Abstract: Porphyra yezoensis protein hydrolysate, prepared enzymatically under specific and controlled conditions, was found to be dominated by small peptides with molecular mass less than 1 000 Da. It had inhibitory activities against α-glucosidase and dipeptidyl peptidase IV (DPP-IV) and was able to tolerate pH, temperature and gastrointestinal digestion. The enzymatic hydrolysate was separated and purified consecutively by ultrafiltration, nanofiltration and gel filtration chromatography. Two bioactive peptides, Ala-Pro and Pro-Gly-Gly-Val, were identified by ultra-high performance liquid chromatography-electrospray ionization-quadrupole-time of flight-mass spectrometry (UPLC-ESI-Q-TOF-MS). Peptides corresponding to the sequences with a purity of 99.69% were separately synthesized and their inhibitory activities against the two enzymes were characterized. The results showed that Pro-Gly-Gly-Val was a double-enzyme inhibitory peptide with an IC50 of 18.60 mmol/L for α-glucosidase and of 17.80 mmol/L for DPP-IV. Ala-Pro had an inhibitory effect only against DPP-IV with an IC50 of 4.65 mmol/L.

Key words: Porphyra yezoensis; characterization of enzymatic hydrolysate; α-glucosidase inhibitory activity; dipeptidyl peptidase IV inhibitory activity; separation and purification; composition identification