Effects of transglutaminase treatment on Lactobacillus casei viability, physicochemical and sensory properties of nonfat stirred yoghurt

The effect of microbial transglutaminase concentration, amount of sodium caseinate incorporation and storage time on Lactobacillus casei viability in nonfat stirred yoghurt and it`s physicochemical and sensory properties were investigated using response surface method (RSM). Enzyme concentration, amount of sodium caseinate and storage time were in the range of 0-2 Unit per gram of milk protein, 0-1.27 percent and 1-19 days, respectively. The statistical analysis of results showed that increase in enzyme concentration increased the viability of Lactobacillus casei and Lactobacillus bulgaricus viability significantly (P<0.05) and decreased the syneresis. Addition of sodium caseinate caused an increase in acidity and moisture content of samples. As well, during the storage time, pH and moisture content were decreased and acidity was significantly increased (P<0.05). According to sensory evaluation results, the higher the sodium caseinate content, the lower was the color score of treatments. As the concentration of transglutaminase increased, flavor scores for yogurt samples increased. The optimum conditions for the production of yogurt was obtained using 1.41 Unit enzyme per gram of milk protein, 0.13 percent sodium caseinate with a storage period of 15 days. Under these conditions the predicted Lactobacillus casei and Lactobacillus bulgaricus counts were 8.33 and 8.35 logarithmic cycle respectively, the percentage of syneresis was 6.72, color and overall acceptability rate were 3.37 and 3.87 out of 5, respectively.