Preparation of Casein Peptides with High Antioxidant Activity

Peptides with high antioxidant activity were prepared from casein by a two-step method, i.e., first preparation of casein hydrolysates by papain-catalyzed, and then modification of these hydrolysates by plastein reaction with papain. The antioxidant activities of casein hydrolysates and their modification products were evaluated by DPPH assay and ABTS assay. The optimum conditions for casein hydrolysis were casein concentration 5%, papain concentration 500 U/g casein, pH 4.5, temperature 45 ℃ for a hydrolysis duration of 2 h, and the optimal plastein reaction conditions were substrate concentration 50%, papain concentration 500U/g substrate, and temperature 30 ℃ for 5.5 h reaction. Capillary electrophoresis analysis confirmed that the compositions of antioxidant peptides were changed as a result of plastein reaction. The DPPH and ABTS scavenging activity of casein peptides were remarkably enhanced after enzymatic modification.