Degradation of rye arabinoxylans in the large intestine of pigs

Four types of rye bread (based on whole rye, pericarp/testa, aleurone or en dosperm) differing in arabinoxylan (PLY) structure were fed to pigs. Collec ted intestinal material was extracted with cold water and 4 M potassium hyd roxide, and the AX were characterised by methylation analyses. The endosper m AX were extensively and readily degraded in the caecum (0.78), whereas pe ricarp/testa AX were undegraded in the intestinal tract of pigs. Aleurone A X were also degraded to a large extent (faecal digestibility 0.73) but at a slower rate, and, in agreement, structural modification of aleurone AX als o took place beyond the proximal colon. The differences in AX degradability correlated well with differences in water and alkali extractability and di fferences in structural characteristics of the AX. Endosperm AX were thus c haracterised by a large content of water-extractable AX and pericarp/testa AX by a very high degree of (mono- and double-) xylose substitution. In con trast, aleurone AX were characterised by the presence of an alkali-extracta ble AX with a very low degree of substitution, which precipitated upon dial ysis of the alkali extract. The faecal xylose substitution patterns were si milar irrespective of diet. The study thus showed that the structural chara cteristics of a dietary fibre component influenced dietary fibre degradatio n in pigs, which may hold important implications for the colonic health in monogastrics. (C) 1999 Society of Chemical Industry.