METHOD OF EXTRACTING SELECTED SWEET GLYCOSIDES FROM THE STEVIA REBAUDIANA PLANT

METHODE POUR L'EXTRACTION DE GLYCOSIDES SELECTIONNES A PARTIR DE LA PLANTE STEVIA REBAUDIANA

English Abstract

A method of extracting selected sweet glycosides from the
stevia rebaudiana plant. Firstly, extracting a liquid solution
of mixed sweet glycosides from the stevia rebaudiana plant
using a water soluble organic solvent. Secondly, crystallizing
the liquid solution of sweet glycosides to obtain a
crystallized solid containing a higher concentration of a
selected sweet glycoside and a waste liquor containing other
sweet glycosides.

French Abstract

Méthode d'extraction de certains glucosides édulcorants de Stevia rebaudiana. On extrait d'abord une solution liquide d'un mélange de glucosides édulcorants de Stevia rebaudiana au moyen d'un solvant organique hydrosoluble. On la cristallise ensuite afin d'obtenir un solide cristallisé contenant une forte concentration en certains glucosides édulcorants et un liquide résiduel contenant d'autres glucosides édulcorants.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of extracting selected sweet glycosides from the
stevia rebaudiana plant, comprising the steps of:
firstly, extracting a liquid solution of mixed sweet
glycosides from the stevia rebaudiana plant; and
secondly, crystallizing the liquid solution of sweet
glycosides to obtain a crystallized solid containing a higher
concentration of a selected sweet glycoside and a waste liquor
containing other sweet glycosides.

2. The method as defined in Claim 1, including further steps
of:
thirdly, dissolving the crystallized solid containing a
higher concentration of the selected sweet glycoside using a
water soluble organic solvent to obtain a sweet liquor of the
selected sweet glycoside; and
fourthly, crystallizing the sweet liquor of the selected
sweet glycoside to obtain a second crystallized solid
containing an even higher concentration of the selected sweet
glycoside and a second waste liquor containing other sweet
glycosides.

3. The method as defined in Claim 2, having the further steps
of repeating steps three and four until a final crystallized
solid of desired purity of the selected sweet glycoside is
obtained.

4. The method as defined in Claim 2, the water soluble organic
solvent being a methanol solution.



5. A method of extracting selected sweet glycosides from the
stevia rebaudiana plant, comprising the steps of:
firstly, extracting a liquid solution of mixed sweet
glycosides from the stevia rebaudiana plant;
secondly, removing impurities from the liquid solution of
sweet glycosides by passing the liquid solution through a
chromatographic column of resin layers;
thirdly, eluting the sweet glycosides from the resin using
a water soluble organic solvent to recover the liquid solution
of mixed sweet glycosides with some impurities removed;
fourthly, crystallizing the liquid solution of mixed sweet
glycosides to obtain a crystallized solid containing a higher
concentration of a selected sweet glycoside and a waste liquor
containing other sweet glycosides;
fifthly, dissolving the crystallized solid containing a
higher concentration of the selected sweet glycoside using a
water soluble organic solvent to obtain a sweet liquor of the
selected sweet glycoside;
sixthly, crystallizing the sweet liquor of the selected
sweet glycoside to obtain a second crystallized solid
containing an even higher concentration of the selected sweet
glycoside and a second waste liquor containing other sweet
glycosides; and
seventhly, repeating steps five and six until a final
crystallized solid of desired purity of the selected sweet
glycoside is obtained.

Description

21 85496
TITLE OF THE INVENTION:

method of extracting selected sweet glycosides from the
stevia rebaudiana plant




NAMES OF INVENTORS:

John Donald Payzant
James Kenneth Laidler
Robert Maurice Ippolito

FIELD OF THE INVENTION
The present invention relates to a method of extracting
selected sweet glycosides from the stevia rebaudiana plant.

R~CRGROUND OF THE INVENTION

Japanese Patent 63173531 which issued in 1988 to Nakazato
describes a method of extracting sweet glycosides from the
stevia rebaudiana plant. This method includes the following
steps. Firstly, extracting a liquid solution of sweet
glycosides from the stevia rebaudiana plant. Secondly, passing
the liquid solution of sweet glycosides through a non-polar
porous resin, such as amberlite XAD-2 and eluting with a water
soluble organic solvent, preferably methanol. Thirdly,
concentrating and drying the eluted solution to give a powdery
material.

Subsequent patents, such as Korean Patent 9007421, have
added to or varied the Nakazato process in an attempt to
improve the purity and yield. Korean Patent 9007421, which
issued in 1990 to Pacific Chemical Company, passes the eluted
solution through a column which is packed with positive ion-


2 2 1 85496
exchange resin (preferably Diaion SKlB) and negative ion-
exchange resin (Amberite IRA 904).

Of the sweet glycosides extracted from the stevia
rebaudiana plant, rebaudioside A is recognized as having the
most desirable sensory properties. The problem with the above
described methods is that the resulting materials contain a
mixture of all of the sweet glycosides.

SU~ARY OF THE INVENTION

What is required is a method of extracting selected sweet
glycosides from the stevia rebaudiana plant.
According to the present invention there is provided a
method of extracting selected sweet glycosides from the stevia
rebaudiana plant. Firstly, extracting a liquid solution of
mixed sweet glycosides from the stevia rebaudiana plant using
a water soluble organic solvent. Secondly, crystallizing the
liquid solution of sweet glycosides to obtain a crystallized
solid containing a higher concentration of a selected sweet
glycoside and a waste liquor contAin;ng other sweet glycosides.

Unlike prior art methods which produce a powdery mixture
of sweet glycosides, the above described method results in a
crystallized solid contAining a higher concentration of the
selected sweet glycoside. The selected sweet glycoside will
normally, but not necessarily be rebaudioside A.
Although beneficial results may be obtained through the
method, as described above, the higher the purity of
rebaudioside A the better. It is, therefore, preferred that
the method include further steps. Thirdly, dissolving the
crystallized solid contAining a higher concentration of the
selected sweet glycoside using a water soluble organic solvent
to obtain a sweet liquor of the selected sweet glycoside.

3 2~85496
Fourthly, crystallizing the sweet liquor of the selected sweet
glycoside to obtain a second crystallized solid cont~ining an
even higher concentration of the selected sweet glycoside and
a second waste liquor contAining other sweet glycosides. These
steps are, preferably, repeated over and over until a final
crystallized solid of desired purity of the selected sweet
glycoside is obtained.

Although beneficial results may be obtained through the
use of the method described, there are impurities present in
the sweet glycosides that adversely affect both the purity and
the yield obtained. Even more beneficial results may,
therefore, be obtained when an intermediate step is added of
removing impurities in the liquid solution of sweet glycosides
by column chromatography prior to crystallization. These
impurities are primarily polysaccharides.


DETATT-~n DESCRIPTION OF THE EA~rr;KK~ EMBODIMENT
The preferred method of extracting sweet glycosides from
the stevia rebaudiana plant includes the following steps.

Firstly, extracting a liquid solution of sweet glycosides
from the stevia rebaudiana plant. There are a variety of
suitable extraction methods described in the technical
literature. Beneficial results have been obtained through a
hot water extraction method.

Secondly, passing the liquid solution of sweet glycosides
through a chromatographic column of resin layers. There are
a variety of suitable resins. It is preferred, however, that
the resin be based upon acrylic ester chemistry. An example
of such a resin is the Amberlite XAD-7 resin commercially
available through Rhom and Haas. An alternative resin is
reverse phase C18 bonded silica. During column chromatography
the sweet glycosides tend to be absorbed by the resin, while

4 21 85496
polysaccharide impurities were not absorbed.

Thirdly, eluting the sweet glycosides from the resin using
a water soluble organic solvent to recover the liquid solution
of mixed sweet glycosides with some impurities removed. The
preferred form of water soluble organic solvent is a methanol
solution.

Fourthly, crystallizing the liquid solution of sweet
glycosides to obtain a crystallized solid cont~in;ng a higher
concentration of a selected sweet glycoside and a waste liquor
cont~;ning other sweet glycosides. The selected sweet
glycoside will normally be rebaudioside A. The waste liquor
may either be disposed of or may be subject to further
crystallization to remove another of the sweet glycosides, such
as stevioside.

Fifthly, dissolving the crystallized solid cont~ining a
higher concentration of the selected sweet glycoside using a
water soluble organic solvent to obtain a sweet liquor of the
selected sweet glycoside. The preferred form of water soluble
organic solvent is a methanol solution.

Sixthly, crystallizing the sweet liquor of the selected
sweet glycoside to obtain a second crystallized solid
cont~ining an even higher concentration of the selected sweet
glycoside and a second waste liquor cont~;n;ng other sweet
glycosides.

Seventhly, repeating steps five and six until a final
crystallized solid of desired purity of the selected sweet
glycoside is obtained.

It will be apparent to one skilled in the art that
modifications may be made to the illustrated embodiment without
departing from the spirit and scope of the invention as
hereinafter defined in the Claims.