Synthesis of epicatechin glucosides by a β-cyclodextrin glycosyltransferase

Abstract

Enzymatic synthesis of (−)-epicatechin (EC) glucosides was performed through the transglucosylation reaction catalyzed by the cyclodextrin glycosyltransferase (CGTase) from Paenibacillus sp. RB01. The enzyme showed the same product specificity for the three donor substrates, starch, β-cyclodextrin and maltoheptaose (G7). Using β-cyclodextrin as the glucosyl donor, several EC glucoside products were obtained at an overall minimal yield of 18.1%. The structures of the four main products were elucidated by MS and NMR techniques as (−)-EC-3′-O-α-d-glucopyranoside (EC3A), (−)-EC-3′-O-α-d-diglucopyranoside (EC3B), (−)-EC-3′-O-α-d-triglucopyranoside (EC3C) and (−)-EC-4′-O-α-d-glucopyranoside (EC4A). Of these, EC3A was the major product while EC4A, unique for this CGTase, was formed in the lowest amount. The water solubility and stability against UV irradiation of EC3A were significantly higher than that of EC. Although the antioxidant activity was 1.5-fold lower, the advantage of the enhanced solubility and stability makes the EC3A glucoside more beneficial as food ingredient than its parent EC.