In this study, we propose to develop of soy yogurt with enhanced isoflavone-aglycone contents and antioxidant activity by potential probiotics Lactobacillus plantarum LAB 12-01.

1. The potential probiotic of a total of approximately 300 lactic acid bacteria (LAB) isolated from the fermented foods such as kimchi and fermented plant extract beverage was evaluated. These isolates were classified as Lactobacillus plantarum based on phylogenetic analysis by their 16S rDNA sequences. In addition, the L. plantarum LAB 12-01 showed a significant survival rate range 92.56% to 62.22% under artifical gastric acid conditions at pH 2.5 for 2 hr and 4 hr. In addition L. plantarum LAB 12-01 appeared the antioxidant activity remarkable than other L. plantarum strains. The levels of total phenolics and isoflavone-aglycone contents markedly increased after 48 hr of fermentation, while isoflavone-glycosides and -malonylglycosides contents decreased. In particular the levels of daidzein glycitein and genistein were present at concentrations of 300.85 μg/g 9.15 μg/g and 74.20 μg/g after 48 hr of fermented by L. plantarum LAB 12-01.

2. The change of physiochemical property, total phenolics and isoflavone contents during the soy yogurt fermentation by L. plantarum LAB 12-01 was investigated. The optimal fermentative condition of soy yogurt in the lactic fermentation was determined as following: 35℃ of temperature, 5.0% of seed volume and 10.0% of sucrose. The levels of total phenolics and isoflavone contents and the antioxidant activities were higher in SPM than in SM. In particular, the highest levels of daidzein, glycitien, and genistein were present at concentrations of 91.50 μg/g, 12.34 μg/g, and 61.39 μg/g after 48 hr of the fermented SPM.

3. From this result, we suggest that the high antioxidant activity of SPM yogurt might be related to the markedly higher levels of total phenolics and isoflavone-aglycone contents achieved during fermentation. In particular, this study suggest that the SPM yogurt extracts could be used as a potential source of natural antioxidants in certain food applications. Further studies are needed to determine the various biological activities, such as in vitro, in vivo and the applied animal experiments.