Abstract: Angiotensin converting enzyme （ACE） inhibitory peptide was prepared from Flammulina velutipes by ultrasonic-assisted enzymolysis, providing the basis for further processing of Flammulina velutipes. The enzyme for preparing ACE inhibitory peptide of Flammulina velutipes was screened, and the optimal pH for separating active peptide by isoelectric point precipitation was optimized. With ACE inhibition rate as the response value, a single factor test was carried out with five factors, including liquid to material ratio, ultrasonic time, and enzyme dosage, and a response surface test with four factors and three levels was designed. The results showed that the best protease for preparing ACE inhibitory peptide of Flammulina velutipes was trypsin, and the best pH for precipitating active peptide was 6.5. The optimal preparation condition of ACE inhibitory peptide was as follows： ultrasonic power of 250 W, enzymolysis temperature of 37 ℃, enzymolysis pH of 8, liquid to material ratio of 40∶1 （mL/g）, and ultrasonic time of 5 min. Enzyme addition was 1.2% （g/g） of Flammulina velutipes sample, and enzymolysis time was 90 min. ACE inhibitory peptides were classified and their activity was analyzed using ultrafiltration separation method. Under this condition, the ACE inhibitory rate of Flammulina velutipes peptide was （65.36 ± 1.53） %; peptides with a molecular weight of <3 kDa had the highest ACE inhibition rate.

Key words: Flammulina velutipes, ACE inhibitory peptide, ultrasonic-assisted enzymatic method, response surface optimization