Bioactive Phenolic Compounds from Apples during Simulated In Vitro Gastrointestinal Digestion: Kinetics of Their Release

Bioactive phenolic compounds in their natural form show beneficial effects on the gastrointestinal system. The kinetics of their release are important for understanding those effects. The aim was to study the kinetics of the release of phenolic compounds from apples during in vitro simulated gastrointestinal digestion by using modified equations of first- and second-order kinetics. 35% and 67% of total phenolic compounds were released in the gastric phase, and 26% and 27% in the intestinal phase (peel and flesh, respectively). Intensive release of anthocyanins, flavan-3-ols, dihydrochalcones, phenolic acids, and flavonols occurred in the first 10 min of gastric digestion. In intestinal digestion, flavan-3-ols and anthocyanins were not identified; the dihydrochalcone amount decreased, while phenolic acids and flavonols showed stability. Concentrations at the endpoint of the release (c∞) were determined with kinetic equations fitted well to the experimental data (cexp) (r2 = 0.9973 and 0.9946 for first- and second-order). The half-life for released phenolic subgroups in gastric digestion was up to 3.5 (first-order kinetics) or 2.5 min (second-order), or in intestinal digestion up to 20.9 (first-order) or 32.3 min (second-order). Modified equations reported here for the first time fit well with the experimental data.