Optimization of preparation of Candida utilis polypeptide by ultrasonic pretreatment and double enzyme method

Candida utilis is a high-yielding strain of single-cell protein and a good source of bioactive peptides. At present, the research on Candida utilis mainly focuses on using it as animal feed, which greatly limits the application of Candida utilis. The aim of this work was to study the enzymatic hydrolysis of Candida utilis by ultrasonic pretreatment double-enzymatic method to maximize the enzymatic hydrolysis yield. For this purpose, a response surface method (RSM) was used, with enzyme dosage, enzyme ratio, temperature, pH, and time as process variables. The analysis of variance (ANOVA) results suggested that enzyme ratio, temperature, and pH were the most significant factors affecting the polypeptide yield and degree of hydrolysis. Response surface modelling showed that optimal polypeptide yield and degree of hydrolysis were achieved at the ratio of enzyme (alkaline protease: trypsin) 1: 1.85, the enzymolysis temperature 51 degrees C, and the pH 10. The optimal yields of polypeptide and hydrolysis degree were 53.34% and 47.78%, respectively. After ultrafiltration of Candida utilis hydrolysate, the polysaccharide removal rate reached 57.09 +/- 2.69%, and the free radical scavenging activity was significantly improved. Infrared spectrum results showed that the Candida utilis polypeptides prepared in this study have obvious amide I, II, and III band structure. Therefore, ultrasonic-assisted double-enzyme method can be effectively used to prepare polypeptides from Candida utilis and has the potential to be applied in the industrial extraction of Candida utilis polypeptides to increase the added value of yeast.