Quality characteristics of soy yogurt produced using proteases and mixed microbial consortia

Abstract

In this study, we examined the quality characteristics of soy yogurts produced using two proteases(Flavourzyme (R) and Neutrase (R)) and the mixed microbial consortia of Lactobacillus bulgaricus and Streptococcus thermophilus (two-mixed) and Lactobacillus acidophilus, Bifidobacterium lactis, and S. thermophilus (three-mixed). The viscosity was the highest in the untreated yogurt. Among the proteolyzed samples, those treated with Flavourzyme (R) for 20 min showed the highest viscosity, whereas the samples treated with Neutrase (R) for 30 min and cultured with three-mixed microbial consortia showed the lowest viscosity. The numbers of viable bacteria in the Flavourzyme (R)-treated samples were slightly greater than those in the Neutrase (R)-treated samples. The number of viable bacteria increased as hydrolysis time increased. The organic acid content was higher in the three-mixed group than in the two-mixed group, and it was higher in the Flavourzyme (R)-treated samples than in the Neutrase (R)-treated samples. Among the Flavourzyme (R)-treated samples, the three-mixed group showed higher total free amino acid content than the two-mixed group. In contrast, among the Neutrase (R)-treated samples, those cultured with both mixed microbial consortia produced the similar amounts of free amino acids. The above results showed that proteolytic treatment promoted the growth of lactic acid-producing bacteria. Soy yogurts produced using Flavourzyme (R) and three-mixed microbial consortia were thought to be more desirable because of more organic acids and free amino acids than those produced using Neutrase (R) and two-mixed microbial consortia.