.ALPHA.-Anomer-Selective Glucosylation of (+)-Catechin by the Crude Enzyme, Showing Glucosyl Transfer Activity, of Xanthomonas campestris WU-9701.

Abstract

Alpha-anomer-selective glucosylation of (+)-catechin was carried out using the crude enzyme, showing alpha-glucose transferring activity, of Xanthomonas campestris WU-9701 with maltose as a glucosyl donor. When 60 mg of (+)-catechin and 50 mg of the enzyme (5.25 units as maltose hydrolysing activity) were incubated in 10 ml of 10 mM citrate-Na2HPO4 buffer (pH 6.5) containing 1.2 M maltose at 45 degrees C, only one (+)-catechin glucoside was selectively obtained as a product. The (+)-catechin glucoside was identified as (+)-catechin 3'-O-alpha-D-glucopyranoside (alpha-C-G) by 13C-NMR, (1)H-NMR and two-dimensional HMBC analysis. The reaction at 45 degrees C for 36 h under the optimum conditions gave 12 mM alpha-C-G, 5.4 mg/ml in the reaction mixture, and the maximum molar conversion yield based on the amount of (+)-catechin supplied reached 57.1%. At 20 degrees C, the solubility in pure water of alpha-C-G, of 450 mg/ml, was approximately 100 fold higher than that of (+)-catechin, of 4.6 mg/ml. Since alpha-C-G has no bitter taste and a slight sweet taste compared with (+)-catechin which has a very bitter taste, alpha-C-G may be a desirable additive for foods, particularly sweet foods.