Probiotic Bacillus spp. in Soy-Curd: Nutritional, Rheological, Sensory, and Antioxidant Properties.

UNLABELLED: The focus of this study was to coculture probiotic Bacillus spp. with dairy starter cultures namely, Streptococcus thermophilus and Lactobacillus bulgaricus for enhanced nutritional properties of soy-curd. Subsequently, rheological, sensory, and antioxidant properties of soy-curd along with mineral as well as fatty acid composition were analyzed. Data revealed an increase in the cell viability of probiotic Bacillus spp. on coculturing rather than as mono-culture. Proximate analysis showed higher nutritional value along with increased trace elements. UFA/SFA ratio, rheology, and sensory properties of probiotic soy-curd were in the acceptable range. Probiotic soy-curd showed higher antioxidant activity as measured by the ability to scavenge free radicals. No significant difference in the overall quality within the probiotic products was observed. However, B. flexus MCC2427 cocultured product displayed slightly better attributes than other samples. In general, the results suggest that soy-curd can be a suitable carrier for probiotic Bacillus spp. and the enhanced nutritional and antioxidant properties could be of additional advantage to combat malnutrition problem. PRACTICAL APPLICATION: In order to supply consumers with intriguing probiotic products for improving health benefits, several criteria including technological and functional properties should be considered as a quality control measures. Further, a meaningful level of probiotics has to be viable to exhibit beneficial effect. Hence, present work has been carried out to improve the quality of soy-curd by supplementation of probiotic Bacillus spp. These Bacillus spp. are well characterized native probiotic cultures with potential functional attributes including antimicrobial, antioxidant, anticholesterol activity (Shobharani and Halami 2014). Hence, the application of these cultures will encourage for development of food product with wider health benefits.

Aspartate biosynthesis is essential for the growth of Streptococcus thermophilus in milk, and aspartate availability modulates the level of urease activity.

We investigated the carbon dioxide metabolism of Streptococcus thermophilus, evaluating the phenotype of a phosphoenolpyruvate carboxylase-negative mutant obtained by replacement of a functional ppc gene with a deleted and inactive version, Deltappc. The growth of the mutant was compared to that of the parent strain in a chemically defined medium and in milk, supplemented or not with L-aspartic acid, the final product of the metabolic pathway governed by phosphoenolpyruvate carboxylase. It was concluded that aspartate present in milk is not sufficient for the growth of S. thermophilus. As a consequence, phosphoenolpyruvate carboxylase activity was considered fundamental for the biosynthesis of L-aspartic acid in S. thermophilus metabolism. This enzymatic activity is therefore essential for growth of S. thermophilus in milk even if S. thermophilus was cultured in association with proteinase-positive Lactobacillus delbrueckii subsp. bulgaricus. It was furthermore observed that the supplementation of milk with aspartate significantly affected the level of urease activity. Further experiments, carried out with a p(ureI)-gusA recombinant strain, revealed that expression of the urease operon was sensitive to the aspartate concentration in milk and to the cell availability of glutamate, glutamine, and ammonium ions.