Matrix characteristics modulate black rice phenolic compounds bioaccessibility and antioxidant activity during simulated gastrointestinal digestion

Black rice (Oryza sativa L.) is a valuable source of bioactive phenolic compounds. This study aimed to explore the impact of the rice matrix on the recovery and bioaccessibility of total phenolic content (TPC), total anthocyanin content (TAC), phenolic composition, and total antioxidant activity (TAA) quantified as 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity, 2,2-azinobis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS) radical cation, and ferric reducing activity power (FRAP) during simulated gastrointestinal digestion, in addition to physicochemical characterization of the samples. Freshly cooked black rice (CBR) and black rice phenolic extract (BRE) were subjected to three-phase simulated gastrointestinal digestion. The results showed that the CBR showed a lower recovery index for TPC, TAC, and TAA than that of the BRE during oral and gastric digestion. However, intestinal digestion of CBR increased the TPC and TAC recovery indices compared with the BRE matrix. Digestion of the CBR matrix resulted in a marked improvement (p < 0.05) in the bioaccessibility of monomeric anthocyanins and FRAP activity while maintaining comparable levels (p > 0.05) of TPC, ABTS, and gallic acid to the BRE matrix. Cyanidin-3-glucoside decomposition was evident during the intestinal digestion of both samples, followed by a notable surge in gallic acid and protocatechuic acid. Isolated starch (BRS) demonstrated superior starch digestibility during oral and intestinal digestion compared with CBR. The samples displayed distinct matrix characteristics, which were confirmed by the DSC, FTIR, and XRD patterns. These findings highlight the significance of the digestion matrix in determining the bioavailability and antioxidant capacity of rice-derived phenolic compounds.