Fermentation of dietary fibre in the intestinal tract of rats — a comparison of flours with different extraction rates from six cereals

The fermentation of dietary fibre in wheat, rye, barley, sorghum, rice and maize was investigated in balance experiments with rats. Two different extraction rates, 100% and approximately 65%, were investigated for each cereal grain. In the case of maize, whole maize, and dehulled maize that had been ground and sieved so that it contained mainly endosperm, were investigated. Except for sorghum, dietary fibre in low-extraction flours was fermented to a greater extent than that in whole-grain flours. The sugar monomer compositions of the fibres at low and high extraction rates were similar for wheat and rye, but their susceptibilities to fermentation by bacterial enzymes were quite different. This indicates that a high proportion of soluble fibre and a low content of lignin improves the fermentability of the fibre. Further, barley, rice and sorghum fibre in refined flours, all of which consisted mainly of non-lignified glucans, were fermented more extensively when the proportion of soluble fibre was high. Addition of cellulose to diets containing wheat flour did not change the susceptibility of the wheat fibre to bacterial fermentation. Starch was demonstrated in faeces from rats fed wheat, sorghum and whole-grain rye flours. This starch represented 17–61 % of the total faecal glucan, but constituted less than 1% of the starch intake.