Assessing the effect of gastrointestinal conditions and solubility on the bioaccessibility of polyphenolic compounds from a white grape marc extract

This study investigates the bioaccessibility of phenolic compounds from a Vitis vinifera marc extract using an in vitro gastrointestinal model. Both undiluted and five-fold diluted extracts were digested to assess how solubility and gastrointestinal conditions impact polyphenol bioaccessibility. The extract was obtained using the environmentally friendly Medium Scale Ambient Temperature (MSAT) system. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis revealed that gastric digestion significantly increased polyphenolic content, particularly catechin, epicatechin, and procyanidins. Diluted extracts showed 30 % higher polyphenolic content and a 200 % increase in gallic acid compared to undigested samples. However, bioaccessibility decreased during intestinal digestion. Interaction tests with bile salts revealed 50 % polyphenol insolubility, suggesting that some compounds may remain in the residual fraction and serve as substrates for colonic microbiota fermentation. These findings emphasize the crucial role of gastrointestinal digestion in polyphenol bioaccessibility and highlight white grape marc extract as a potential source of bioactives for microbiota modulation and functional nutrition.