COMPARATIVE-STUDY OF THE FERMENTATIVE CHARACTERISTICS OF INULIN AND DIFFERENT TYPES OF FIBER IN RATS INOCULATED WITH A HUMAN WHOLE FECAL FLORA

It is known that the physico-chemical characteristics of fibre modify their fermentation characteristics in the colon, Previously we showed the varying effects of inulin and different types of fibre on the hepa tic and intestinal xenobiotic-metabolizing enzymes (XME) in initially germ-free rats inoculated with a human, methanogenic, whole-faecal flo ra (Roland et al, 1994), The aim of the present work was to assess whe ther or not these effects could be related to differences in productio n of fermentation metabolites (gases excreted is vivo acid caecal meta bolites) due to the different compositions of fibre, The different typ es of fibres were analysed with regard to their solubility and their c omposition of neutral monomers and uronic acids, Inulin was totally so luble, carrot (Daucus carota), cocoa (Theobroma cacao) and wheat bran were partially soluble;pea (Pisum sativum) and oat were nearly totally insoluble, Uronic acids were found mostly in carrot and cocoa fibre, Glucose was present as the main neutral monomer in each fibre type, Xy lose was found also in wheat bran, pea and oat fibres, and arabinose w as found in wheat bran, Inulin consumption led to high levels of H-2 p roduction but no CH4 production, to a 4-fold greater caecal concentrat ion of butyrate than with the other fibres and to a decrease in caecal pH. Conversely, rats fed on carrot or cocoa fibre produced a large am ount of CH4 but no H-2 and generated a different profile of short-chai n fatty acids (SCFA), The lowest amounts of gases and SCFA were found in rats fed on wheat bran, pea and oat fibre, We observed a relationsh ip between the caecal concentration of SCFA and the activity of hepati c glutathione-S-transferase (EC 2.5.1.18) but no direct link was shown between the other XME and the fermentation profile.