Glycosylation of genistin into soluble inclusion complex form of cyclic glucans by enzymatic modification.

The enzymatic modification of genistin to enhance its water solubility was studied using two glycosyltransferases, cyclodextrin glucanotransferase from alkalophilic Bacillus sp. I-5 and 4-alpha-glucanotransferase from Thermus scotoductus. Two different catalytic reactions, the transglycosylation and cyclization activities, were observed when the reaction was performed with soluble starch as a donor and genistin as an acceptor. The reaction products were isolated and identified as [Glc(alpha1-4)](1-22)-Glc(beta1-7)-genisteins and cycloamylose with DP 8-12 by HPLC and MALDI-TOF MS. A beta-amylase treatment revealed inclusion complexes composed of Glc(alpha1-4)-Glc(beta1-7)-genistein/Glc(alpha1-4)-Glc(alpha1-4)-Glc(beta1-7)-genistein and cycloamylose with DP 8-12. The results indicated that the cycloamylose formed by the cyclization reaction of the enzyme included Glc(alpha1-4)-Glc(beta1-7)-genistein/Glc(alpha1-4)-Glc(alpha1-4)-Glc(beta1-7)-genistein. The presence of cycloamylopectin, in which the Glc(alpha1-4)-Glc(beta1-7)-genistein/Glc(alpha1-4)-Glc(alpha1-4)-Glc(beta1-7)-genistein was enclosed, was also observed with HPLC, HPSEC-MALLS, and MALDI-TOF MS analyses. The solubility of genistin was highly improved, and the solution containing glycosylated genistin and the inclusion complex demonstrated excellent properties of transparency and stability during storage at 4 degrees C.