Prior Exposure of Cecal Microflora to Grape Pomaces Does Not Inhibit in Vitro Fermentation of Pectin

Abstract

Grape pomace is mainly composed of dietary fiber (DF) and polyphenols (PP), components of the undigestible residue and substrates for colonic fermentation. Male Wistar rats were fed fiber-free diets supplemented with 5% cellulose or 10% red grape peels (RGP), white grape peels (WGP), or white grape seeds (WGS) as source of DF for 6 weeks, and rat cecal contents from fasted rats were used as inoculum to in vitro ferment apple pectin. Short-chain fatty acid (SCFA) production, pH, and pressure were measured as indications of fermentative capacity at different times. SCFA production at 24 h, expressed as micromoles per milligram of dry substrate, was significantly higher in RGP (9.7) and WGS (9.6) groups than in the control group (8.8). Fermentative capacity of cecal contents from WGP-fed rats did not differ from that of the control group (8.5 μmol/mg of dry substrate). The presence of the three test materials in the diets did not modify the fermentation rate. SCFA production was significantly correlated with pH values (r = −0.969) and gas production (r = 0.960). In conclusion, DF rich in PP did not inhibit colonic fermentation; furthermore, some materials enhanced the process. Keywords: Dietary fiber; polyphenols; in vitro fermentation; rats