Metabolism of Turkish black tea phenolics by human gut microbiota

Human gut microbiota has diverse microbial community with diverse and intense metabolic activity on non-digested dietary substances, easing the absorption. Phenolics, kind of dietary compounds with exceptional nutritive and health related value, are expose to colonic metabolism and/or release their local or systemic effects on human body. In this study, gut microbiota dependent metabolism of Turkish black tea phenolics were investigated in a pH-controlled fermentor system using fecal inocula from a Turkish healthy male. Before being set up, brewing conditions and inoculation amount of black tea extract were optimized and initially performed in static cultures. Cultures were grown in synthetic medium at 37°C under flowing nitrogen with (R1) or without (R2) addition of black tea extract (3125 mg/L) for 48 h. The activities of microbiota on phenolic metabolism were monitored by degradation of catechins using HPLC-PDA and production of their metabolites using GC-MS. For microbial profile, plate counting and FISH analysis were performed. EC, EGCG, ECG and theaflavins were significantly and completely metabolized during 24 h period relative to control (R3) (p<0.05), leading to generation of pyrocatechol, pyrogallol, 4-hydroxyphenylacetic acid, 3-(3-hydroxyphenyl) propionic acid with a significant correlation (p<0.05) and trace amount of GA were observed at the end of incubation, yielding the pyrogallol and pyrocatechol (p<0.05). Moreover, the uncontrolled pH in static cultures led to faster degradation of phenolics. The bacterial plate counting analysis revealed that no significant differences were observed in black tea inoculated cultures compared to control (p>0.05). In FISH analysis, the background noise obstructed the quantification of bacteria in the images, so the analysis should be repeated to obtain reproducible accuracy.