Fermentation of various dietary fiber sources by human fecal bacteria

Eleven fiber-rich substrates were subjected to in vitro incubation with fecal bacteria from each of three adult male volunteers to assess substrate organic matter disappearance (OMD), short-chain fatty acid (SCFA) production, and the potential water holding capacity (PWHC) of fermented residues. Substrate OMD ranged from 83.3% (citrus pectin) to 5.8% (oat fiber). Total SCFA production (mmol/g substrate OM) was highly correlated to OMD and ranged from 9.64 (gum arabic) to 0.48 (oat fiber). Molar ratios of acetate:propionate produced during fermentation varied considerably among substrates, ranging from 1.5 for guar gum to 12.6 for citrus pectin. PWHC, an estimate of potential fecal bulking effects, was negatively related to OMD (r = -0.88) and ranged from 4.47 (oat fiber) to 0.71 (citrus pectin) g H2O/g substrate dry matter. In vitro fermentation techniques call be potentially useful predictors of in vivo responses to dietary fiber sources.