摘要：Background and Objective: Lactic acid bacteria with its proteolytic system hydrolyzes proteins to produce angiotensin-I-converting enzyme inhibitor during fermentation. A total of 108 indigenous lactic acid bacteria isolated from fermented food were screened based on proteolytic activity for the potential formation of angiotensin-I-converting enzyme inhibitory activity in fermented soy milk. Materials and Methods: Indigenous lactic acid bacteria (from tempe, kefir and breast milk) were screened based on proteolytic activity. Semi-qualitative screening of proteolytic activity of lactic acid bacteria was performed on skim milk agar. Thirty lactic acid bacteria isolates were further selected based on the formation of peptides in 11% reconstituted skim milk. A total of 10 lactic acid bacteria isolates with high proteolytic activity were selected as starter cultures for soy milk fermentation at 37°C until pH 4.6 was reached. Evaluation of fermented soy milk was performed by enumeration of lactic acid bacteria population, analyses of titratable acidity, soluble protein content, peptide content and determination of angiotensin-I-converting enzyme inhibitory activity. Results: Of 108 lactic acid bacteria isolates, 13.8% isolates had strong proteolytic activity and 15 isolates (13.8%) had moderate proteolytic activity based on clear zones formed surround the colony on skim milk agar after 48 h of incubation. The amount of peptide produced by isolates with strong and moderate proteolytic activity and the ability to reduce pH of soy milk varied among isolates. The pH value of 4.6 of fermented soy milk was reached after 24-48 h of incubation. Of 10 selected isolates, Lactobacillus plantarum 1W22408 and Lactobacillus fermentum R6 produced the highest angiotensin-I-converting enzyme inhibitory activity in fermented soy milk. Conclusion: Proteolytic activity and acidification ability of the lactic acid bacteria varied between isolates. Lactic acid bacteria isolates of Lactobacillus plantarum 1W22408 and Lactobacillus fermentum R6 were potential to be used as a starter culture to produce fermented soymilk which has angiotensin-I-converting enzyme inhibitory activity.
