In vitro fermentation of rye carbohydrates including arabinoxylans of different structure

Freeze-dried ileal effluent from cannulated pigs fed rye bread diets based on either whole rye or one of three rye milling fractions enriched in peric arp/testa, aleurone and endosperm was incubated in an in vitro fermentation system with faecal inocula from pigs fed a whole grain rye diet. Three and 48 hours of in vitro degradation of arabinoxylans were comparable to the c aecal and faecal degradation respectively. The productions of short-chain f atty acids were highest from the ileum samples of the diets high in ferment able carbohydrates (whole rye, aleurone and endosperm). However, fermentati on of the pericarp/testa ileum sample produced half the amount of short-cha in fatty acids resulting from the other ileum samples despite the fact that the pericarp/testa carbohydrates (CHO) were not fermented at all. Treating the pericarp/testa with alkali prior to the incubation increased fermentab ility considerably (from 0 to 49% of total arabinoxylans) and suggested tha t, at least in Lignified tissue, alkali-labile cross-links were more import ant determinants of arabinoxylan (AX) degradability than AX structure itsel f. Oxidative delignification of the pericarp/testa heal effluent increased fermentability too, but to a much lower degree, which indicates that the ty pe and extent of links between polymers and lignin rather than the amount o f lignin are important in determining degradability. (C) 2000 Society of Ch emical Industry.