In vitro fermentation of mixtures of indigestible carbohydrates by the human faecal bacteria
Aim of this thesis was to evaluate mixtures of indigestible carbohydrates in vitro to predict their effects on gut function. In this study, I investigate the effect of combining carbohydrates with different fermentative properties and their interactive influences, reflected in the end products from in vitro fermentation. The study focused on the rate of fermentation and fermentability of such mixtures and the SCFA produced to gain an index of the likely site of fermentation in the colon. The main aim of the thesis was to produce a mixture of carbohydrates which would delay but preserve butyrate production from rapidly fermenting carbohydrates such as raftilose. This was achieved in several mixtures but mostly those containing raftilose and ispaghula. In general, mixtures of carbohydrates were fermented more slowly than raftilose alone. Overall, ispaghula was the most effective in slowing the rate of fermentation compared with pectin or gums. Mixing raftilose with ispaghula or guar gum gave the best preservation of n-butyrate and propionate production. The rate of n-butyrate production was less rapid in mixed cultures of three carbohydrates (raftilose, ispaghula and pectin) than cultures of 100mg raftilose but production of n-butyrate was preserved. In summary, ispaghula and raftilose in two-carbohydrate mixtures and ispaghula, pectin and raftilose in three-carbohydrate mixtures delayed the release of butyrate with no loss in butyrate production and may move butyrate further round the colon, at the same time reducing the potential adverse effects of raftilose. Moreover, the addition of pectin (or guar gum) may add the therapeutic effect of delaying nutrient absorption in the small intestine was well. These studies have identified at least two mixtures (raftilose & ispaghula; raftilose, ispaghula & pectin) worthy of study in more detail in man.