Carboxylic acids in the hindgut of rats fed highly soluble inulin and Bifidobacterium lactis (Bb-12), Lactobacillus salivarius (UCC500) or Lactobacillus rhamnosus (GG)

BACKGROUND: Propionic and butyric acids are important nutrients for the mucosal cells and may therefore increase the nutritional status and reduce the permeability of the colonic mucosa. These acids have also been suggested to counteract diseases in the colon, e.g. ulcerative colitis and colon cancer. Different substrates lead to different amounts and patterns of carboxylic acids (CAs). OBJECTIVE: To study the effect of probiotics on CA formation in the hindgut of rats given inulin. DESIGN: The rats were given inulin, marketed as highly soluble by the producer, together with the probiotic bacteria Bifidobacterium lactis (Bb-12), Lactobacillus salivarius (UCC500) or Lactobacillus rhamnosus (GG), or a mixture of all three. RESULTS: Rats fed inulin only had comparatively high proportions of propionic and butyric acids throughout the hindgut. When diets were supplemented with Bb-12 and UCC500, the caecal pool of CAs increased compared with inulin only. In the caecum the proportion of butyric acid generally decreased when the rats were fed probiotics. In the distal colon the proportion of propionic and butyric acid was lower, while that of lactic acid was generally higher. The caecal pH in rats fed GG and Bb-12 was lower than expected from the concentration of CAs. Further, rats fed GG had the lowest weight gain and highest caecal tissue weight. CONCLUSIONS: It is possible to modify the formation of CAs by combining inulin with probiotics. Different probiotics had different effects.