DEVELOPMENT AND COMPARATIVE EVALUATION OF STORAGE CHANGES IN PROBIOTIC SOY-YOGHURT

Abstract

The addition of probiotics in the fermentation of soy milk products will enhance the health and commercial values of soy milk and create more alternative soy products to the delight of consumers. The survival of Lactobacillus acidophilus and Bifidobacterium lactis probiotics, inoculated into cow milk (PCMY) and soymilk (PSMY) to produce yoghurts and stored for 30 days at 10 °C were evaluated. The physico-chemical characteristics, probiotic viability and sensory qualities of the yoghurts were assessed. The results of the proximate composition showed that PCMY had higher moisture (30.49 %), protein (3.49 %) and carbohydrate (62.31 %) contents than PSMY. At the end of storage, PCMY had higher lactic acid content (1.35 %) than PSMY (1.32 %). The sugar content of the yoghurts also decreased with storage (3 to 4 weeks). There was rapid increase in specific gravity of both PCMY (1.00 to 1.20) and PSMY (1.25 to 1.90). The viscosity of the yoghurts ranged from 1433 to 1673 cP for PCMY and 1467 to 1640 cP for PSMY. The increase in total microbial load was more pronounced in PSMY (2.0 to 4.4 log cfu/ml) than PCMY 1.1 to 3.1 log cfu/ml). The growth of Lactobacillus in PCMY (9.1 log cfu/ml) and PSMY (5.4 log cfu/ml) was higher than that of Bifidobacteria (6.3 and 5.1 log cfu/ml) during storage. PSMY was less preferred to PCMY in terms of taste, texture and overall acceptability because of the beany flavour and low viscosity. The probiotic yoghurt from soymilk was comparable to standard yoghurt with little difference. PSMY will serve favourably as functional milk product with little modification.