Abstract: Crude cell-envelop proteinase extracted from Lactobacillus casei cells was purified/fractionated by DEAE-Sephadex A-25 and subsequent Sephadex G-100 column chromatographies. Two cell-envelop proteinase fractions, named as CEP-1 and CEP-2, were obtained, of which the activity was 12.50 U/mg and 16.67 U/mg, the purification folds 50 and 66.68, and the recoveries 33.61% and 55.17%, respectively. The hydrolysis characteristics of CEP-1 and CEP-2 on α-casein and β-casein under different conditions of hydrolysis time and substrate concentration were assessed in terms of angiotensin-I-converting enzyme (ACE) inhibitory activity and superoxide anion radical scavenging activity of hydrolysates. Both CEP fractions resulted in casein hydrolysates with obvious ACE inhibitory activity and superoxide anion radical scavenging activity. Maximum ACE inhibitory activity was achieved after 6 h hydrolysis of α-casein at an enzyme/substrate ratio of 1:10 by CEP-2, reaching 84.66%. Theβ-casein hydrolysate obtained after 4 h of hydrolysis with an enzyme/substrate ratio of 1:40 revealed the best superoxide anion radical scavenging activity with a 0.2138 mg/mL IC50.

Key words: cell-envelop proteinase (CEP), casein hydrolysate, ACE-inhibitory activity, antioxidant activity