Antioxidant activity of amaranth protein or their hydrolysates under simulated gastrointestinal digestion

Amaranth proteins were subjected to a simulated gastrointestinal digestion to evaluate the antioxidant activity of the products. A protein isolate (I) was first hydrolyzed with pepsin (Pe) (pH 2, 37 degrees C) and then with pancreatin (Pa) (pH 6, 37 degrees C). Different hydrolysis conditions were assayed and control reactions (without enzymes) were performed. Hydrolysis degree (HD) determined by TNBS method ranged from 13 to 37%. Soluble fractions in 35 mmol/L phosphate buffer, pH = 7.8 were obtained from freeze-dried samples, and antioxidant activity was evaluated by the ABTS(+) scavenging and the ORAC assays. Antioxidant activity increased significantly (p < 0.05) after simulated gastrointestinal digestion. According to the results, digestion conditions (Pe/protein: 1:10,60 min; and Pa/protein: 1:10,60 min) were selected and applied to an amaranth protein alcalase-hydrolysate (H) (HD = 29.2 +/- 1.3). After pepsin and pancreatin action (Hpepa), HD was 42.0 +/- 2.6, slightly higher than that of the digested isolate (Ipepa) (36.9 +/- 0.5). The corresponding soluble fractions exhibited different electrophoretic profiles (tricine-SDS-PAGE) and gel filtration chromatograms, evidencing the presence of different molecular species. Previous hydrolysis with alcalase did not improve the antioxidant activity after simulated gastrointestinal digestion according to the methodologies assayed. Both the protein isolate and the alcalase-hydrolysate showed a potential capacity to scavenge free radicals after gastrointestinal digestion, appearing as promising ingredients to formulate functional foods with antioxidant activity. (C) 2011 Elsevier Ltd. All rights reserved.