Abstract
Dietary fibres may act as prebiotics, i.e. stimulation of growth of health-promoting probiotic bacteria such as bifidobacteria and lactobacilli. Fermentation of carbohydrates by the gut microflora generates short-chain fatty acids (SCFA), of which particularly butyric acid is considered as beneficial for the health. In vitro fermentations of fibres with human faeces have frequently been used for comparison of fibres with respect to the formation of SCFA, analysed by GC or HPLC. In contrast to techniques directed against analyses of specific compounds, the use of LC- and/or GC-MS will generate an overall metabolite profiling, a ""metabolic footprint"". Such data may provide valuable information about the function of the microbiota, as a supplement to information gained from DNA-analyses, telling which bacterial genera and species that are present. A range of fibres have been screened by in vitro batch fermentations with faeces from infants (3-7 months age) and adults. The fibres include polysaccharides or selected fibre fractions, such as β-glucans, arabinoxylan and poly-uronic acids (pectin, alginate). The commercial prebiotic inulin was included for comparison. SCFA were monitored by HPLC-analyses, while a complete metabolite profiling was achieved by use of GC-MS. Independent of the faeces source, the highest amount of SCFA, with acetate as the dominating acid, was produced from inulin and a pectin fraction from white cabbage. Highest amounts of propionic and butyric acids were produced from inulin and barley fibres. In general, the fermentations with infant faeces gave a higher fraction of propionic acid and less acetic and butyric acid then faeces from adults. The GC-MS analyses revealed that monomers of the polysaccharides were detectable only for a short period early in the fermentation, and that the inoculum included significant amounts of amino acids, probably from dead bacteria. Some of the amino acids were consumed during the fermentation, and the relativ
