Different substrates and methane producing status affect short-chain fattyacid profiles produced by in vitro fermentation of human feces

Five different substrates, i.e., lactulose, rhamnose, cornstarch, guar and ileostomy effluent, were used to determine whether methane producing status alters the production of short-chain fatty acids (SCFA) in methane produce rs (MP; n = 6) and nonproducers (MNP; n = 5). Fecal samples from MP and MNP were fermented with the five substrates using an in vitro fermentation met hod. Subjects with a mean breath methane concentration > 0.045 mu mol/L abo ve ambient air were classified as MP. Fermentation was stopped and samples were obtained at 3, 5 and 24 h. An HPLC method was used to measure the SOFA , acetate, propionate, isobutyrate, butyrate, valerate and isocaproate. A s ignificant interaction between methane producing status and time for acetat e production from lactulose was observed. There were no differences in ferm entation of the four remaining substrates between MP and MNP, but there wer e significant differences among substrates in the two groups combined. Acet ate production from lactulose was significantly greater than from the four other substrates, whereas that from ileostomy effluent was significantly le ss than the four other substrates. The amount of propionate produced from r hamnose was significantly higher than from the other substrates. The amount of butyrate produced from lactulose and cornstarch was significantly highe r than from the other substrates. We conclude that differences exist in the fermentation patterns of lactulose, rhamnose, cornstarch, guar and ileosto my effluent. Methane producing status may influence fermentation patterns o nly of substrates that are largely fermented to acetate and not others.