Abstract:To study the antioxidant activity of collagen peptides with different molecular weight obtained from pig skin hydrolyzed by alkaline protease and bromelain step by step under the condition of pH gradual change.After pretreatment of pig skin，alkaline protease and bromelain were used to hydrolyze the enzyme step by step.Three different molecular weight peptides，M ＜ 1 kDa and 1 kDa ＜ M ＜ 3 kDa，M ＞ 3 kDa，were obtained by ultrafiltration.The content of peptides was determined by flinophenol colorimetric method，and the scavenging effects of each peptide segment on DPPH radical，ABTS+radical，O2-radical and OH radical were evaluated.The antioxidant activity of each component peptide in vitro，and then the mice were given intragastrically with different molecular weight peptidyl hydrolysates.The activities of total SOD，Glutathion Peroxidase and catalase in serum of mice after gastric perfusion were measured by kit.Total antioxidant capacity and trace malondialdehyde content were used to evaluate the antioxidant activity of each peptide in vivo.According to the experimental data of antioxidant activity in vitro and in vivo，the order of antioxidant capacity of each peptide was smaller than that of 1 kDa component ＞ 1 kDa-3 kDa component ＞ greater than that of 3 kDa component.Under the condition of pH gradual change，the pig skin gum was hydrolyzed by alkaline protease and bromelain step by step.Proto-protein peptides have different degrees of antioxidant capacity in vitro and in vivo，and the smaller the molecular weight，the stronger the antioxidant activity，which can play a protective role in the body.