Effect of Dioscorea opposita Thunb. (yam) supplementation on physicochemical and sensory characteristics of yogurt.

A study was conducted to examine the physicochemical, microbial, and sensory properties of yogurt made by supplementing powdered yam Dioscorea opposita Thunb. (YPT) at different concentrations (0.2, 0.4, 0.6, and 0.8%, wt/vol) into milk, which was pasteurized and then fermented at 43°C for 6 h and stored for 16 d. The pH values of all samples decreased, whereas viscosity values and mean microbial counts increased during storage. The L* and a* color values (indicators of lightness and redness, respectively) of yogurt samples were not remarkably influenced by adding YPT, whereas the b* values (indicating yellowness) significantly increased with the addition of YPT at all concentrations at 0 d of storage, probably due to the original yellow color of yam powder. In functional component analyses, when the concentration of YPT increased, the amount of allantoin and diosgenin proportionally increased. The content of allantoin was 3.22 and diosgenin 4.69 µg/mL when 0.2% (wt/vol) YPT was supplemented and did not change quantitatively during the storage period (16 d). The sensory test revealed that the overall acceptability scores of YPT-supplemented yogurt samples (0.2 to 0.6%, wt/vol) were quite similar to those of the control throughout the storage period of 16 d. Based on the data obtained from the present study, it was concluded that the concentrations (0.2 to 0.6%, wt/vol) of YPT could be used to produce YPT-supplemented yogurt without significant adverse effects on physicochemical, microbial, and sensory properties, and enhance functional components from the supplementation.

Physico-chemical characterization of a new heteropolysaccharide produced by a native isolate of heterofermentative Lactobacillus sp. CFR-2182.

A heterofermentative Lactobacillus sp. CFR-2182 was isolated from dahi samples and it was found to produce 8.0 and 20.5 g/L heteropolysaccharide (HePS) in EPS medium (a simplified synthetic medium) and modified MRS broth, respectively, after 72 h at 30 degrees C. The total carbohydrate, reducing sugar and moisture contents of the purified HePS were 74, 10.6 and 2 g, respectively, per 100 g on dry weight basis. The HePS produced in EPS medium had glucose and mannose in 17:1 ratio. The HePS was non-gelling and non-film forming type. It was completely soluble in water and 1 N sodium hydroxide solution. Gel permeation chromatography and HPLC analysis indicated considerable heterogeneity of the HePS, having three fractions with molecular weights ranging from 3.3 x 10(4) to 1.32 x 10(6) Da. The enzymatic hydrolysis of the HePS with pullulanase and alpha-amylase [with alpha(1-->4) linkage] indicated the presence of alpha(1-->6) and traces of alpha(1-->4) linkages, respectively. NMR analysis of the EPS revealed unique chemical shifts.