Effect of wheat germ and rice bran protein concentrate on the qualitative properties of probiotic yoghurt

In present research, effect of addition of wheat germ protein concentrate (WGPC) and rice bran protein concentrate (RBPC) on the physicochemical properties and probiotic survival of yoghurt during storage was investigated. Treatments and optimization were determined by Design Expert 10 software using RBPC (0, 0.25, and 0.5 percent) and WGPC (0, 0.5, and 1 percent) mixture as independent variables. Results showed addition of RBPC and WGPC to probiotic yoghurt, increased pH and decreased acidity (p<0.05). Firmness of yoghurt samples increased by WGPC addition. The highest and the lowest firmness were belonged to sample No.1 (1% WGPC and 0.5% RBPC) and sample No.4 (0.5% RBPC), respectively. In term of synersis, results showed that WGPC decreased synersis but RBPC had no significant effect. Sensory evaluation revealed that protein concentrate addition caused a reduction of total acceptance and RBPC had more effect on score reduction. In term of probiotic survival, all of samples except sample No.4 had >106 cfu/gr during 21 days of storage. Results of probiotic loss revealed that protein concentrate addition decreased probiotic loss. In conclusion, regarding studied factors and numerical optimization, it was revealed that 1% WGPC could improve quality of probiotic yogurt.