Novel angiotensin I-converting enzyme inhibitory peptides from protease hydrolysates of Qula casein: Quantitative structure-activity relationship modeling and molecular docking study

Qula casein derived from yak milk was hydrolysed using various enzymes. Hydrolysates were withdrawn at different hydrolysis phases and were determined to their degree of hydrolysis (DH) and ACE (angiotensin I-converting enzyme) inhibitory (ACEI) activities. Using a 3 kDa ultra-filtration membrane, hydrolysates were fractioned into two ranges of molecular weight and permeated fractions were further investigated. A Lineweaver-Burk plot was used to explore the ACEI kinetics of the hydrolysates. Additionally, the peptides in the hydrolysates were identified using LC-MS/MS. We established four quantitative structure-activity relationship (QSAR) models for predicting potential ACEI peptides. Using in silico analysis, four novel ACEI peptides were identified and a molecular docking study further explored the potential ACEI activities. Based on the docking results, three new peptides (PFPGPIPN, KYIPIQ and LPLPLL) were chemically synthesized and their IC₅₀ values were determined. In conclusion, our study suggests that Qula casein may be a valuable source of ACEI peptides.