Effect of different enzymes on compacting and physical quality characteristics of torula yeast (Candida utilis)

Abstract

The purpose of this study was to investigate the reaction between the yeast materials derived from Candida utilis (CU) and different enzymes, and to evaluate their interaction on physical pellet quality. In order to evaluate the effect of different enzymes on Candida utilis, three kinds of enzymatic products were used, to compare the influence of each enzyme on CU. Used enzymatic products were protease, endo/exo 1.3-beta-glucanase, and the mixture between those two products. A number of physical pellet quality parameters were analyzed to determine the enzymatic influence on hardness, underwater pellet swelling rate (UPS rate), moisture content, water activity (Aw), surface contact angle with water/oil. Ten diets were formulated with three different enzymatic dosages: the optimal dosage recommended by the producer, ten folds higher dosage and hundred folds higher dosage. Among three enzymatic products, the protease showed indication to influence changes on pellet quality when compared to endo/exo 1.3-beta-glucanase, mixture of protease and endo/exo 1.3-beta-glucanase. The results showed that among all enzymes, mixture of glucanase and protease had higher influences on P-max than single endo/exo 1.3-beta-glucanase and protease; The 1 dosage protease and 1 dosage mixture of protease and endo/exo 1.3-beta-glucanase increased the oil absorption rate; The water contact angle was significantly increased when optimal dosage (1 dosage) of protease and 100 dosages of endo/exo 1.3-betaglucanase were added; The 100 dosages added protease increased predominantly the tensile strength, while endo/exo 1.3-beta-glucanase containing 10 dosages significantly decreased the tensile strength; Endo/exo 1.3-beta-glucanase decreased the aW, while the increased dosage of protease up to 100 folds decreased the aW values; All enzymes increased the moisture content to different levels, but the effect of protease was more significant than other enzymes; the protease with 100 dosage dramatically decreased the UPS rate.