High-purity steviol glycosides

Abstract

Methods of preparing highly purified steviol glycosides, particularly Rebaudioside D, are described. The methods include purification from the extraction stage of the Stevia rebaudiana Bertoni plant, purification of steviol glycoside mixtures, Rebaudioside D and Rebaudioside A from a commercial Stevia extract, and purification of Rebaudioside D from remaining solutions obtained after isolation and purification of Rebaudioside A and a high purity mixture of steviol glycosides. The methods are useful for producing high purity Rebaudioside D, Rebaudioside A, and steviol glycoside mixtures. The high purity steviol glycosides are useful as non-caloric sweeteners in edible and chewable compositions such as any beverages, confectioneries, bakery products, cookies, and chewing gums.

We claim: 
     
         1 . A method for purifying steviol glycosides, comprising the steps of:
 a. providing a solution of steviol glycosides;   b. passing the solution of steviol glycosides through a multi-column system including a plurality of columns packed with an adsorbent resin, to obtain at least one column having adsorbed steviol glycosides;   c. removing impurities from the multi-column system; and   d. eluting the adsorbed steviol glycosides from the at least one column, to obtain an eluted solution comprising steviol glycosides.   
     
     
         2 . The method of  claim 1 , wherein impurities are removed by eluting the multi-column system with a washing solution. 
     
     
         3 . The method of  claim 2 , wherein the washing solution comprises an aqueous alcohol solution having a water to alcohol ratio ranging from about 99.9:0.1 to about 60:40. 
     
     
         4 . The method of  claim 1 , wherein the adsorbed steviol glycosides are eluted with an aqueous alcohol solution having a water to alcohol ratio ranging from about 60:40 to about 0.1:99.9. 
     
     
         5 . The method of  claim 1 , wherein at least two columns of the plurality of columns are connected in series. 
     
     
         6 . The method of  claim 1 , wherein at least two columns of the plurality of columns are connected in parallel. 
     
     
         7 . The method of  claim 1 , wherein a ratio of a volume of a first column of the plurality of columns to a volume of a second column of the plurality of columns is in the range of about 1:1 to about 1:10. 
     
     
         8 . The method of  claim 1 , wherein a ratio of a volume of a last column of the plurality of columns to a volume of a penultimate column of the plurality of columns is in the range of about 3:1 to about 1:10. 
     
     
         9 . The method of  claim 1 , wherein the adsorbent resin comprises a macroporous polymeric resin capable of adsorbing steviol glycosides. 
     
     
         10 . The method of  claim 1 , wherein the solution of steviol glycosides is obtained by dissolving a steviol glycoside mixture in a solvent, and further comprising the step of drying the eluted solution comprising steviol glycosides to obtain a purified steviol glycoside mixture. 
     
     
         11 . The method of  claim 10 , wherein the purified steviol glycoside mixture has a purity level of at least about 95% (w/w) on a dry basis. 
     
     
         12 . A purified steviol glycoside mixture made by the method of  claim 10 . 
     
     
         13 . A product comprising the purified steviol glycoside mixture of  claim 12 , wherein the product is selected from the group consisting of a food, a beverage, a pharmaceutical composition, a tobacco product, a nutraceutical composition, an oral hygiene composition, and a cosmetic composition. 
     
     
         14 . The method of  claim 1 , wherein the solution of steviol glycosides is obtained by dissolving a steviol glycoside mixture in a solvent, and wherein prior to eluting adsorbed steviol glycosides, high Rebaudioside D fractions are eluted with an aqueous alcohol solution. 
     
     
         15 . The method of  claim 14 , further comprising the steps of:
 a. mixing the high Rebaudioside D fractions with a first aqueous alcohol solution to obtain a Rebaudioside D solution;   b. inducing crystallization to obtain first crystals of Rebaudioside D;   c. separating the first crystals of Rebaudioside D from the Rebaudioside D solution, said first crystals having a purity level greater than about 60% (w/w) on a dry basis;   d. suspending the first crystals of Rebaudioside D in a second aqueous alcohol solution to obtain second crystals of Rebaudioside D and a third aqueous alcohol solution; and   e. separating the second crystals of Rebaudioside D from the third aqueous alcohol solution, said second crystals having a purity level greater than about 95% (w/w) on a dry basis.   
     
     
         16 . A purified Rebaudioside D made by the method of  claim 15 . 
     
     
         17 . A product comprising the purified Rebaudioside D of  claim 16 , wherein the product is selected from the group consisting of a food, a beverage, a pharmaceutical composition, a tobacco product, a nutraceutical composition, an oral hygiene composition, and a cosmetic composition. 
     
     
         18 . The method of  claim 1 , wherein the solution of steviol glycosides is prepared by
 a. providing a biomass of a  Stevia rebaudiana  Bertoni plant;   b. producing a crude extract by contacting the biomass with water;   c. separating insoluble material from the crude extract to obtain a filtrate containing steviol glycosides; and   d. treating the filtrate to remove high molecular weight compounds and insoluble particles to obtain the solution of steviol glycosides.   
     
     
         19 . The method of  claim 18 , further comprising the steps of:
 a. treating the eluted solution to obtain a decolorized solution;   b. evaporating the solvent from the decolorized solution to obtain a first adsorption solution;   c. passing the first adsorption solution through a column with a macroporous adsorbent to obtain a second adsorption solution;   d. deionizing and concentrating the second adsorption solution; and   e. drying the deionized and concentrated second adsorption solution to obtain a purified steviol glycoside mixture with at least about 95% by weight total steviol glycosides.   
     
     
         20 . A purified steviol glycoside mixture made by the method of  claim 19 . 
     
     
         21 . A product comprising the purified steviol glycoside mixture of  claim 20 , wherein the product is selected from the group consisting of a food, a beverage, a pharmaceutical composition, a tobacco product, a nutraceutical composition, an oral hygiene composition, and a cosmetic composition. 
     
     
         22 . The method of  claim 18 , further comprising eluting high Rebaudioside D fractions from the multi-column system to obtain an eluted Rebaudioside D solution. 
     
     
         23 . The method of  claim 22 , further comprising the steps of:
 a. treating the eluted Rebaudioside D solution to obtain a decolorized solution;   b. evaporating solvent from the decolorized solution to obtain a high Rebaudioside D content mixture;   c. combining the high Rebaudioside D content mixture with solvent to form a Rebaudioside D solution or suspension; and   d. crystallizing Rebaudioside D from the Rebaudioside D solution or suspension to obtain Rebaudioside D crystals.   
     
     
         24 . The method of  claim 23 , further comprising the steps of:
 a. separating the Rebaudioside D crystals from the Rebaudioside D solution or suspension;   b. combining the Rebaudioside D crystals with solvent to form a purified Rebaudioside D solution or suspension;   c. crystallizing purified Rebaudioside D from the purified Rebaudioside D solution or suspension to obtain purified Rebaudioside D crystals;   d. separating the purified Rebaudioside D crystals from the purified Rebaudioside D solution or suspension; and   e. drying the purified Rebaudioside D crystals.   
     
     
         25 . The method of  claim 24 , wherein the purified Rebaudioside D crystals have a purity level greater than about 95% (w/w) on a dry basis. 
     
     
         26 . A purified Rebaudioside D made by the method of  claim 25 . 
     
     
         27 . A product comprising the purified Rebaudioside D of  claim 26 , wherein the product is selected from the group consisting of a food, a beverage, a pharmaceutical composition, a tobacco product, a nutraceutical composition, an oral hygiene composition, and a cosmetic composition.