Effects of Dietary Fibre and Probiotics on Hindgut Fermentation in Healthy Rats and in Rats with Dextran Sulphate Sodium-Induced Colitis and Colon Cancer
Sammanfattning: The importance of colonic fermentation has been realised during recent years as it has been found to be associated with colonic health and thus the overall health of the individual. The fermentation of dietary fibre and the addition of probiotics can have positive effects on the luminal environment and the colonic microbiota. Short-chain fatty acids, formed by the fermentation of dietary fibre, have also been found to have health-promoting effects, especially butyric acid has attracted much interest in relation to colonic health. This thesis describes investigations of hindgut fermentation in rat experimental models during normal and inflammatory conditions. Different cereals and blueberry husks were used alone or together with probiotics to study their effect on fermentation, and also their potential influence on the inflammatory process. Dietary fibre in blueberry husks was found to be very resistant to hindgut fermentation and this, together with the high excretion of fat and protein, contributed to a high faecal bulk. Blueberry husks yielded a high caecal proportion of acetic acid compared with other fibre materials and the fibre-free diet using the same rat model. Lower bacterial counts indicated that blueberry husks also have antimicrobial activity. The addition of probiotics resulted in lower amounts of carboxylic acids (CA) in the caecum and higher amounts in serum. Bifidobacterium spp. were able to lower the ammonia level in the serum, regardless of diet. A diet containing malt yielded higher levels of butyric acid in the hindgut and in the portal blood, where higher levels of propionic acid were also found, compared with diets containing whole-grain barley and brewer’s spent grain. The bifidobacteria counts were lower with malt than the other two barley fractions. The addition of Lactobacillus rhamnosus 271 resulted in higher proportions of butyric acid and higher levels of ammonia. The highest levels of butyric acid were found when L. rhamnosus 271 was given together with whole-grain barley. Rye bran, blueberry husks and probiotics all reduced the degree of inflammation in rats with dextran sulphate sodium (DSS)-induced colitis, as evidenced by the lower disease activity index (DAI) and levels of inflammatory markers. The levels of CA in the distal colon were higher in rats given rye bran than in those given blueberry husks, indicating that the fermentation of rye bran was slower. The addition of probiotics to the rye bran diet shifted the site of fermentation to the caecum. Supplementing the blueberry husks with probiotics changed the pattern of CA in the group given blueberry husks; reducing the proportion of acetic acid and increasing that of propionic acid. The caecal counts of Enterobacteriaceae were also reduced in the groups given diets containing fibre and probiotics, and a positive correlation was found between Enterobacteriaceae and the DAI, while the DAI was negatively correlated with several CA, including butyric acid. Only rye bran increased the caecal counts of lactobacilli, while the addition of probiotics to blueberry husks increased the lactobacilli caecal counts compared with blueberry husks alone. Blueberry husks and, to some extent, the combination of oat bran and blueberry husks, had the ability to ameliorate the inflammatory response, as evidenced by the lower DAI, lower numbers of colon wounds, and lower levels of haptoglobin and IL-18. Oat bran and the combination of oat bran and blueberry husks yielded larger caecal pool sizes and distal levels of CA than blueberry husks alone. Adding probiotics to blueberry husks resulted in higher distal levels of butyric acid. Blueberry husks reduced the Enterobacteriaceae counts, while the addition of probiotics to all fibre diets yielded higher levels of lactobacilli. In conclusion, blueberry husks, rye bran and the combination of oat bran and blueberry husks were able to attenuate the DSS-induced colonic inflammation, although blueberry husks seemed to have the strongest attenuating effect, which could be due to its specific dietary fibre composition or possibly the polyphenol content. The addition of probiotics improved the effects in the hindgut.
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