Antioxidant properties of green tea extract incorporated to fish gelatin films after simulated gastrointestinal enzymatic digestion

A green tea aqueous extract was prepared and blended at different percentages (2, 4 and 8%) with a commercial fish-skin gelatin in order to provide gelatin films with antioxidant capacity. This green tea extract proved to be an efficient antioxidant at non-cytotoxic concentrations. Gelatin films with green tea extract were subjected to enzymatic digestion with pepsin (gastric digestion) and with pepsin, trypsin and chymotrypsin (gastrointestinal digestion). The gelatin matrix was efficiently hydrolysed during gastrointestinal digestion and protein hydrolysates composed of low molecular weight peptides, regardless the content of green tea extract, were obtained in all the formulations. High percentages of total polyphenols were recovered from the films with green tea extract after gastrointestinal digestion, although a significant degradation of the major catechins of the green tea (EGCG and EGC) was observed. The increase of the content of green tea extract in the film formulation gave an increase in the antioxidant activity released from the film samples after enzymatic digestion. 85-100% of the maximum expected antioxidant activity was recovered after both gastric and gastrointestinal digestion in spite of the degradation observed of EGCG and EGC.