Propionic and butyric acids, formed in the caecum of rats fed highly fermentable dietary fibre, are reflected in portal and aortic serum.

SCFA are important end products formed during colonic fermentation of dietary fibre (DF). It has been suggested that propionic and butyric acids affect metabolic parameters, low-grade systemic inflammation, insulin resistance and obesity. The aim of the present study was to investigate whether the various SCFA profiles observed after fermentation in the caecum of rats fed pectin, guar gum and fructo-oligosaccharides (FOS) were also represented in hepatic portal and aortic serum. The SCFA in serum were extracted using hollow fibre-supported liquid membrane extraction before GLC analysis. The concentrations of acetic, propionic and butyric acids in caecal content correlated well with those in portal serum (P< 0·001) for all the three diets. A weaker correlation was found for propionic and butyric acids between the caecal content and aortic serum (P< 0·05). Butyric acid concentration in caecal content was also reflected in the aortic serum (P= 0·019) of rats fed FOS. FOS gave rather low amounts of the SCFA, especially butyric acid, but caecal tissue weight was higher with FOS than with the other two diets. This may be explained by rapid fermentation and quick utilisation/absorption of the SCFA. The present study also showed that propionic acid was metabolised/utilised to a higher extent than butyric acid by colonocytes before reaching the liver. We conclude that the formation of propionic and butyric acids in the caecum is reflected by increased concentrations in the aortic blood. This approach may therefore simplify the evaluation and study of SCFA from DF in human subjects.

Malt in combination with Lactobacillus rhamnosus increases concentrations of butyric acid in the distal colon and serum in rats compared with other barley products but decreases viable counts of cecal bifidobacteria.

Several substances, including glutamine and propionic acid but in particular butyric acid, have been proposed to be important for colonic health. ß-Glucans lead to the formation of comparatively high amounts of butyric acid, and germinated barley foodstuff obtained from brewer's spent grain (BSG), containing high amounts of ß-glucans and glutamine, has been reported to reduce the inflammatory response in the colon of patients with ulcerative colitis. The present study examines how 3 barley products, whole grain barley, malt, and BSG, affect SCFA in the hindgut and serum of rats and whether the addition of Lactobacillus rhamnosus 271 to each of these diets would have further effects. Amino acids in plasma and the cecal composition of the microbiota were also analyzed. The butyric acid concentration in the distal colon and serum was higher in the malt groups than in the other groups as was the serum concentration of propionic acid. The concentrations of propionic and butyric acids were higher in the cecum and serum of rats given L. rhamnosus than in those not given this strain. The proportion of plasma glutamine and the cecal number of bifidobacteria were lower in the malt groups than in the other groups. L. rhamnosus decreased the number of cecal bifidobacteria, whereas plasma glutamine was unaffected. We conclude that malt together with L. rhamnosus 271 had greater effects on propionic and butyric acid concentrations in rats than the other barley products. This is interesting when developing food with effects on colonic health.

Short-chain fatty acid formation in the hindgut of rats fed native and fermented oat fibre concentrates.

The formation of SCFA in rats fed fermented oat fibre concentrates was compared with that of rats fed native oat fibre concentrate. The cultures used were lactic acid bacteria consisting of Lactobacillus bulgaricus and Streptococcus thermophilus (V2), the exopolysaccharide-producing strain Pediococcus damnosus 2.6 (Pd) and L. reuteri (Lr). The materials were incorporated into test diets yielding a concentration of indigestible carbohydrates of 80 g/kg (dry weight). Rats fed the V2-fermented fibre-concentrate diet yielded higher caecal and distal concentrations of acetic acid (P < 0.01) than rats fed the native fibre concentrate. All the fermented fibre concentrates resulted in a higher propionic acid concentration in the distal colon (P < 0.05), while rats fed Pd-fermented fibre concentrate resulted in lower concentration of butyric acid (P < 0.05, P < 0.01) in all parts of the hindgut as compared with rats fed the native fibre concentrates. Butyrate concentrations ranged between 5-11 micromol/g (distal colon) and 6-8 micromol/g (13 d faeces). Higher proportions of acetic acid (P < 0.05; P < 0.01) were observed in the caecum of rats fed the fermented fibre concentrates. Rats fed Pd- and Lr-fermented fibre concentrates produced higher proportions of propionic acid (P < 0.05; P < 0.01) in the caecum. Changes in SCFA formation in the caecum, distal colon and faeces of rats fed the fermented samples compared with the native sample indicate that these microbes probably survive in the hindgut and that modification of the microflora composition with fermented foods is possible. This may be important for the gastrointestinal flora balance in relation to colonic diseases.