Determination of Antioxidant Activity and the Contents of Polyphenols and Flavonoids of Apples by Simulated Gastrointestinal Digestion
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Abstract:
Three cultivars of apples (Fuji, Gala, and Granny Smith apples) were used as raw materials for the investigation. Bioactive substances were extracted by in vitro gastrointestinal digestion and organic solvent extraction method. The antioxidant activity, as well as polyphenol and flavonoid contents in the extract, were determined, and patterns in the changes and correlations among these three were analyzed. The results showed that after simulated gastrointestinal digestion, antioxidant activity and polyphenol and flavonoid contents of apples increased significantly (P < 0.05). The amount of released polyphenol reached a maximum level and remained stable during the one-hour gastrointestinal digestion. During gastric digestion, the maximum amount of released polyphenol was 1.36~1.76 times higher than that before gastric digestion. During intestinal digestion, the maximum amount of released polyphenol was 1.34~2.08 times higher than that before intestinal digestion. Apple polyphenols are mainly composed of free polyphenols, and the content of polyphenols in the organic solvent extract was more than that after the simulation of gastrointestinal digestion (P < 0.05). At the simulated gastric digestion phase, a strong correlation (r = 0.74~0.99，P < 0.05) was noted among antioxidant activity and polyphenol and flavonoid contents. However, at the intestinal digestion phase, the correlation among antioxidant activity and flavonoid and polyphenol contents was low (r = -0.47~0.47, P < 0.05). Simulating gastrointestinal digestion may cause changes in the content and structure of polyphenols, leading to increases in antioxidant activity and polyphenol and flavonoid contents.
