α-Galactosidase Activity and Oligosaccharides Utilization by Lactobacilli during Fermentation of Soy Milk

In this study, α-galactosidase activity and depletion of oligosaccharides by six standard probiotic lactobacillus cultures were evaluated under at incubation times (6, 12, 18, 24, 30 h) in soy milk medium fortified with whey protein concentrate (WPC70) at 1.5%. Reduction of stachyose was higher due to maximum production of α-galactosidase (α-gal) enzyme (133.65 U/mg) by Lactobacillus rhamnosus C6 as compared with the other Lactobacillus cultures and was highest at 30 h of incubation (3.03 mg/100 mL). The results of this study will allow selection of L. rhamnosus C6 culture in soy milk medium supplemented with whey protein concentrate (WPC70), which will enhance growth of Lactobacillus and also reduce whey separation during fermentation process. This culture also showed highest proteolytic activity (381.67 μg serine/mL) by hydrolyzing soy proteins and produce soy bioactive peptides, which have health beneficial activities. L. rhamnosus C6 strain showed maximum α-galactosidase production as well as reduction of oligosaccharides viz. raffinose, stachyose and sucrose mostly present in soy milk. However, Lactobacilus casei NCDC17 also exhibited similar activity during soy milk fermentation. WPC70 fortification enhanced bacterial growth providing nutrition to the bacteria and also increased physiological activity during fermentation in soy milk medium. These two strains can be selected for the development of functional soy foods like soy yoghurt, soy cheese, soy beverages and soy dahi.