Screening, Probiotic Properties Evaluation and Application of ACE-inhibitory Peptide-producing Lactic Acid Bacteria

Objectives: To screen lactic acid bacteria (LAB) produced angiotensin-converting enzyme (ACE) inhibitory peptides and to evaluate their probiotic properties. Methods: Lactic acid bacteria were inoculated into skimmed milk, the proteolysis degree and ACE inhibition rate of fermented milk were determined by colorimetric assays. Two LAB (ZJUIDS09 and ZJUIDS11) that resulted in the highest proteolysis degree and ACE inhibition rate were selected, and their probiotic properties were evaluated, including acid resistance, bile salt resistance, antibiotic resistance, and antibacterial activity. The fermented milk produced by the two strains was treated with simulated gastrointestinal digestive juices, and their ACE inhibition rates were determined. Finally, the two strains were used as starter cultures in the fermentation of Holstein skim milk, Holstein whey, buffalo skim milk and buffalo whey, and the ACE inhibition rates of the fermented milk were determined. Results: The degrees of proteolysis of fermented milk produced by strain ZJUIDS09 and ZJUIDS11 were 5.79%±0.14% and 5.75%±0.10%, respectively. Their ACE inhibition rates were 87.39%±2.44% and 90.41%±0.99%, respectively. And their IC₅₀ were 0.31 and 0.25 mg/mL, respectively. Their ACE inhibition rates after digestion with simulated gastrointestinal juices were decreased to 70.13%±0.15% and 76.39%±2.91%, respectively. Strains ZJUIDS09 and ZJUIDS11 were resistant to acid and bile salt, exhibited antibacterial activity and antibiotic sensitivity, and were identified as Lactobacillus reuteri and Lactobacillus helveticus by 16S rDNA. Comparing Holstein skim milk, Holstein whey, Buffalo skim milk and Buffalo whey after strain fermentation, Holstein skim milk was the most suitable substrates for strains ZJUIDS09 and ZJUIDS11 to produce ACE-inhibitory peptides. Conclusion: Lactobacillus reuteri ZJUIDS09 and Lactobacillus helveticus ZJUIDS11 screened in this study had a strong ability to produce ACE inhibitory peptides and had the potential to develop fermented dairy products with blood pressure-lowering effect.