Abstract: Porphyra haitanensis protein (PHP) was simultaneously hydrolyzed with papain and chymotrypsin to prepare antihypertensive peptides. The hydrolyate was fractionated by ultrafiltration, and the resulting fractions were evaluated for scavenging capacity toward 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radicals, ferric ion reducing antioxidant power (FRAP) and angiotensin converting enzyme (ACE) inhibitory activity. The bioactive peptides were identified by mass spectrometry (MS) as well as through search in the bioactive peptides (BIOPEP) and antihypertensive peptides (AHTPDB) databases, and their ACE inhibitory mechanism was elucidated by molecular docking. Additionally, the kinetics of enzymatic hydrolysis of PHP was studied. The results showed that among the eight fractions obtained after ultrafiltration, the fraction with molecular mass less than 0.5 kDa had the highest DPPH and ABTS cation radical scavenging capacity, the fraction with molecular mass less than 1 kDa had the highest FRAP value, and the fraction with molecular mass in the range of 500–1 000 Da had the lowest half-maximal inhibitory concentration (IC50) value ((2.21 ± 0.28) mg/mL). Totally, 14 bioactive peptides were identified, four of which were selected for molecular docking analysis, indicating that their amino acid sequences were and docking energy were AVP (?5.87 kJ/mol), GPL (?6.13 kJ/mol), LDY (?7.65 kJ/mol) and LGYL (?7.78 kJ/mol), respectively. The relative error between the hydrolysis degree of PHP predicted by the kinetic model of enzymatic hydrolysis and the experimental values was less than 10%. This study can provide reference for the preparation of bioactive peptides.

Key words: Porphyra haitanensis; angiotensin converting enzyme inhibitory peptides; molecular docking; enzymatic hydrolysis kinetics