alpha-Anomer-selective glucosylation of (+)-catechin by the crude enzyme, showing glucosyl transfer activity, of Xanthomonas campestris WU-9701

alpha -Anomer-selective glucosylation of(+)-catechin was carried out using the crude enzyme, showing a-glucose transferring activity, of Xanthomonas c ampestris WU-9701 with maltose as a glucosyl donor. When 60 mg of (+)-catec hin and 50 mg of the enzyme (5.25 units as maltose hydrolysing activity) we re incubated in 10 mi of 10 mM citrate-Na2HPO4 buffer (pH 6.5) containing 1 .2 M maltose at 45 degreesC, only one (+)-catechin glucoside was selectivel y obtained as a product. The (+)-catechin glucoside was identified as (+)-c atechin 3'-O-alpha -D-glucopyranoside (alpha -C-G) by C-13-NMR, H-1-NMR and two-dimensional HMBC analysis. The reaction at 45 degreesC for 36 h under the optimum conditions gave 12 mM alpha -C-G, 5.4 mg/ml in the reaction mix ture, and the maximum molar conversion yield based on the amount of (+)-cat echin supplied reached 57.1%. At 20 degreesC, 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 slig ht sweet taste compared with (+)-catechin which has a very bitter taste, al pha -C-G may be a desirable additive for foods, particularly sweet foods.