Glucansucrases from lactic acid bacteria as biocatalysts for multi-ring catechol glucosylation

Abstract

Catechins are the major group of bioactive flavanols in green tea and cacao. 17 glucansucrase-active strains were identified from a set of 41 lactic acid bacteria, which were able to glucosylate (+)-catechin in a non-natural acceptor reaction. In total cell free extracts of 12 Leuconostoc and 5 Weissella strains were active on catechin and also 8 cell fractions exhibited catechin glucosylation activity. Six enzymes were selected for further evaluation and enriched up to 37 fold in yields of at least 40%. Glucansucrase of L. citreum DSM 5577 was the most efficient biocatalyst for (+)-catechin transformation with conversions of >40% after 24 h. NMR analysis of the major reaction product confirmed the (+)-catechin-4′-O-α-d-glucoside. Only L. kimchi B-65337 produced a second catechin monoglucoside. Four out of six glucansucrases glucosylated esculetin and all enzymes were active on haematoxylin. Glucansucrases of L. citreum DSM 5577, L. kimchi B-65337 and W. beninensis DSM 22752 were the best suited biocatalysts with conversions of >30% for esculetin and >60% for haematoxylin. W. beninensis DSM 22752 glucansucrase produced 89% haematoxylin glucosides without process optimization. L. kimchi B-65337 and W. beninensis DSM 22752 synthesized >40% diglucosides with the bifunctional haematoxylin. NMR analysis of the purified esculetin products confirmed formation of the 6-O-α-d- and 7-O-α-d-glucosides. Also two haematoxylin monoglucosides were identified as the 9-O-α-d- and 3-O-α-d-glucosides.