Antibacterial and enzyme inhibitory activities of flavan-3-ol monomers and procyanidin-rich grape seed fractions

This study aimed to determine structure-function relationships of monomeric and oligomeric flavan-3-ols (procyanidins) with respect to their antimicrobial activity and their inhibition of digestive enzymes. Monomeric flacan-3-ols were purchased as reference compounds; oligomeric procyanidins were extracted from grape seeds, separated by high-performance counter-current chromatography and characterized by LC-MS/MS. The antimicrobial activity against a broad range of intestinal microorganisms increased in the order catechin = epicatechin > epigallocatechin and oligomeric procyanidins > epigallocatechin gallate. Facultative anaerobes were highly resistant while strict anaerobes including Allobaculum sp. and Ruminococcus gnavus were 10 - 100 times more sensitive. The inhibition of digestive enzymes from the rat small intestine increased in the order catechin < epicatechin and oligomeric procyanidins < epigallocatechin < epigallocatechin gallate. Trimeric and polymeric procyanidins were more inhibitory than dimeric procyanidins. Both the antimicrobial and enzyme-inhibitory activities of procyanidins and flavan-3-ols likely relate to their microbiome-modulating and health beneficial properties.