Modification of ascorbic acid using transglycosylation activity of Bacillus stearothermophilus maltogenic amylase to enhance its oxidative stability

Ascorbic acid (1), a natural antioxidant, was modified by employing transglycosylation activity of Bacillus stearothermophilus maltogenic amylase with maltotriose and acarbose as donor molecules to enhance its oxidative stability. The transglycosylation reaction with maltotriose as donor created mono- and di-glycosyl transfer products with an α-(1,6)-glycosidic linkage. In addition, two acarviosine-glucosyl transfer products were generated when transglycosylation was performed with acarbose as a donor. All transfer products were observed by TLC and HPLC, and purified by Q-sepharose anion exchange and Biogel P-2 gel permeation chromatographies. LC/MS and ¹³C NMR analyses revealed that the structures of the transfer products were 6-O-α-D-glucosyl- (2) and 6-O-α-D-maltosyl-ascorbic acids (3) in the reaction of maltotriose, and 6-O-α-acarviosine-D-glucosyl- (4) and 2-O-α-acarviosine- D-glucosyl ascorbic acids (5) in the reaction of acarbose. The stability of the transglycosylated ascorbic acid derivatives was greatly enhanced against oxidation by Cu²⁺ ion and ascorbate oxidase. Among them, compound 3 proved to be the most stable against in vitro oxidation. The antioxidant effects of glycosyl-derivatives of ascorbic acid on the lipid oxidation in cooked chicken breast meat patties indicated that they had antioxidant activities similar to that of ascorbic acid. It is suggested that the transglycosylated ascorbic acids can possibly be applied as effective antioxidants with improved stability in food, cosmetic, and other applications.