Influence of Simulated Gastrointestinal Digestion on Phenolic Composition, Bioaccessibility, and Antioxidant Properties of Commercial Wild Rice

Wild rice (Zizania palustris L.; WR) is a nutrient-dense whole grain, naturally rich in phenolic acids with established antioxidant and health-promoting properties. This study investigated the effect of cooking and in vitro gastrointestinal digestion on the phenolic composition, bioaccessibility, and antioxidant capacity of commercial WR samples. Free phenolics predominated over bound forms in both raw and cooked samples, indicating that WR is a rich source of extractable phenolics. Cooking reduced total phenolics by 17–23% across WR varieties. Among individual compounds, p-hydroxybenzoic acid (up to 58.3%) and caffeic acid (up to 56.5%) exhibited the greatest bioaccessibility indices, while ferulic acid remained largely insoluble. In vitro gastrointestinal digestion facilitated the release of some bound phenolics, particularly during the intestinal phase, resulting in a total phenolic content (TPC) bioaccessibility of up to 22.61%. However, antioxidant activities, as measured by DPPH and ABTS assays, declined compared to cooked samples (5.53% and 9.34%, respectively). These findings reveal dynamic changes in phenolic composition and bioaccessibility during cooking and digestion, with the intestinal phase being pivotal for releasing certain bound phenolics. This underscores WR’s promise as a functional food source for phenolics, while highlighting the importance of evaluating food bioactives under physiologically relevant conditions.