Bioaccessibility and antioxidant activity of phenolic compounds from roasted date seed during in vitro digestion

Date seed, a by-product of date processing, is a rich source of phenolic compounds. However, the impact of roasting on digestibility, bioavailability and functionality remains unclear. This study evaluated roasting effects (light = 180 °C, medium = 200 °C, dark = 220 °C; 15 min) on phenolic composition, antioxidant activity, and bioaccessibility of seed from three date cultivars (Khadrawy, Medjool, Barhee) using in vitro digestion model. Total phenolic content and antioxidant capacity increased, peaking in the intestinal phase. In contrast, condensed tannins became undetectable after this stage. Gallic acid had the greatest bioaccessibility, exceeding 200% in the oral phase (e.g., 328.5% in medium-roasted Medjool) before declining to 85.9-188.0% in the intestinal phase. Protocatechuic acid also increased, reaching 372.9% in light-roasted Barhee. Light roasting enhanced release of free phenolics, medium roasting promoted bound phenolic release, and dark roasting reduced stability. These findings demonstrated that moderate roasting enhanced in vitro phenolic retention and bioaccessibility.