Study on Improved Utilization of Sweet Natural Glycosides by Enzymic Transglycosylation

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In order to improve intensity and quality of sweetness, enzymic transglucosylation of sweet natural glycosides, stevioside(S) and rubusoside(R) has been investigated.The complete separation and identification of alpha-1,4-glucosylated products from S and R with soluble starch and cycloddxtringlucosyltransferase (CGTase) were achieved.The beta-glucosyl ester group at 19-carboxylic acid of S and R was chemically replaced by a beta-galactosyl group as a blocker against the glucosylation with CGTase. Both the galactosyl esters were regioselectively glucosylated on the 13-glycosyl moiety with CGTase.The evaluation of sweetness of all of the above glucosylated products revealed the following structure-sweetness relationship of glycosides of this series. Remarkable improvement in both the intensity and quality of sweetness was observed for the products which have three or four glucosyl groups at the 13-position. It was noted that the products having more glucosyl groups at the 13-position sho … More wed less sweetness. Transglucosylation at the 19-position also resulted in the decrease of sweetness.The regioselective control of the enzymic transglycosylation of S has been studied under the various conditions. It was found that in the presence of tubeimoside-I which has the potent inclusion property, the glucosylation of S at the 19-position was suppressed, leading to the decrease of the production of the worse sweeteners.Blocking of the 4-hydroxyl group of the 19-COO-beta-glucosyl group of R against glucosylation with CGTase has been investigated extensively by galactosylation with a variety of alpha- and beta-galactosidases. It was disclosed that beta-galactosylation of R with lactose and beta-galactosidase produced by Bacillus circulans effectively afforded the 19--COO-beta-galactosyl-(l--4)-beta-glucoside. Transgiucosylation of this compound with CGTase followed by de-galactosylation with beta-galactosidase yielded the better sweeteners which were mono-, di- or tri-glucosylated exclusively at 13-position.Solubilization of alpha-tochopherol in water was observed for sweet Stevia glycosides, S and rebaudioside-A. Less