Protein Hydrolysates from Citrullus lanatus Seed: Antiradical and Hydrogen Peroxide-scavenging properties and kinetics of Angiotensin-I converting enzyme inhibition

This study investigated the in vitro antihypertensive, antiradical and hydrogen peroxide-scavenging properties of protein hydrolysates from Citrullus lanatus (watermelon) seed (CSPHs) obtained through enzymatic digestion. Proteins from watermelon seeds were isolated and enzymatically hydrolyzed with non-specific (alcalase), moderately specific (pepsin) and highly specific (trypsin) proteases, mimicking human gastrointestinal digestion. The hydrolysates were investigated for inhibitory property against angiotensin-I-converting enzyme (ACE) activity. Using N-[3-(2-furyl)acryloyl]-L-phenylalanyl-glycyl-glycine as the substrate, CSPHs showed concentration-dependent ACE inhibition (IC₅₀ 1.377 - 1.757 mg/mL) with peptic CSPH having the strongest ACE-inhibition followed by tryptic CSPH. Kinetic analysis revealed that peptic CSPH inhibited ACE activity in a mixed-type inhibition pattern while alcalase and tryptic CSPHs exhibited non-competitive inhibition mode. Peptic CSPH demonstrated the strongest DPPH radical-scavenging activity while tryptic CSPH showed the highest H₂O₂-scavenging property. These results show that protein hydrolysates from watermelon seed possess bioactivities that could be exploited in the management of hypertension.