Post-digestive cellular activity and in vitro colonic fermentation of tannat grape pomace-enriched biscuits

Abstract

Valorization of grape pomace as an upcycled food ingredient offers a sustainable strategy for incorporating polyphenols and nondigestible components into food formulations. However, limited information is available on the post-digestive cellular activity and colonic fermentability of grape pomace when incorporated into baked products. This study evaluated Tannat grape pomace (TGP)-enriched biscuits using in vitro gastrointestinal digestion, Caco-2 cell assays, and in vitro colonic fermentation. After digestion, the bioaccessible fraction (BF) and colonic fraction (CF) of the TGP-enriched biscuit reduced intracellular reactive oxygen species (ROS) formation by 93.45% and 89.34%, respectively, relative to cells treated with the oxidative stress inducer 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH). Four phenolic compounds were detected in Caco-2 cell extracts after exposure to the TGP-enriched biscuit CF; malvidin-3-O-glucoside and malvidin-3-O-(6′-p-coumaroyl)glucoside were estimated at 16.51 and 32.94 µg g⁻¹ CF, respectively. The CFs were subsequently fermented in vitro, and short-chain fatty acids (SCFAs) and lactate concentrations were monitored at 0, 24, 48, and 72 h. At 48 h, acetate and propionate concentrations in the TGP-enriched biscuit CF were 21.50 ± 1.28 and 24.39 ± 1.52 mM, respectively, and were significantly (p < 0.05) higher than the corresponding concentrations in the control biscuit CF (11.07 ± 0.13 and 11.41 ± 0.46 mM, respectively). At this time point, lactate was not detected in the TGP-enriched biscuit CF, whereas its concentration in the control biscuit CF was 18.47 ± 0.94 mM. Denaturing gradient gel electrophoresis (DGGE) showed differences in microbial community fingerprints after 48 h. Overall, TGP-enriched biscuits showed post-digestive cellular activity and fermentability, highlighting the potential of TGP as an upcycled ingredient for functional food formulations and supporting further in vivo evaluation.