Functional and technological application of probiotic L. casei PLA5 in fermented soymilk

This study was designed with an objective to develop a probiotic dietary adjunct using soymilk (Harit soya variety). Soymilk is fermented with probiotic strain Lactobacillus casei PLA5 (Accession no KJ726650) which have been isolated from Churpe -a traditional fermented milk product. During various fermentation time, changes in pH, titratable acidity and viable count were evaluated and were compared with the soymilk fermented with commercial probiotic L. casei strain Shirota. Changes in β-glucosidase, β-galactosidase and proteolytic activity during the fermentation of probiotic soymilk were examined. In addition, antioxidative activities including DPPH (1, 1-diphenyl-2-picrylhydrazyl) free radical scavenging activity, total flavonoids and polyphenols determination were also investigated. Growth of probiotic L.casei PLA5 in soymilk via supplementation with prebiotics was also studied and shelf life of probiotic soymilk was periodically checked for 14 days. Log CFU/ml of soymilk fermented with L. casei PLA5 was found to be significantly higher than soymilk fermented with L. casei strain Shirota. β-glucosidase (3.40 U/mg) activity was found to be higher than β-galactosidase (0.14U/mg) activity in soymilk during fermentation. Antioxidative activity increased during fermentation; however, H₂O₂-scavenging effect decreased. Polyphenols content declined from 14.01 to 6.01 mg/100 ml whereas, flavonoid content varied between 1.46-3.52 mg/ml during fermentation. Increase in bioavailability of minerals was also observed in fermented soymilk. A significant enhanced growth (p<0.05) of L. casei PLA5 was observed with maltodextrin and fructooligosaccharide by 1.24 and 1.09 log CFU/ml respectively. Bacterial counts remained constant and above 107 CFU/ml during the storage period of 14 days at refrigeration temperature. These results suggest that soymilk prepared from probiotic L. casei PLA5 strain had high antioxidant capacity and promising enzymatic potential and could be commercialized as probiotic beverage.