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

摘要

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 12Leuconostocand 5Weissellastrains 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 ofL. citreumDSM 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-alpha-d-glucoside. OnlyL. kimchiB-65337 produced a second catechin monoglucoside. Four out of six glucansucrases glucosylated esculetin and all enzymes were active on haematoxylin. Glucansucrases ofL. citreumDSM 5577,L. kimchiB-65337 andW. beninensisDSM 22752 were the best suited biocatalysts with conversions of >30 for esculetin and >60 for haematoxylin.W. beninensisDSM 22752 glucansucrase produced 89 haematoxylin glucosides without process optimization.L. kimchiB-65337 andW. beninensisDSM 22752 synthesized >40 diglucosides with the bifunctional haematoxylin. NMR analysis of the purified esculetin products confirmed formation of the 6-O-alpha-d- and 7-O-alpha-d-glucosides. Also two haematoxylin monoglucosides were identified as the 9-O-alpha-d- and 3-O-alpha-d-glucosides.