RESPONSE SURFACE METHODOLOGY FOR OPTIMIZING FERMENTATION CONDITIONS OF GOAT YOGURT WITH BIFIDOBACTERIUM BIFIDUM AND LACTOBACILLUS CASEI

Abstract

Probiotic bacteria have been widely applied in food industry, especially in dairy product and functional food. The objective of present work was to optimize fermentation conditions of goat milk with B. bifidum and L. casei. A Box-Behnken design was employed to investigate the effects of fermentation temperature, strain ratio and inoculum size on viable counts of B. bifidum and L. casei, total bacteria counts and sensory value during fermentation on the basis of S. thermophilus and L. bulgaricus as starter cultures. The results showed that the quality of goat yogurt was best at the conditions of 41oC, strain ratio, 2:1:1; inoculum size, 6%. Under the optimum conditions, the viable counts of B. bifidum, L. casei, total bacteria and sensory value reached at (1.31±0.07) ×108 cfu/mL, (2.67±0.09) ×107 cfu/mL, (1.62±0.06) × 109 cfu/mL and 7.52±0.11, respectively. There was no significant difference between the predicted value and the verification results (p<0.05). The optimum fermentation conditions shown positive effects on the response value which can be propose for goat milk fermented productions.