Antioxidant Activity and Quality Evaluation of Probiotic Soymilk Produced with Lactobacillus rhamnosus Yoba as Starter Culture

Dairy product has always been the common means of delivering probiotics in the western world. However, as milk is not always readily available, or is expensive in most communities in Nigeria, soymilk is considered as a suitable economical substitute for cow’s milk and an ideal nutritional supplement for lactose-intolerant population. This study aims to determine the antioxidant activity and quality of probiotic soymilk fermented with Lactobacillus rhamnosus Yoba. Soymilk was fermented with Lactobacillus rhamnosus, incubated at 400C for 24 h. Samples were collected at 0, 4, 8, 12, 16, 20, and 24 hours to monitor the proliferation of the probiotics, pH, acidity, antioxidant activity and sensory properties of the fermented and unfermented soymilk. The results showed that beyond the 12 h of fermentation, all concentrations of the sugar used for the fermentation attained the recommended microbial load 106CFU/g of probiotic microorganisms. There was also a drastic drop in the pH of all the samples from the 12 h of fermentation likewise the acidity of the samples. The antioxidant activity showed a significant increase in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging ability, β carotene bleaching assay and 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) scavenging effects from 84.065% to 86.224%, 10.68 to 14.036(mg/ml) and 67.512 to 67.935% after fermentation respectively. There was also a decrease in the total peroxide and ferric reducing antioxidant property (FRAP) from 12.40 to 8.20 (mleq/kg) and 87.116 to 61.702% inhibition respectively. The panelists preferred the taste and flavor of the unfermented soymilk. However, the texture and mouth feel of the fermented soymilk was more preferable. These findings point to the possibility that to improve traditional fermented foods in Nigeria with added probiotic health features it is needful to incorporate well documented probiotics into our food matrix to aid the spontaneous fermentation system.