A Study of the Fermentation of Dietary Fibre by Human Colonic Bacteria GrownIn Vitroin Semi-continuous Culture

An in vitro study of human colonic bacterial metabolism was made using a semi-continuous fermentor inoculated with human source faeces and fed three times daily with a medium high in dietary fibre and low in soluble carbohydrate. After an initial period of 3-4 d the fermentor pH and volatile fatty acid concentrations and molar proportions generally stabilised within a narrow range. Between 60 per cent and 70 per cent of the dietary fibre added daily was fermented. Measurements and calculations aimed at determining the fermentation balance indicated that the hydrogen and methane productions were lower than expected and suggest that acetate is formed partly by reduction of CO 2 or by homoacetate fermentation. The cultures established in the fermentor may serve as a reasonable model for the fermentation in the human colon. Keywords: Human colonic bacteria: Fermentation balance.