Screening potential hypertensive peptides using two consecutive bioassay-guided SPE fractionations and identification of an ACE inhibitory peptide, DHSTAVW (DW7), derived from pearl garlic protein hydrolysate

The pearl garlic (Allium sativum L.) protein (PGP) was digested using pepsin, trypsin, α-chymotrypsin, thermolysin, and simulated gastrointestinal digestion. The α-chymotrypsin hydrolysate showed the highest angiotensin-I-converting enzyme inhibitory (ACEI) activity, with an IC50 value of 190.9 ± 11 µg/mL. A reversed-phase C18 solid-phase extraction (RP-SPE) cartridge was used for the first fractionation, and the S4 fraction from RP-SPE showed the most potent ACEI activity (IC50 =124.1 ± 11 3 µg/mL). The S4 fraction was further fractionated using a hydrophilic interaction liquid chromatography SPE (HILIC-SPE). The H4 fraction from HILIC-SPE showed the highest ACEI activity (IC50 =57.7 ± 3 µg/mL). Four ACEI peptides (DHSTAVW, KLAKVF, KLSTAASF, and KETPEAHVF) were identified from the H4 fraction using liquid chromatography-tandem mass spectrometry (LC-MS/MS), and their biological activities were appraised in silico. Among the identified α-chymotryptic peptides, DHSTAVW (DW7), derived from I lectin partial protein, exhibited the most potent ACEI activity (IC50 value of 2.8 ± 0.1 µM). DW7 was resistant to simulated gastrointestinal digestion, and it was classified as a prodrug-type inhibitor according to the preincubation experiment. The inhibition kinetics indicated that DW7 was a competitive inhibitor, which was rationalized by the molecular docking simulation. The quantities of DW7 in 1 mg of hydrolysate, S4 fraction, and H4 fraction were quantified using LC-MS/MS to give 3.1 ± 0.1, 4.2 ± 0.1, and 13.2 ± 0.1 µg, respectively. The amount of DW7 was significantly increased by 4.2-fold compared with the hydrolysate, which suggested that this method is efficient for active peptide screening.