Glucansucrases From Lactic Acid Bacteria As Biocatalysts For Multi-Ring Catechol Glucosylation

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.