High-purity steviol glycosides

Abstract

Methods of preparing highly purified steviol glycosides, particularly rebaudiosides A, D and X are described. The method includes expression of UDP-glucosyltransferases from Stevia rebaudiana Bertoni, which are capable converting certain steviol glycosides to rebaudiosides A, D and X. The highly purified rebaudiosides A, D and X, are useful as non-caloric sweetener in edible and chewable compositions such as any beverages, confectioneries, bakery products, cookies, and chewing gums.

1 .- 26 . (canceled) 
     
     
         27 . A method for adding at least one glucose unit to a steviol glycoside substrate comprising rebaudioside E to provide a target steviol glycoside, comprising contacting the steviol glycoside substrate with a biocatalyst protein enzyme comprising UDP-glucosyltransferase, wherein the target steviol glycoside is Rebaudioside X. 
     
     
         28 . The method of  claim 27 , wherein the biocatalyst protein enzyme is a recombinant protein. 
     
     
         29 . The method of  claim 27 , further comprising the step of purifying the Rebaudioside X to a purity of greater than about 80% by weight. 
     
     
         30 . The method of  claim 27 , further comprising the step of purifying the Rebaudioside X to a purity of greater than about 90% by weight. 
     
     
         31 . The method of  claim 27 , further comprising the step of purifying the Rebaudioside X to a purity of greater than about 95% by weight. 
     
     
         32 . The method of  claim 27 , wherein the UDP-glucosyltransferase is expressed in a host microorganism. 
     
     
         33 . The method of  claim 32 , wherein the host microorganism is selected from the group consisting of:  Escherichia coli, Saccharomyces species, Aspergillus  species, and  Pischia  species.