Measurement of Fermentation Products and Substrate Disappearance During Incubation of Dietary Fibre Sources with Human Faecal Flora

A staticin vitrofermentation system using fresh human faeces has been developed. Fermentability may be quantified by determining metabolites and substrate disappearance. Methods to measure hydrogen production by gas chromatography (GC), short chain fatty acids in the fermentation supernatants by GC, and neutral sugar content in the residues by high performance anion exchange chromatography have been developed. These methods have been examined by conducting experiments using dietary fibre sources of variable chemical composition. The results obtained from the different fermentation parameters measured were consistent and indicated the degradation patterns of the substrates tested. The poor fermentability of pea hulls was found to be due to a considerable quantity of highly crystalline cellulose. Oat bran fermentation was characterized by a fast degradation of mixed-linked β-glucans and starch, whereas in apple pomace and celery cell walls pectic substances were easily metabolized by the microflora. It was therefore concluded that the degradation of soluble polysaccharides is mainly determined by their chemical composition. Conversely, the fermentability of insoluble fibres is primarily related to their susceptibility to the faecal flora.In vitrofermentation experiments performed under well defined conditions offer an appropriate means to measure fermentability of dietary fibre rich substances.