Suppressive Effect of Fructooligosaccharides on the Generation of Volatile Methanethiol in a Fecal Incubation Method and Human Feces

Abstract

Thirteen dietary substances were examined by a modified in vitro fecal incubation method, with an additional amounT of L-methionine (Met) present, to assess their suppressive effect on the generation of volatile methanethiol (MeSH) in feces. Three kinds of carbohydrates (glucose, inulin, and fructooligosaccharides (FOS)) were found to suppress McSH generation to a level below half that of the control after 3-hr incubation, and it was suggested that the effect wasn't simply derived from the decrease of pH during incubation. In a human in vivo study, FOS-tofu intake for 2 weeks was found to reduce both the frequency of MeSH detection (5/11→3/11) and the average concentrations (3.57 ± 4.81→. 1.02 ± 1.92 ppm) of fecal MeSH as compared to no intake. A comparison of the fecal bacterial counts between MeSH. undetectable (MeSH^-) and MeSH-detectable (MeSH⁺) groups showed interesting features that the counts of ^{Bifidobacterium} indicated a significant increase (p = 0.002) only between the MeSH^- groups in the FOS-tofu intake and non-intake periods, and the frequencies of Bacillus detection showed a high number in the MeSH⁺ group of the nonintake periods.