Effect of addition of sodium caseinate and peppermint extract on viability of Lactobacillus casei and physicochemichal properties and antioxidant activity of non-fat probiotic yogurt

Response surface methodology was employed to investigate the combined effects of sodium caseinate (0–4%)، peppermint extract (0-0. 2 %) and refrigerated storage on functional، chemical and antioxidant activity of nonfat-set yogurt. The second-order polynomial model was fitted to the physicochemical properties of runs as the responses. Analysis of variance revealed that the quadratic models are well adjusted to predict the experimental data. Lack-of-fit tests were not significant and determination coefficients (R2) and adjust determination coefficient were high. The statistical analysis of the results showed that addition of sodium caseiante had significant effect on syneresis، water holding capacity (WHC)، apparent viscosity and L. casei counts (P<0. 05) and also addition of peppermint extract showed significant effect on apparent viscosity، L. casei counts (P<0. 05) and refrigerate storage had significant effect on pH، acidity، syneresis، WHC، apparent viscosity، probiotic count and antioxidant activity (P<0. 05).