Oat Bran but Not a β-Glucan-Enriched Oat Fraction Enhances Butyrate Production in the Large Intestine of Pigs

Digestibility of polysaccharides and other macronutrients and the metabolic response of the microflora in the large intestine to a low dietary fiber wheat flour diet and three enriched diets with equal amounts of added dietary fiber (oat bran, a β-glucan-enriched oat fraction and insoluble oat residues) were studied in ileal-cannulated pigs. The digestibility of starch was high in the small intestine (98–100%). At this site of the gastrointestinal tract there was also a significant degradation of mixed linked β(1→3; 1→4)-D-glucan (β-glucan) (45–54%), whereas arabinoxylan was quantitatively recovered in ileal effluent. Type and amount of polysaccharides passing the ileal-cecal junction had little effect on the density of microorganism in the large intestine (~1010 viable counts/g digesta) but did have a high impact on the activity of the flora in colon as measured by the concentration of ATP in digesta. The relative proportion of butyrate in the short-chain fatty acids in the luminal contents of the large intestine was 6.6–8.4% when the low dietary fiber wheat flour diet was fed. However, when either oat bran or insoluble residues were included in the diet, the level was raised to 9.3–11.2%. No effect was seen after the addition of the β-glucan-enriched fraction. This study showed that arabinoxylan and not β-glucan in the cell walls of oat bran was responsible for the enhanced butyrate production of oat bran.