Degradation of rye arabinoxylans in the large intestine of pigs

Four types of rye bread (based on whole rye, pericarp/testa, aleurone or endosperm) differing in arabinoxylan (AX) structure were fed to pigs. Collected intestinal material was extracted with cold water and 4 M potassium hydroxide, and the AX were characterised by methylation analyses. The endosperm AX were extensively and readily degraded in the caecum (0.78), whereas pericarp/testa AX were undegraded in the intestinal tract of pigs. Aleurone AX were also degraded to a large extent (faecal digestibility 0.73) but at a slower rate, and, in agreement, structural modification of aleurone AX also took place beyond the proximal colon. The differences in AX degradability correlated well with differences in water and alkali extractability and differences in structural characteristics of the AX. Endosperm AX were thus characterised by a large content of water-extractable AX and pericarp/testa AX by a very high degree of (mono- and double-) xylose substitution. In contrast, aleurone AX were characterised by the presence of an alkali-extractable AX with a very low degree of substitution, which precipitated upon dialysis of the alkali extract. The faecal xylose substitution patterns were similar irrespective of diet. The study thus showed that the structural characteristics of a dietary fibre component influenced dietary fibre degradation in pigs, which may hold important implications for the colonic health in monogastrics. © 1999 Society of Chemical Industry