Changes in Antioxidant Activity of Peptides Identified from Brown Rice Hydrolysates under Different Conditions and Their Protective Effects against AAPH-Induced Oxidative Stress in Human Erythrocytes

Four antioxidant peptides (Ile-Tyr, Leu-Tyr, Val-Tyr, and Tyr-Leu-Ala), identified from brown rice protein hydrolysates, showed strong ROO center dot and ABTS(center dot+) scavenging activities. Changes in the antioxidant activity of peptides and GSH (control) under different processing conditions, namely, NaCl, temperature, pH, and gastrointestinal proteases, were evaluated by the oxygen radical absorbance capacity assay and the Trolox equivalent antioxidant capacity assay. Results indicated that with the increase in NaCl concentration, temperature, and pH (beyond neutral), the antioxidant activity of the peptides decreased, while the decrease was lower than that of GSH. The antioxidant activity of the four antioxidant peptides changed slightly after in vitro digestion, indicating a relatively high digestion resistance. The protective effect on the oxidative damage model of 2,2-azobis (2-methylpropionamide)-dihydrochloride-induced human red blood cells was also studied. Leu-Tyr and Tyr-Leu-Ala could alleviate but not totally inhibit oxidative damage in red blood cells, and their protective effects were dependent on concentration.