Preparation of the bioactive peptides from porphyra yezoensis and their hydroxyl radical scavenging activity
The proteases trypsin, pepsin, papain, alcalase and neutrase were screened for the optimum hydrolysis of the Porphyra yezoensis protein. The hydrolysis conditions were optimised using single-factor trials and response surface analysis. The hydroxyl radical scavenging activity and molecular weight of the hydrolysates were examined. Alcalase had the best hydrolysis effect, and the optimum conditions for hydrolysis were as follows: substrate concentration, 5 mg/mL; enzyme amount, 9.6×103 U/g; pH 8.5; reaction temperature, 55°C; and hydrolysis time, 4 h. The hydroxyl radical scavenging activity of the enzymatic hydrolysates was 67.88%, and the half maximal inhibitory concentration was 1.072 mg/mL. More than 70% of the peptides were small peptides with molecular weights less than 1500 Da.
Bioactive peptides exhibit an antioxidant activity. In 1956, Harman proposed free radical theory, which states that many human diseases are related to free radicals (1). Antioxidant peptides effectively clear excessive reactive oxygen free radicals in the body to prevent lipid peroxidation, which has become a hot area of current research (2–4). Under suitable conditions, bioactive peptides with antioxidant capacity from sea animal and plant protein can be prepared by enzymatic hydrolysis (5–7). Some studies focused on other sources such as sardine head and internal organ (8), oyster protein (9), white shrimp head and thorax (10) and lactic acid-fermented shrimp waste (11). These studies used protease hydrolysis to prepare active peptides of low