Resistant Waxy Rice Dextrin as a Carbon Source for Selected Probiotic Bacteria

Resistant dextrin (RD) is a soluble dietary fiber that can promote human health by serving as a valuable carbon source for gut microbiota. The aim of this study was to investigate the potential of indigestible waxy rice dextrin as the carbon source for selected probiotic bacteria. RD was prepared by heating waxy rice starch in the presence of HCl (0.4% dry starch basis) at 170 °C for 1 h, followed by enzymatic hydrolysis. Fermentation of RD with Lactobacillus plantarum and Bifidobacterium bifidum was conducted on MRS media without glucose. Fermentability was evaluated by monitoring amylolytic enzyme activity, pH, lactic acid, and succinic acid production in a broth medium for 72 h. The amount of enzyme activity varied among strains. The maximum enzyme activity for Bifidobacterium bifidum was 0.24 units/ml after 24 hours, whereas the maximum enzyme activity for Lactobacillus plantarum was 0.39 units/ml after 6 hours. There was no significant change in the pH of the cultures, which dropped from 6.8 to 6.4. The amount of lactic acid and succinic acid that had accumulated in both strains peaked after 12 h of fermentation and then started to decline after 48 and 72 h. The results showed that fermentation of RD with both stains produced a higher lactic acid content than that of commercial RD. RD derived from waxy rice starch is a promising candidate for use as a prebiotic source.