.S. Pat. No. 4,361,697 (Dobberstein et al.) reports a
process for recovering diterpene glycosides from the Stevia
rebaudiana plant. The process includes the steps of sequentially
extracting plant material with a first solvent of intermediate
polarity to extract plant substances which tend to interfere with a
liquid chromatographic separation of the glycosides, and then with
a second solvent of high polarity to extract glycosides, and
chromatographically separating the extracted glycosides by
introducing them onto a liquid chromatography column having a
packing of an oxygen-containing organic stationary phase covalently
bonded through a silicon atom to an inorganic support. The
glycosides are eluted with a solvent of polarity that is higher
than that of the first solvent but lower than that of the second
solvent.
[0012] U.S. Pat. No. 4,892,938 (Giovanetto) reports a method for
recovering steviosides from dried plant material of Stevia
rebaudiana Bertoni by extraction and purification. An extract is
obtained through treatment in water at a temperature from room
temperature to about 65.degree. C. with stirring and subsequent
filtration and centrifugation. This extract is treated with calcium
hydroxide, whereupon a precipitate is obtained by means of
filtration or centrifugation. This precipitate is treated with a
strongly acidic ion exchange resin and subsequently with a weakly
basic ion exchange resin, filtered and dried.
[0013] U.S. Pat. No. 4,082,858 (DuBois) reports a method for the
recovery of rebaudioside A from the leaves of Stevia rebaudiana
plants. Final purification is achieved by liquid chromatography
subsequently followed by an initial extraction with water and
alkanol having from 1 to 3 carbon carbons, preferably methanol. It
is also disclosed that water may be used as the initial solvent.
Their preferred solvent at this stage is a liquid haloalkane having
from 1 to 4 carbon atoms. The preferred second solvent is an
alkanol having from 1 to 3 carbon atoms, while the preferred third
solvent is an alkanol having from 1 to 4 carbon atoms and
optionally minor amounts of water.
[0014] U.S. Patent Application No. 2006/0134292 (Abelyan et al.)
reports a process for recovering sweet glycosides from Stevia
rebaudiana plant material. The dried and powdered leaves are
treated with water in the presence of a pectinase, cellulase, and
alpha-amylase. The use of such enzymes is reported to considerably
increase the extraction rate and facilitates the next stages of
purification. The resulting extract is purified using treatment
with calcium hydroxide and ultrafiltration. The permeate is passed
through the column packed with bentonite and concentrated to syrup
state under vacuum. The treatment with ethanol allows separating
the practically pure rebaudioside A from the mixture. The
rebaudioside A with high purity is obtained after washing the
crystals with 88-95% of ethanol.
[0015] Other techniques include those reported, for example, in
Japanese Publication Nos. 56121454; 56121455; 52062300; and
56121453 assigned to Ajinomoto Company, Inc, and in Chinese
Publication No. 1243835 assigned to Hailin Stevia Rebaudium
Sugar.
[0016] Due to their values as non-caloric sweeteners, improvements
in the available methods for purifying glycosides such as Reb A,
Reb B, and/or Reb D are desired. In particular, a method that
allows for the separation of rebaudioside A from compositions
containing rebaudioside B and/or rebaudioside D is highly
desirable. This would allow recovery of a product that has more
pure Reb A, a product that has more pure Reb B and/or D, or both
kinds of products.
SUMMARY
[0017] The present invention provides methods to treat mixtures
containing natural rebaudiosides A, B, and D, synthetic
counterparts of these, and/or derivatives of the natural or
synthetic embodiments to obtain one or more of these glycosides in
more pure form. In many embodiments, the invention can be used to
process glycoside mixtures obtained at least in part from natural
sources such as the Stevia plant. This allows, for instance, the
recovery of a product including Reb A in more pure form relative to
Reb B or D. As an alternative or in addition to recovery of the
purified Reb A, a product including Reb B and/or D in more pure
form relative to Reb A can be obtained.
[0018] Principles of the present invention allow excellent
purification of these glycosides to be achieved at high yield.
Conventionally, high purity has been obtained at the expense of
yield and vice versa. Providing methodologies that offer high
levels of both yield and purification is a significant advantage,
particularly at industrial scales.
[0019] The treatments of the present invention can be used in
combination with other purification strategies. In such
combinations, the methods of the present invention can be practiced
before and/or after the other strategies are used. In some modes of
practice, such combinations can be repeated one or more additional
times.
[0020] In one aspect, the present invention relates to a method of
treating a glycoside mixture comprising Reb A material and at least
one of Reb B material or Reb D material to help recover at least
one of the Reb A material, Reb B material, or Reb D material in
more pure form, comprising the steps of: [0021] a) providing a
slurry comprising glycosides including at least rebaudioside A
material and at least one of Reb B material and D material, wherein
the slurry includes a solid phase and a liquid phase; [0022] b)
aging the slurry at one or more elevated temperatures independently
greater than about 40.degree. C., said aging occurring for a time
period sufficient for the solid phase to become more pure with
respect to at least one of the rebaudioside A material, B material
and D material; [0023] c) filtering the heated mixture to separate
the solid and liquid phases, wherein the mixture is at a
temperature of at least 40.degree. C. during at least a portion of
the filtering; and [0024] d) recovering at least one glycoside in
at least one of the solid and liquid phases.
[0025] In another aspect, the present invention relates to a method
of treating a glycoside mixture comprising two or more of Reb A
material, Reb B material or Reb D material to help recover at least
one of the Reb A material, Reb B material or Reb D material in more
pure form, comprising the steps of: [0026] a) providing a slurry
comprising glycosides including at least Reb A material, Reb B
material, and Reb D material, wherein the slurry includes a solid
phase and a liquid phase; and [0027] b) aging the slurry at one or
more elevated temperatures independently greater than about
85.degree. C., said aging occurring for a time period and under
conditions sufficient for at least one of (i) the solid phase to
become more pure with respect to Reb A material relative to at
least one of Reb B material and D material; and/or (ii) the liquid
phase to become more pure with respect to at least one of Reb B
material and D material relative to Reb A material.
[0028] In another aspect, the present invention relates to a method
of treating a glycoside mixture comprising two or more of Reb A
material, Reb B material or Reb D material to help recover at least
one of Reb A material, Reb B material or Reb D material in more
pure form, comprising the steps of: [0029] a) providing a slurry
comprising glycosides including at least rebaudioside A material, B
material and D material, wherein the slurry includes a solid phase
and a liquid phase; [0030] b) aging the slurry at one or more
elevated temperatures independently greater than about 40.degree.
C., said aging occurring for a time period sufficient for at least
one of the solid phase and/or the liquid phase to become more pure
with respect to at least one of the rebaudioside A material, B
material and D material; and [0031] c) during at least a portion of
the aging, agitating the heated slurry and causing successive
portions of the heated slurry to contact a cooling surface.
[0032] In another aspect, the present invention relates to a method
of treating a glycoside mixture comprising two or more of Reb A
material, Reb B material or Reb D material to help recover Reb A
material in more pure form, comprising the steps of: [0033] a)
providing a first slurry comprising glycosides including at least
rebaudioside A material, B material and D material, wherein the
first slurry includes a solid phase and a liquid phase, said liquid
phase comprising a first solvent; [0034] b) aging the first slurry,
said aging occurring for a time period sufficient for the solid
phase to become more pure with respect to Reb A material; [0035] c)
incorporating at least a portion of the solid phase obtained in
step (b) into a second slurry, wherein the second slurry includes a
solid phase and a liquid phase, said liquid phase comprising a
second solvent having a different composition than the first
solvent; and [0036] d) aging the second slurry, said aging
occurring for a time period sufficient for the solid phase to
become more pure with respect to Reb A material.
[0037] In another aspect, the present invention relates to a method
of treating a glycoside mixture comprising two or more of Reb A
material, Reb B material or Reb D material to help recover at least
one of Reb B material or Reb D material in more pure form,
comprising the steps of: [0038] a) providing a first slurry
comprising glycosides including at least rebaudioside A material, B
material and D material, wherein the first slurry includes a solid
phase and a liquid phase, said liquid phase comprising a first
solvent; [0039] b) aging the first slurry, said aging occurring for
a time period sufficient for the liquid phase to become more pure
with respect to at least one of Reb B material or Reb D material;
[0040] c) incorporating at least a portion of the liquid phase
obtained in step (b) into a second slurry, wherein the second
slurry includes a solid phase and a liquid phase, said liquid phase
comprising a second solvent having a different composition than the
first solvent; and [0041] d) aging the second slurry, said aging
occurring for a time period sufficient for the liquid phase of the
second slurry to become more pure with respect to at least one of
Reb B material or Reb D material.
[0042] In another aspect, the present invention relates to a method
of purifying an impure rebaudioside A composition, the method
comprising the steps of: [0043] a) providing an impure rebaudioside
A composition comprising rebaudioside A material and at least one
impurity selected from the group consisting of rebaudioside B
material and rebaudioside D material, wherein at least a portion of
the rebaudioside A material is in a first crystalline form; [0044]
b) converting at least a portion of the rebaudioside A composition
from the first form into a second crystalline form; and [0045] c)
converting at least a portion of the second crystalline form of the
rebaudioside A composition to a third crystalline form said third
crystalline form optionally being the same as the first crystalline
form.
[0046] In another aspect, the present invention relates to a method
of treating a glycoside mixture comprising Reb A material and at
least one of stevioside material, Reb B material or Reb D material
to help recover Reb A material in more pure form, comprising the
steps of: [0047] a) providing a slurry comprising glycosides
including at least stevioside, rebaudioside A material, B material
and D material, wherein the slurry includes a solid phase and a
liquid phase, and wherein the slurry includes less than about 60
weight percent Reb A material based on the total weight of
glycosides in the slurry and wherein the liquid phase comprises
ethanol; and [0048] b) aging the slurry at one or more elevated
temperatures independently greater than about 85.degree. C., said
aging occurring for a time period and under conditions sufficient
for the solid phase to become more pure with respect to Reb A
material relative to at least one of stevioside, Reb B material and
D material.
[0049] The purified glycoside compositions purified in accordance
with the present invention are useful in sweetener compositions and
in sweetened food and beverage compositions. Examples of food and
beverage compositions include carbonated beverages, non-carbonated
beverages (e.g., sports drinks and dry beverage mixes), ice cream,
chewing gum, candy, juices, jams, jellies, peanut butter, yogurt,
or cold cereal.
BRIEF DESCRIPTION OF THE FIGURES
[0050] FIG. 1 is the chemical structure of rebaudioside A.
[0051] FIG. 2 is the chemical structure of rebaudioside B.
[0052] FIG. 3 is the chemical structure of rebaudioside D.
[0053] FIG. 4a is a powder X-ray diffraction pattern for an ethanol
crystal form of rebaudioside A useful in the present invention.
[0054] FIG. 4b is a peak listing of a powder X-ray diffraction
pattern for an ethanol crystal form of rebaudioside A useful in the
present invention.
[0055] FIG. 5a is a powder X-ray diffraction pattern for a water
crystal form of rebaudioside A useful in the present invention.
[0056] FIG. 5b is a peak listing of a powder X-ray diffraction
pattern for a water crystal form of rebaudioside A useful in the
present invention.
DETAILED DESCRIPTION
[0057] The embodiments of the present invention described below are
not intended to be exhaustive or to limit the invention to the
precise forms disclosed in the following detailed description.
Rather, the embodiments are chosen and described so that others
skilled in the art may appreciate and understand the principles and
practices of the present invention. All patents, pending patent
applications, published patent applications, and technical articles
cited herein are incorporated herein by reference in their
respective entireties for all purposes.
[0058] The present invention provides methods for treating
glycoside mixtures containing rebaudiosides A, B, and D,
derivatives of one or more of these, and/or synthetic counterparts
of one or more of these natural and/or derivative forms, to recover
at least one of these glycosides in more pure form relative to the
starting mixture. In addition to these glycosides, the mixtures
optionally may include one or more other glycosides. Exemplary
other glycosides include the steviol glycosides, derivatives of
these, or synthetic counterparts. Mixtures of Reb A, B, and D
obtained from natural sources also tend to include the other
steviol glycosides.
[0059] The present invention is particularly useful for obtaining
Reb A material in more pure form from these mixtures relative to at
least Reb B material and D material. Thus, a purified composition
obtained using principles of the present invention may have a
larger percentage of Reb A material and a smaller percentage of Reb
B material and/or D material than the starting mixture. Thus, in
one aspect, the present invention provides methods for the removal
of impurities such as rebaudioside B and rebaudioside D from impure
rebaudioside A compositions.
[0060] Because the principles of the present invention can be used
to separate Reb A material on the one hand from Reb B material
and/or D material on the other hand, a purified composition
obtained using principles of the present invention may have a
larger percentage of Reb B material and/or D material and a smaller
percentage of Reb A material than the starting mixture. Thus, in
another aspect, the present invention provides methods for the
removal of impurities such as Reb A from impure Reb B and/or D
compositions.
[0061] As used herein, the term "rebaudioside A" or "Reb A" refers
to a compound having the chemical structure shown in FIG. 1. As
used herein, the term "material" used with respect to a glycoside
refers to that glycoside, derivative(s) of that glycoside, or
synthetic counterpart(s) of the glycoside or its derivative(s).
Thus, "Reb A material" refers to Reb A, Reb A derivative(s), and/or
synthetic counterpart(s) of Reb A or Reb A derivative(s).
[0062] As used herein in the detailed description the term
"rebaudioside B" or "Reb B" refers to a compound having the
chemical structure shown in FIG. 2. As used herein, "Reb B
material" refers to Reb B, Reb B derivative(s), and/or synthetic
counterpart(s) of Reb B or Reb B derivative(s).
[0063] As used herein in the detailed description the term
"rebaudioside D" or "Reb D" refers to a compound having the
chemical structure shown in FIG. 3. As used herein, "Reb D
material" refers to Reb D, Reb D derivative(s), and/or synthetic
counterpart(s) of Reb D or Reb D derivative(s).
[0064] As used herein, a derivative of a glycoside molecule refers
to a glycoside product that results from a modification of the
glycoside by removing one or more moieties, adding one or more
moieties, substituting one or more moieties for one or more other
moieties, masking one or more moieties, adding or removing
unsaturation, causing unsaturation to be at another location in the
molecule, combinations of these, and the like; provided, however,
that a derivative shall not include those molecules having
modification(s) that change (e.g., increase or decrease) the number
of sugar units in a carbohydrate portion that was, is, or becomes
linked to the aglycone portion of the glycoside or that substitute
one kind of sugar unit (e.g., a mannose unit in a representative
circumstance) for another kind of sugar unit (e.g., a glucose unit
in a representative circumstance). Derivatives do include
modifications to the sugar unit(s), if any, that are present if the
type and number of such sugar units does not change as a result of
the modification.
[0065] For example, adding a sugar moiety to the Reb A carbohydrate
portion that is linked to the aglycone via the natural ester
linkage converts the Reb A to Reb D. The carbohydrate chain there
is increased from one sugar unit to two sugar units. Such a
modification yields Reb D, not a derivative of Reb A. Similarly,
removing such sugar moiety from Reb A yields Reb B rather than a
Reb A derivative where there is no longer a carbohydrate chain at
such location.
[0066] A synthetic counterpart refers to a molecule that is
substantially the same as a natural glycoside or a derivative of a
natural glycoside except the counterpart is obtained via chemical
synthesis rather than being obtained from a natural source. The
stereochemistry of synthetic molecules may be the same or different
than that of the natural counterpart. Where there are multiple
chiral centers, some of these may be the same while others are
different as between the synthetic and natural counterparts. The
glycosides of the mixture can be provided in a variety of
morphological and physical forms. For instance, the glycosides
independently can be provided in crystalline, partially
crystalline, and/or amorphous forms. Glycosides can be supplied in
dry form or can be supplied as a constituent of a paste, slurry, or
the like. In other instances, the glycosides can be at least
partially dissolved and supplied in solutions, gels or the
like.
[0067] In one mode of practice, at least a portion of the
glycosides are crystalline and are provided in an alcohol
crystalline form. Generally, this means that a glycoside has been
crystallized in a liquid carrier including at least 80%, even at
least 90%, even at least 95%, or even at least substantially 100%
of one alcohol such as methanol, ethanol, ispropanol, n-butanol,
combinations of these, and the like. Water is an exemplary
co-solvent in such modes of practice. Aqueous alcohols desirably
include at least about 80 weight percent, even at least about 90
weight percent, or even at least about 95 weight percent of
alcohol(s). In some embodiments the ethanol that is used to prepare
the slurry comprises 190 proof ethanol (i.e., 93-95 weight percent
ethanol). Other grades of ethanol (e.g., 180 proof or 200 proof
ethanol) may also be useful.
[0068] Ethanol crystalline forms are preferred, particularly in
embodiments in which it is desired to obtain Reb A material in more
pure form relative to Reb B material and Reb D material that might
be in a starting mixture. Data has shown that the purity of the Reb
A is higher when the treatment is applied to a glycoside mixture in
which at least a portion of the Reb A is in an ethanol crystalline
form. In other modes of practice, at least a portion of the
glycosides are provided in a water crystalline form. Generally,
this means that a glycoside has been crystallized in a liquid
carrier including at least 80%, even at least 90%, even at least
95%, or even at least substantially 100% water.
[0069] Non-limiting examples of useful ethanol and water crystal
foil is are described in commonly assigned U.S. Provisional
Application Ser. No. 61/168,072, filed Apr. 9, 2009, and entitled
"SWEETENER COMPOSITION COMPRISING HIGH SOLUBILITY FORM OF
REBAUDIOSIDE A AND METHOD OF MAKING" and its published counterpart
PCT Pub. No. WO 2010/118218A1, each of these disclosures being
independently incorporated herein by reference in its respective
entirety.
[0070] The crystalline form of a glycoside can differ depending
upon the nature of the liquid carrier in which the glycoside was
crystallized. For instance, the alcohol crystalline form of Reb A
differs from the water crystalline faun of Reb A. The ethanol
crystal form may be characterized, for example, by having an X-ray
diffraction pattern as shown in FIG. 4a. The water crystal form may
be characterized, for example, by having an X-ray diffraction
pattern as shown in FIG. 5a.
[0071] In some modes of practice, the principles of the present
invention are applied to successive crystalline forms of the
glycoside(s). Thus, the principles of the present invention may be
applied to glycosides in a first stage of processing in which at
least a portion of the glycosides are in a first crystalline form.
By way of example, at least a portion of the glycosides are in an
ethanol crystalline form in such first stage. In a subsequent
processing stage, the principles of the present invention are then
applied to the glycosides when at least a portion of the glycosides
are in a second crystalline form. By way of example, at least a
portion of the glycosides are in a water crystalline form in such
subsequent stage. The first and/or second stages may be repeated as
desired.
[0072] Those modes of practice in which the principles of the
present invention are applied to successive crystalline forms of
the glycoside(s) are referred to herein as form transition
purification. This terminology indicates that the crystalline form
of the glycoside(s) undergoes at least one crystalline form
transition during the course of the treatment. Data has shown that
the purity of a glycoside product such as Reb A is enhanced when
incorporating form transition strategies into a purification
treatment. Without wishing to be bound, it is believed that the
enhancement arises because a crystalline glycoside dissolves in a
liquid carrier and then re-crystallizes in the new crystalline form
in the course of the transition. Hence, any impurities or other
ingredients incorporated into a crystalline lattice are more easily
released and/or separated as the crystal dissolves as compared to a
mechanism in which the crystalline transition were to occur from
one solid phase directly to another solid phase.
[0073] Exemplary modes of practice incorporating form transition
purification are described further below including in the
Examples.
[0074] According to the present invention, the glycoside mixture to
be treated is incorporated into a slurry including at least one
solid phase and at least one liquid phase. The solid phase(s) can
be amorphous and/or crystalline. The slurry generally is obtained
from ingredients that include at least the mixture to be treated
and a suitable liquid carrier.
[0075] The amount of the glycoside mixture incorporated into the
slurry can vary over a wide range. The concentration of the
glycoside mixture in the slurry may be varied to affect the rate of
purification. For instance, the removal of rebaudioside B and
rebaudioside D from an impure rebaudioside A composition is
impacted by this concentration. Generally speaking, as the
concentration of the slurry increases (i.e., higher dissolved
solids) the rate of separation of Reb A material on the one hand
from Reb B material and Reb D material on the other hand tends to
decrease. Having too much solids content also can make it more
difficult to stir and filter the slurry during the course of the
treatment. Yet, throughput, cost, and efficiency are reduced if the
solids content is too low. Balancing such practical concerns,
illustrative slurry embodiments include from about 5 weight percent
to about 50 weight percent, preferably about 10 weight percent to
about 40 weight percent, more preferably about 15 weight percent to
about 30 weight percent of the glycosides based on the total weight
of the slurry.
[0076] The slurry is heated to at least one elevated temperature
above ambient temperature and is allowed to age at the elevated
temperature(s). The aging occurs for a time period sufficient for
at least one of (i) the crystalline phase to become more pure with
respect to at least one of the glycosides (such as Reb A material)
and/or (ii) the liquid phase to become more pure with respect to at
least one of the other glycosides (such as at least one of Reb B
material or D material). Longer aging tends to provide more
purification. Thus, longer aging of the slurry increases the extent
of removal of rebaudioside B material and rebaudioside D material
from an impure rebaudioside A composition. The duration of aging is
mainly subject to practical limits. For instance, after some
duration, the amount of further purification that occurs slows down
too much to be economically practical. Balancing such concerns in
some embodiments, the slurry is aged for a period of time ranging
from about 1 hour or greater, for example, from about 1 hour to
about 24 hours. In a preferred aspect, the slurry is aged for a
period of time ranging from about 3 to about 8 hours, or even about
4 to about 6 hours.
[0077] The liquid carrier desirably includes water, an alcohol, or
a combination of these. Exemplary alcohols include methanol,
ethanol, isopropanol, n-propanol, n-butanol, isobutanol, t-butanol,
combinations of these, and the like. The alcohol(s) may be aqueous
as discussed herein. In some embodiments the ethanol that is used
to prepare the slurry comprises 190 proof ethanol (i.e., 93-95
weight percent ethanol). Other grades of ethanol (e.g., 180 proof
or 200 proof ethanol) may also be useful.
[0078] The treatment may occur at a wide range of elevated
temperatures. Desirably, boiling and reflux of the liquid carrier
are avoided. Heat increases the rate and extent of separation of
rebaudioside B material and rebaudioside D material from
rebaudioside A material. Without wishing to be bound by theory, it
is believed that one or more of the glycosides undergo
conformational or other transformations that favor separation. In
such embodiments, the slurry is heated at a temperature of at least
about 40.degree. C. to, preferably at least about 50.degree. C.,
more preferably at least about 70.degree. C., and even more
preferably at least about 95.degree. C. Heating desirably occurs up
to a temperature of about 200.degree. C., preferably 150.degree.
C., more preferably 120.degree. C. In one mode of practice, heating
at 100.degree. C. is suitable.
[0079] When the mixture is well mixed, the bulk temperature
generally is uniform throughout the mixture. In such well-mixed
mixtures, the bulk temperature desirably is in such temperature
ranges. When the mixture is not well-mixed such that a temperature
gradient exists, then at least a portion, desirably at least about
5 volume percent, more desirably at least about 30 volume percent,
more desirably at least about 50 volume percent of the mixture has
temperature(s) in such temperature ranges.
[0080] The treatment may occur under a range of pressures. For
instance, the treatment may occur under ambient pressure or
elevated pressure(s) greater than ambient pressure. Elevated
pressures allow the slurry to be heated at higher temperatures
while staying below the boiling point of the liquid at the elevated
pressure. Exemplary absolute pressures range from ambient pressure
to about 30 atm, even about 1.1 atm to about 30 atm, preferably
about 1.1 atm to about 15 atm, more preferably about 1.1 atm to
about 10 atm, and even more preferably from about 1.1 atm to about
5 atm. In some modes of practice using liquid carriers comprising
at least 90 weight percent ethanol in water, using a pressure of
about 3 atm is suitable. Elevated pressures allow the use of higher
temperatures in those embodiments in which it is desirable that the
pressure is higher than the vapor pressure of the solvent at the
desired temperature. This is desirable in that higher temperatures
generally lead to better resolution among glycosides. For example,
higher temperatures generally provide better resolution between Reb
A material on one hand and Reb B material and D material on the
other hand.
[0081] In some embodiments the slurry is agitated during treatment.
Agitation generally increases the degree of purification. For
example, agitation of a slurry comprising Reb A material, B
material, and D material increases the rate and extent of
separation of rebaudioside B material and rebaudioside D material
from the rebaudioside A material. Typically agitation comprises,
for example, mixing at high speed (e.g., 200 rpm) with an impeller
in a baffled mixing vessel (e.g., a 5-liter baffled mixing
vessel).
[0082] As the slurry is aged, the glycoside components are
selectively partitioned between the solid and liquid phases. In the
case of Reb A material, B material and D material, Reb A material
tends to be more favored in the solid phase while Reb B material
and D material are more favored in the liquid phase. This means
more pure Reb A material is obtained in the solid phase, while more
pure Reb B material and D material are in the liquid phase. The
resultant solid phase also comprises crystalline content.
[0083] The two phases are easily separated by a variety of
techniques, including filtration, to recover the desired purified
material. If pure Reb A material is desired, the crystals can be
filtered, washed, dried, further processed, or the like. If Reb B
material and/or D material are desired, the liquid can be processed
to recover the Reb B-material and D material as a dried product, a
dispersion, a solution, or the like. A variety of drying techniques
may be used including spray drying, oven drying, vacuum drying,
combinations of these, and the like.
[0084] In preferred embodiments, the solid and liquid phases
resulting from the treatment are separated by filtering. Desirably,
the product mixture is at a temperature of at least about
50.degree. C., preferably at least about 70.degree. C. during at
least a portion of the filtering. Hot filtration advantageously
enhances separation of Reb B material and Reb D material from Reb A
material in mixtures that include Reb A material, B material, and D
material.
[0085] Without wishing to be bound, it is believed that separation
is more favored at higher temperatures at least in part due to
factors including conformational changes as well as solubility
differences that are a function of temperature. At room
temperature, the solubility of Reb B in a 94 weight percent ethanol
solution saturated with Reb A is about 0.3 g per 100 g of solvent,
and the solubility of Reb D is about 0.01 g per 100 g. At
100.degree. C., concentrations of Reb D as high as 0.2 g/100 g are
observed, and concentrations of Reb B as high as 0.5 g/100 g are
observed. The solubility of Reb A in 94 wt % ethanol varies to a
much smaller extent.
[0086] Aging the slurry at high temperatures thus increases the
concentration of Reb B material and Reb D material in solution, and
correspondingly decreases the Reb B material and Reb D material
amounts in the solid phase. Hot filtration more easily allows the
separation of Reb B material and Reb D material from Reb A material
by separating the solids and liquid while maintaining the higher
solubility of Reb B material and Reb D material. In contrast, cold
filtering might risk precipitation of Reb B material and Reb D
material such that the Reb B material and Reb D material
concentrations in the liquid are closer to the room temperature
solubilities. This can cause more Reb B material and D material to
be in the solid phase, leading to less pure Reb A material in the
solid phase. Thus, cold filtering can undermine purification gains
obtained earlier in the treatment. If it is desired to cool prior
to filtration, the slurry may be cooled only to the extent
necessary. In one instance, cooling from 100.degree. C. to
70.degree. C. prior to filtration maintains the purification of the
method while reducing the risks associated with filtration.
[0087] Although not wishing to be bound by theory, it is believed
that purification occurs at least in part via solvent mediated
crystallization due to the presence of both solid and liquid
phases. In a slurry where solid and liquid phases are present,
crystallization and dissolution occur simultaneously. This means
that, at any one point in time, it might be true that only a
portion of the glycoside(s) are in a crystal phase, while the
remainder tends to be dissolved in the liquid phase. It is
believed, however, that substantially all of the available
glycoside(s) participate in dissolution and crystallization such
that differing portions of the glycosides are continuously
precipitating into one or more insoluble states while other
portions are being converted into one or more soluble states. In
short, while only some of the glycoside might be in one phase or
the other at any one point in time, substantially all of the
glycoside crystallizes and dissolves repeatedly over time. As
successive portions are dissolved and crystallized, the
partitioning between the phases, and hence the purity, becomes
enhanced. The process is dynamic and can lead to changes in purity
and shape over time.
[0088] In some embodiments, the dissolution and the crystallization
occur generally at substantially equal rates such that there is
very little if any net change in the macroscopic partition between
the two phases. That is, molecules in the crystalline phase
dissolve and molecules in the liquid phase can crystallize at
substantially equal rates.
[0089] In some embodiments, particularly when the mixture is
agitated during heat treatment, it is desirable if the heat
treatment occurs in the presence of one or more cooling surfaces
that are at a temperature that is less than the bulk temperature of
the mixture being treated. Thus, as the mixture is agitated and
thereby mixed during the course of the heat treatment, successive
portions of the mixture will be in contact with the cooling
surface(s). Even though mixing causes the bulk of the mixture to
generally be at a uniform bulk temperature, heating the mixture in
the presence of such cooling surface(s) has been found to enhance
the purification. In contrast, merely subjecting the heated mixture
to repeated cycles of heating and cooling has not been observed to
provide the same purification enhancement.
[0090] Without wishing to be bound, a potential theory to explain
the benefit of heating in the presence of a cooling surface can be
suggested. The presence of both hot and cold surfaces in the
mixture tends to favor crystallization near the cold surfaces but
dissolution near the hot surfaces or in the hotter bulk mixture. By
maintaining a cold surface in the mixture, crystallization and
dissolution happen more frequently as crystals are convected from
the cold zone to the hot zone, leading to higher purification at
least for crystalline starting materials. The presence of both hot
and cold surfaces also leads to larger particle sizes when using
either crystalline or amorphous starting materials because smaller
particles more rapidly dissolve due to a higher surface area to
volume ratio. The higher purification may alternatively be due to
the decreased fraction of small crystals in the mixture. It is also
believed that using cold surfaces in the hot mixture may also
increase the rate of purification for both amorphous and
crystalline starting materials.
[0091] Generally, the cooling surface(s) are at one or more
temperature(s) below about 40.degree. C., preferably about
35.degree. C. or less, even about 30.degree. C. or less. Cooling
surfaces can be provided in a variety of ways. In one embodiment, a
cooling surface is provided by the surface of a coil that is
immersed in the mixture and through which a cooling fluid flows. In
such a mode of practice, the fluid might enter the immersed portion
of the coil at an initial temperature, e.g., about 30.degree. C. or
less, even about 20.degree. C. or less or even about 15.degree. C.
or less and exit the immersed portion of the coil at a moderately
higher temperature due to heat transfer, such as about 5.degree. C.
or more warmer, even 10.degree. C. or more wanner, or even
15.degree. C. or more warmer. In another embodiment, the cooling
surface is provided by an external heat exchanger, through which a
portion of the slurry, drawn from and returning to the heating
vessel, is circulated.
[0092] In a preferred embodiment of this aspect, the slurry can be
heated under greater than ambient pressure as described above in
order to more easily allow the treatment to occur at higher
temperatures. It has been found that carrying out the treatment at
higher temperatures under elevated pressure enhances the resolution
between Reb A on the one hand and Reb B and D on the other
hand.
[0093] Typically, the glycoside mixture that is used as a starting
material in the method of the invention comprises a major amount of
rebaudioside A material. A major amount means at least about 20
weight percent. Typically, the glycoside mixture may include from
about 20 weight percent to about 96, preferably about 30 to about
96, more preferably about 40 to about 96 weight percent of Reb A
material based on the total weight of glycosides. The total amount
of both rebaudioside B material and rebaudioside D material in the
mixture can vary. In many embodiments, the total amount of Reb B
material and D material is up to about 6 weight percent based on
the total weight of the glycosides. For example, in some
embodiments the mixture comprises about 90 weight percent to about
96 weight percent rebaudioside A; about 1 weight percent to 4
weight percent rebaudioside B; and about 1 weight percent to about
4 weight percent rebaudioside D. A crystalline product obtained
using the principles of the present invention may include at least
about 80 weight percent, even at least about 90 weight percent, or
even at least about 96 weight percent of Reb A.
[0094] It is quite advantageous that the present invention can be
used to enhance the purity of Reb A material within glycoside
mixtures containing about 60 weight percent or less, even 45 weight
percent or less, or even 30 weight percent or less of Reb A
material, particularly when the amount of stevioside material in
such mixtures is at least about 10 weight percent of the total
glycosides, or even at least about 20 weight percent of the total
glycosides, or even greater than the amount of Reb A material in
some embodiments. Reb A material in such compositions may be
crystalline or amorphous, but often is at least partially
amorphous. In many conventional processes when Reb A material is
present in glycoside mixtures at such lower content levels, Reb A
material is too soluble in solvents such as water or ethanol to be
adequately crystallized and purified. Desirably, the liquid phase
of the slurry(ies) used in such embodiments includes ethanol,
desirably at least about 80 weight percent ethanol, or even at
least about 90 weight percent ethanol, or even at least about 95
weight percent of ethanol based on the total weight of solvent
incorporated into the slurry.
[0095] Without wishing to be bound, it is believed that such
mixtures, particularly when obtained from natural sources, tend to
include relatively greater amounts of stevioside material. The
stevioside material tends to solubilize the Reb A material. The
solvent mediated crystallization treatment of the invention,
optionally in combination with transition crystallization, is able
to selectively partition Reb A material into a crystalline phase
notwithstanding the solubilizing effects of stevioside material
that otherwise would be expected to be a technical obstacle based
on conventional experiences. Without wishing to be bound by theory,
it is believed that elevated temperatures, particularly at
85.degree. C. or higher, preferably 90.degree. C. or higher, more
preferably 100.degree. C. or higher induce conformational changes
in the steviol glycosides that promote crystallization of Reb A
material even in such an unfavorable context.
[0096] It is also quite advantageous that the present invention can
be used to boost the purity or Reb A material that is already
highly pure. For instance, some conventional processes might be
able to produce crystals that include about 90 weight percent to
about 95 weight percent Reb A material. While such crystals are
highly pure with respect to Reb A material pursuant to many
applicable standards, there are other standards in which even more
pure Reb A material is desired. The present invention can be
applied to such crystals to boost the Reb A purity to as much as 96
weight percent, even 96 weight percent to 99 weight percent.
[0097] In one preferred embodiment of the method of the invention,
a 30 weight percent slurry of impure rebaudioside A in 190 proof
ethanol is heated to 70.degree. C. and is held for about one hour
with agitation. Following this, a retentate product including
rebaudioside A crystals is recovered by filtration, and the
retentate is washed with 190 proof ethanol (e.g., about 2 cake
weights of solvent). The method results in the removal of about 30%
rebaudioside B and about 50% rebaudioside D from the impure
rebaudioside A composition. The yield of rebaudioside A is
typically about 95 weight percent.
[0098] In another preferred embodiment of the method of the
invention, a 30 weight percent slurry of impure rebaudioside A in
190 proof ethanol is heated to 70.degree. C. and is held for about
24 hours with agitation. Following this, a retentate product
including the rebaudioside A crystals is recovered by filtration
and the retentate is washed with 190 proof ethanol (e.g., about 2
cake weights of solvent). The method results in the removal of
about 50% rebaudioside B and about 50% rebaudioside D from the
impure rebaudioside A composition. The yield of rebaudioside A is
typically about 95 weight percent.
[0099] A representative purified rebaudioside A composition
typically comprise about 97 weight percent or greater rebaudioside
A material; about 2 weight percent or less rebaudioside B material;
and about 2 weight percent or less rebaudioside D material. Other
components that may be included in the purified rebaudioside A
composition include, for example, stevioside material, rebaudioside
C material, and rebaudioside F material.
[0100] Particularly preferred aspects of the present invention
involve separating (also referred to as resolving) Reb A material
on the one hand from Reb B material and/or D material on the other
hand. In one such aspect, the present invention provides a method
of purifying an impure rebaudioside A composition using effects
that are believed to occur at least in part to solvent mediated
crystallization. The impure rebaudioside A composition comprises at
least one impurity selected from rebaudioside B material and
rebaudioside D material. Desirably, at least the Reb A material is
in an ethanol crystalline form.
[0101] In other embodiments, the Reb A material may be in other
crystal forms and/or may be amorphous. The method comprises the
steps of: (a) providing an impure rebaudioside A composition
comprising rebaudioside A material and at least one impurity
selected from rebaudioside B material and rebaudioside D material;
(b) preparing a slurry of the impure rebaudioside A composition in
a suitable liquid carrier such as ethanol; (c) aging the slurry for
a period of time of about 1 hour or greater; (d) optionally,
heating the slurry during at least a portion of the aging such as
to a temperature of about 45.degree. C. to about 100.degree. C.;
(e) optionally, agitating the slurry during at least a portion of
the aging; and (f) after the aging step, filtering the slurry to
collect the crystals (retentate) including the purified Reb A
material, and washing the retentate to provide a purified
rebaudioside A composition. In the purified rebaudioside A
composition at least a portion of at least one of the impurities
has been reduced as compared to the impure rebaudioside A
composition.
[0102] In some aspects, the invention provides a method of
purifying glycoside mixtures, such as an impure rebaudioside A
composition, that incorporates form transition purification. In
such embodiments, a glycoside mixture is provided wherein at least
one glycoside is in a first crystalline form. For example, an
impure rebaudioside A composition may be provided that comprises
rebaudioside A material and at least one impurity selected from the
group consisting of rebaudioside B material and rebaudioside D
material. At least the Reb A material is in a first crystalline
form such as an ethanol crystalline form. The ethanol crystalline
form can be aged in a slurry as described above to enhance purity
of the crystals with respect to Reb A material. The mixture is then
treated to convert the glycoside into a second crystalline form.
For example this may involve converting the rebaudioside A material
from an ethanol crystalline form into a water crystalline form. The
water crystalline form can be aged in a slurry as described above
to enhance purity of the crystals with respect to Reb A material.
Then, the water crystalline form of the rebaudioside A material can
be converted from the water crystalline form to an ethanol
crystalline form. Again, this form can be aged in a slurry as
described above to enhance purity. This series of conversions helps
to provide a purified rebaudioside A composition having a reduced
amount of at least one impurity selected from rebaudioside B
material and rebaudioside D material.
[0103] In some embodiments, the step of converting the ethanol
crystal form to the water crystal form comprises: (a) combining the
rebaudioside A composition with water to form a water-based slurry;
and (b) allowing the water-based slurry to stand for a period of
time sufficient to convert the ethanol crystalline form to a water
crystalline form. The water crystalline form may be described as a
four-hydrate polymorph of rebaudioside A. In some embodiments, the
step of converting the water crystal form to the ethanol crystal
form comprises: (a) combining the rebaudioside A composition with
ethanol to form an ethanol-based slurry; and (b) allowing the
ethanol-based slurry to stand for a period of time sufficient to
convert the water crystal form to an ethanol crystalline form. The
solids content, solvent characters, agitation, temperatures,
pressures can be selected as described above with respect to the
solvent mediated crystallization techniques. However, the ethanol
used to convert the water form to the ethanol form typically
comprises greater than about 93 weight percent ethanol although
other concentrations may also be used.
[0104] The form transition purification results in the removal of
rebaudioside B material, rebaudioside D material, or both from the
impure rebaudioside A composition (i.e., the starting material). In
some embodiments, the form transition results in the removal of up
to about 50% of the rebaudioside B and up to about 95% of the
rebaudioside D that was present in the impure rebaudioside A
composition.
[0105] The principles of the present invention can be used in
combination with other purification strategies. For example, PCT
Pub. No. WO 2008/091547A2 describes a method of purifying
glycosides such as Reb A using solvent/antisolvent/solvent
techniques. The present invention can be used prior to and/or after
such solvent/antisolvent/solvent techniques to obtain purified Reb
A even more effectively and/or efficiently. PCT Pub. No. WO
2008/091547A2 is incorporated herein by reference in its entirety
for all purposes.
[0106] The invention will now be described with reference to the
following non-limiting examples.
EXAMPLE 1
[0107] Each of three samples of glycoside material containing the
90%, 95%, 92% Reb A %, respectively, and 2.9%, 0.1%, 1.0% Reb D,
respectively, and 0.07%, 3.0%, 1.4% Reb B, respectively, in the
ethanol crystalline forms was mixed with water to form a slurry of
13% solids in water. The slurry was agitated overnight at room
temperature with a magnetic stir bar and stir plate, with
sufficient agitation to keep all solid material suspended. After
aging overnight, the material was filtered. The material contained
93%, 95%, and 95% Reb A, respectively; 2.4%, 0%, and 0.6% Reb D,
respectively; and 0.5%, 3.9%, and 2.5% Reb B, respectively. The
material recovered in the solid phase from each treatment was 88%,
98%, and 98%, respectively, of the total material fed to the
process. The filtrate was dried in a vacuum oven, and contained
73%, 79%, 72% Reb A, respectively; 9.6%, 1.8%, 8.4% Reb D,
respectively; and 0.4%, 3.7%, 0.5% Reb B, respectively.
EXAMPLE 2
[0108] Each of the three materials produced in Example 1 was
slurried in pure ethanol in a slurry of 3.3%, 8.8%, 6.0% solids,
respectively, and agitated overnight at room temperature. After the
secondary aging, the material was again filtered, washed with
200-proof ethanol, and dried. Each filtered product contained 99%,
98%, 98% Reb A, respectively, 1.1%, 0.0%, 0.1% Reb D, respectively,
and 0.1%, 1.3%, 1.0% Reb B, respectively. The overall yield of
material in the solid phase, including the step in Example 1, was
64%, 83%, and 73%, respectively. The filtrate was dried in a vacuum
oven, and contained 86%, 49%, 74% Reb A, respectively; 3.0%, 0.36%,
2.6% Reb D, respectively; and 1.6%, 19%, 11% Reb B,
respectively.
EXAMPLE 3
[0109] Each of the three materials produced in Example 1 was
slurried in 190-proof ethanol in a slurry of 6.9%, 4.9%, 7.2%
solids, respectively, and agitated overnight at room temperature.
After the secondary aging, the material was again filtered, washed
with 190-proof ethanol, and dried. Each product contained 99%, 99%,
99% Reb A, respectively, 0.0%, 0.3%, 0.3% Reb D, respectively, and
1.0%, 0.1%, 0.6% Reb B, respectively. The overall yield of material
recovered in the solid phase, including the processing in Example
1, was 68%, 45%, 71%, respectively. The filtrate was dried in a
vacuum oven, and contained 74%, 81%, 73% Reb A, respectively; 10%,
2.3%, 9.7% Reb D, respectively; and 0.5%, 3.5%, 0.5% Reb B,
respectively.
EXAMPLE 4
[0110] Each of three samples of glycoside material containing the
90%, 95%, 92% Reb A %, respectively, and 2.9%, 0.1%, 1.0% Reb D,
respectively, and 0.07%, 3.0%, 1.4% Reb B, respectively, in the
ethanol crystalline forms were processed as in Example 1. The
collected solid material after processing contained 97%, 95%, 95%
Reb A, respectively; 1.1%, 0%, 0.65% Reb D, respectively; and 0.9%,
3.9%, 2.9% Reb B, respectively. Each of the three collected solid
materials was slurried in pure methanol at 5.1%, 6.0%, 5.3% solids,
respectively, and agitated overnight at room temperature. After the
secondary aging, the material was again filtered, washed with pure
methanol, and dried. The product contained 99%, 99%, 99% Reb A,
respectively, 0.2%, 0.0%, 0.2% Reb D, respectively, and 0.2%, 1.3%,
0.7% Reb B, respectively. The overall yield of material recovered
in the solid phase, including the first step processing in water,
was 41%, 64%, 58%. The filtrate was collected and dried in a vacuum
oven, and contained 83%, 79%, 72% Reb A, respectively; 6.5%, 2.7%,
9.6% Reb D, respectively; and 0.5%, 4.0%, 0.4% Reb B,
respectively.
EXAMPLE 5
[0111] Material containing ethanol crystalline forms of 93.4% Reb
A, 2.4% Reb D, and 1.5% Reb B was mixed with 190-proof ethanol to
produce a slurry containing 10% solids. The slurry was agitated at
room temperature. After one hour, a sample of the material was
filtered, washed with 190-proof ethanol, and dried. The sample
contained 96% Reb A, 1.5% Reb D, and 1.6% Reb B. 89% of the
glycoside material in the sample was recovered as a solid phase.
The remaining slurry was held overnight, then filtered, washed with
190-proof ethanol, and dried. After an additional .about.24 hours
in the slurry, the crystalline product from the remaining slurry
contained 96% Reb A, 1.4% Reb D, and 1.4% Reb B, and 89% of the
glycoside material of the remaining slurry was recovered as a solid
phase. The filtrate was collected and dried in a vacuum oven, and
contained 83% Reb A, 10.4% Reb D, and 4.9% Reb B.
EXAMPLE 6
[0112] Material containing ethanol crystalline fauns of 93.4% Reb
A, 2.4% Reb D, and 1.5% Reb B was mixed with 190-proof ethanol to
produce a slurry containing 30% solids. The slurry was heated to
70.degree. C. and agitated. After one hour, a sample was filtered
at 70.degree. C. washed with 190-proof ethanol, and dried. The
sample contained 96% Reb A, 1.8% Reb D, and 1.7% Reb B. 95% of the
glycoside material in the sample was recovered as a solid phase.
The filtrate was collected and dried in a vacuum oven, and
contained 87% Reb A, 7.0% Reb D, and 3.9% Reb B. The slurry
remaining after this sampling was held overnight, then filtered,
washed with 190-proof ethanol, and dried. After an additional
.about.24 hours in the slurry, the crystalline product of the
remaining contained 98% Reb A, 1.3% Reb D, and 0.4% Reb B, and 95%
of the glycoside material was recovered from the remaining slurry
as a solid phase
EXAMPLE 7
[0113] Material containing ethanol crystalline forms of 93.4% Reb
A, 2.4% Reb D, and 1.5% Reb B was mixed with pure ethanol to
produce a slurry containing 30% solids. The slurry was heated to
70.degree. C. and agitated. After one hour, a sample was filtered
at 70.degree. C., washed with pure ethanol, and dried. The sample
contained 95% Reb A, 2.3% Reb D, and 1.5% Reb B, and 97% of the
glycoside material in the sample was recovered as a solid phase.
The filtrate was collected and dried in a vacuum oven, and
contained 73% Reb A, 7.7% Reb D, and 17% Reb B. The remaining
slurry was held overnight, then filtered at 70.degree. C., washed
with 190-proof ethanol, and dried. After an additional .about.24
hours in the slurry, the crystalline product of the remaining
slurry contained 96% Reb A, 2.1% Reb D, and 1.3% Reb B, and 96% of
the glycoside material of the remaining slurry was recovered as a
solid phase.
EXAMPLE 8
[0114] 58 g of amorphous steviol glycosides were placed in 94 wt %
ethanol to produce a slurry with 20% by weight steviol glycosides.
The slurry was placed in a 500 ml pressure vessel at 20 psig with
an agitator and a cooling loop with 58 cm.sup.2 surface area. The
cooling loop was a simple U-loop of stainless steel, about 40 cm in
total length, slightly offset from the center of the vessel to
accommodate an agitator. The vessel was purged with nitrogen. The
slurry was then heated to a bulk temperature of 100.degree. C. over
1 hour and held at 100.degree. C. for 2 hours. Water at 15.degree.
C. was fed to the cooling loop at 60 ml/min. The cooling water
exited the cooling loop at 25.degree. C. The pressure vessel was
agitated at 180 rpm. After the two hour hold at 100.degree., the
mixture was cooled to 70.degree. C. over 30 minutes, filtered in a
Buchner funnel at 70.degree. C., and washed with 57 g of pure
ethanol in the Buchner funnel. The solids were collected, dried,
and analyzed by HPLC. 12 g of material was produced.
TABLE-US-00001 Sample Name Reb D Reb A Stev. Reb F Reb C Dulc. A
Rub. Reb B wt % glycosides 1.1 35.0 39.5 1.2 7.9 0.4 3.4 0.1 of
Feed Material by HPLC wt % glycosides 0.2 91.3 0.5 1.1 5.1 0.2 --
0.1 of solids by HPLC
EXAMPLE 9
[0115] 91 g of amorphous steviol glycosides were placed in 100%
ethanol to produce a slurry with 30% by weight steviol glycosides.
The slurry was placed in a pressure vessel according to Example 8
at 20 psig. The vessel was purged with nitrogen, then the mixture
was heated to a bulk temperature of 100.degree. C. over 1 hour and
held at 100.degree. C. for 2 hours, with flow of 60 ml/min of water
at 15.degree. C. inlet through the cooling loop with agitation of
180 rpm. The outlet temp of the cooling water was 25.degree. C. The
mixture was then cooled to 70.degree. C. over 30 minutes, filtered
at 70.degree. C. in a Buchner funnel, and washed with 63 g of pure
ethanol in the Buchner funnel. The solids were dried, and analyzed
by HPLC. 8 g of material was produced.
TABLE-US-00002 Sample Name Reb D Reb A Stev. Reb F Reb C Dulc. A
Rub. Reb B StevB wt % glycosides 2.4 22.3 19.2 0.9 4.9 0.6 2.3 13.7
5.7 of Feed Material by HPLC wt % glycosides of 0.14 83.14 0.26
1.08 5.05 0.38 -- 3.26 0.19 solids by HPLC
EXAMPLE 10
[0116] 59 g of ethanol crystalline form Steviol glycosides were
placed in 94 wt % ethanol to produce a slurry with 19% by weight
steviol glycosides. The slurry was placed in a pressure vessel
according to Example 8 at 20 psig. The vessel was purged with
nitrogen. The slurry was then heated to a bulk temperature of
100.degree. C. over 1 hour and held at 100.degree. C. for 6 hours
with a flow of 60 ml/min of water at 15.degree. C. inlet through
the cooling loop with agitation at 180 rpm. The outlet temp of the
cooling water was 25.degree.. The mixture was then cooled to
70.degree. C. over 30 minutes, filtered at 70.degree. C. and washed
with 107 g of pure ethanol. The solids were collected, dried, and
analyzed by HPLC. 37 g of material was recovered as product. The
filtrate was collected, dried in a vacuum oven, and analyzed by
HPLC.
TABLE-US-00003 Sample Name Reb D Reb A Stev. Reb F Reb C Dulc. A
Rub. Reb B StevB wt % glycosides 2.8 94.7 0.1 0.2 0.0 -- -- 0.8 --
of Feed Material by HPLC wt % glycosides of 1.7 96.9 -- 0.1 -- --
-- 0.6 -- solids by HPLC wt % glycosides of 8.0 86.4 0.7 0.3 0.1 --
-- 3.7 -- filtrate by HPLC
EXAMPLE 11
[0117] 59 g of amorphous Steviol glycosides were placed in 94 wt %
ethanol to produce a slurry with 19% by weight steviol glycosides.
The slurry was placed in a pressure vessel according to Example 8
at 20 psig. The vessel was purged with nitrogen. The slurry was
then heated to a bulk temperature of 100.degree. C. over 1 hour and
held at 100.degree. C. for 2 hours with a flow of 60 ml/min of
water at 15.degree. C. inlet through the cooling loop and agitation
at 180 rpm. The outlet temp of the cooling water was 25.degree. C.
The mixture was then cooled to 70.degree. C. over 30 minutes,
filtered at 70.degree. C., and washed with 133 g of pure ethanol in
a Buchner funnel. The solids were collected and analyzed by HPLC.
35 g of material was produced. The filtrate was collected, dried in
a vacuum oven, and analyzed by HPLC.
TABLE-US-00004 Sample Name Reb D Reb A Stev. Reb F Reb C Dulc. A
Rub. Reb B StevB wt % glycosides of 2.3 81.6 7.1 0.6 2.3 0.1 -- 2.1
0.2 Feed Material by HPLC wt % glycosides of 1.7 92.6 1.5 1.2 0.4
-- -- 1.0 -- solids by HPLC wt % glycosides of 3.4 42.6 30.6 1.1
5.1 1.0 -- 8.3 2.7 solids by HPLC
EXAMPLE 12
[0118] 60 g of amorphous Steviol glycosides were placed in pure
ethanol to produce a slurry with 19% by weight steviol glycosides.
The slurry was placed in a pressure vessel according to Example 8
at 20 psig. The vessel was purged with nitrogen. The slurry was
then heated to a bulk temperature of 100.degree. C. over 1 hour and
held at 100.degree. C. for 2 hours with agitation at 180 rpm and
with flow of 60 ml/min of water at 15.degree. C. inlet through the
cooling loop. The outlet temp of the cooling water was 25.degree.
C. The mixture was then cooled to 70.degree. C., filtered at
70.degree. .degree. C., and washed with 148 g of pure ethanol. The
solids were collected and analyzed by HPLC. 46 g of material was
produced. The filtrate was collected, dried in a vacuum oven, and
analyzed by HPLC.
TABLE-US-00005 Sample Name Reb D Reb A Stev. Reb F Reb C Dulc. A
Rub. Reb B StevB wt % glycosides of 2.3 81.6 7.1 0.6 2.3 0.1 -- 2.1
0.2 Feed Material by HPLC wt % glycosides of 2.2 88.3 3.5 0.5 1.7
-- -- 1.5 -- solids by HPLC wt % glycosides of 4.9 24.3 38.4 1.1
5.9 1.7 -- 8.4 2.7 filtrate by HPLC
EXAMPLE 13
Example without Cooling
[0119] 86 g of alcohol crystalline Steviol glycosides were placed
in 190-proof ethanol to produce a slurry with 19% by weight steviol
glycosides. The slurry was placed in a pressure vessel according to
Example 8 at 20 psig. The vessel was purged with nitrogen. The
slurry was then heated to 100.degree. C. over 1 hour and held at
100.degree. C. for 2 hours without cooling water flowing through
the cooling loop. The vessel was agitated at 180 rpm. The mixture
was then cooled to 70.degree. C., filtered at 70.degree. C., and
washed with 216 g of pure ethanol. The solids were collected and
analyzed by HPLC. 75 g of material was produced. The filtrate was
collected and dried and analyzed by HPLC.
TABLE-US-00006 Sample Name Reb D Reb A Stev. Reb F Reb C Dulc. A
Rub. Reb B StevB wt % glycosides of 1.9 95.8 -- 0.1 0.1 -- -- 0.9
-- Feed Material by HPLC wt % glycosides of 1.5 97.1 -- 0.1 -- --
-- 0.4 -- solids by HPLC wt % glycosides of 6.4 63.8 1.7 0.8 -- 0.1
-- 18.8 -- filtrate by HPLC
EXAMPLE 14
Example with Cooling
[0120] 86 g of alcohol crystalline Steviol glycosides were placed
in 190-proof ethanol to produce a slurry with 19% by weight steviol
glycosides. The slurry was placed in a pressure vessel according to
Example 8 at 20 psig. The vessel was purged with nitrogen. The
slurry was then heated to 100.degree. C. over 1 hour and held at
100.degree. C. for two hours with flow of 60 ml/min of water at
15.degree. C. inlet through the cooling loop. The outlet temp of
the cooling water was 25.degree. C. The vessel was agitated at 180
rpm. The mixture was then cooled to 70.degree. C., filtered at
70.degree. C., and washed with 216 g of pure ethanol. The solids
were collected and analyzed by HPLC. 75 g of material was produced.
The filtrate was collected and dried and analyzed by HPLC.
TABLE-US-00007 Sample Name Reb D Reb A Stev. Reb F Reb C Dulc. A
Rub. Reb B StevB wt % glycosides of 1.9 95.8 -- 0.1 0.1 -- -- 0.9
-- Feed Material by HPLC wt % glycosides of 1.0 97.8 -- 0.1 -- --
-- 0.3 -- solids by HPLC wt % glycosides of 7.2 67.4 1.3 0.9 0.2
0.1 -- 15.7 -- filtrate by HPLC
[0121] Other embodiments of this invention will be apparent to
those skilled in the art upon consideration of this specification
or from practice of the invention disclosed herein. Various
omissions, modifications, and changes to the principles and
embodiments described herein may be made by one skilled in the art
without departing from the true scope and spirit of the invention
which is indicated by the following claims. All patents, patent
documents, and publications cited herein are hereby incorporated by
reference as if individually incorporated.
* * * * *