Effect of in vitro gastrointestinal digestion on phenolic compounds and the antioxidant activity of Camellia sinensis L. green tea from organic farming

Objectives. - The aim of this work is to study the effect of in vitro digestion on the contents of total polyphenols and flavonoids and the antioxidant activity of green tea (Camellia sinensis L.) from organic farming. Material and methods. - Optimization of the tea cooking conditions was carried out by a central composite design. The contents of total polyphenols and flavonoids of the undigested and digested plants were determined by spectrophotometric methods. Phenolic extracts of green tea and digested lyophilizes were analysed by Attenuated total reflection-Fourier transform infrared. Evaluation of the antioxidant activity was carried out by three methods: DPPH, ABTS, and CUPRAC. Results. - Digestion causes a decrease in the levels of total polyphenols and flavonoids. The spectra obtained during the ATR-FTIR analysis showed intense bands corresponding to the O-H bonds, and C = C, C-H, C-O, and C = C bonds confirmed the presence of the polyphenols. A gradual decrease in the intensity of the absorption bands was observed during the three phases of digestion. The study of the effect of in vitro digestion on antioxidant activity indicates decreased antioxidant activity during two digestive phases (salivary and intestinal) and a marked increase during the gastric phase compared to the extract of the undigested plant. Conclusion. - This study shows that the three phases of digestion reduce the levels of total polyphenols and flavonoids. Two phases of digestion (salivary and intestinal) cause a decrease in antioxidant activity, while an increase in this activity was observed in the gastric phase. (C) 2021 Societe francophone nutrition clinique et metabolisme (SFNCM). Published by Elsevier Masson SAS. All rights reserved.