A comparison of the in vitro biotransformation of (-)-epicatechin and procyanidin B2 by human faecal microbiota

The catabolism by human faecal microbiota of (-)-epicatechin (1) (2, 3-cis stereochemistry) and its dimer pure procyanidin B2 (2), has been compared using a static in vitro culture model. The catabolites were characterised by LC-MSⁿ, UV absorption and relative retention time, and quantified relative to standards. No more than ~10% of procyanidin B2 (2) was converted to epicatechin (1) by scission of the interflavan bond. Five phenolic acid catabolites (M_r<290) were unique to 2, and ten phenolic acid catabolites (M_r<290) were common to both substrates. The dominant catabolites (≥24 h incubation) were 5-(3′-hydroxy phenyl) valeric acid (9), 3-(3′-hydroxyphenyl) propionic acid (10) and phenyl acetic acid (12) (maximum yields 27.4±4.2, 38.2±4.2, 22.7±2.9%, respectively, from 1 and 9.4±1.2, 52.8±2.1, 28.8±1.6%, respectively, from 2). Substrate 2 was degraded twice as rapidly as 1. Evidence is presented for the production of previously unreported catabolites of 2 that retain the flavanol A-ring and the C4 → C8 interflavan bond. It was confirmed that catabolism favoured removal of the 4′-hydroxyl rather than the 3′-hydroxyl group and that both β-oxidation and α-oxidation occurred.