Physicochemical Properties of Dioscorea opposita Thunb. Solution Fermented by Lactobacillus bulgaricus

The present study was designed to determine the physicochemical properties of yam (Dioscorea) solution fermented by L. bulgaricus, the protective effect of fermented Dioscorea opposita Thunb. on stomach lesions, and the possibility of its application to fermented dairy products. When the concentration of yam increased, the pH increased in raw powder samples but not in extracted powder samples. In 6% raw powder containing the sample, the viable cell counts showed a dramatic increase, whereas those in extracted yam powder significantly decreased in all concentrations during 32 h of fermentation. The viscosity of extracted yam powder showed a lower value than that of raw powder, which was maintained throughout the fermentation. The solution of Dioscorea opposita Thunb. raw powder showed a significantly higher allantoin content compared with the extracted powder (p<0.05). At 2% of added Dioscorea opposita Thunb., 0.65 mg/mL was contained in both samples; however, when 6% of Dioscorea opposita Thunb. was added, the amount of diosgenin increased up to 1.9 mg/ mL. When 200 mg of powder/kg body wt. was injected, gastric lesions were apparently reduced compared with those of control rats. With 100 mg/kg body wt. injected into rats, the protective effect was a little lower than that in 200 mg/kg body wt. Based on these data, the present study indicated that yam powder fermented by L. bulgaricus showed a protective effect on gastric lesions in rats; therefore, it may be included as an added ingredient in yogurt manufacture.