Screening of protease-producing marine yeasts for production of the bioactive peptides

Over 400 yeast strains from seawater and sediments were obtained, but only five strains named HN2-3, N13d, N13C, Mb5 and HN3-2 among them could form clear zones around their colonies on the double plates with 2.0% casein.Peptides in the hydrolysate produced by the proteases from strains HN2-3 and N13d had higher angiotensin I-converting-enzyme (ACE)-inhibitory activity.The two marine yeast strains were identified to be Aureobasidium pullulans according to the results of routine yeast identification and molecular methods.After purification of the proteases from the two marine yeast strains, it was found that the optimal pH for them was both 9.0, both of them were serine alkaline protease.However, the optimal temperature for the protease from the strain HN2-3 was 52℃ while that from strain N13d was 48℃.ACE-inhibitory activity of the peptides in the hydrolysate of shrimp protein produced by the purified protease from the strain HN2-3 was the highest while antioxidant activity in the hydrolysate of spirulina protein produced by the purified protease from the strain N13d was the highest.