In vitro fermentation of polysaccharides of rye, wheat and oat brans and inulin by human faecal bacteria

The in vitro fermentabilities of rye, wheat and oat brans and of a commerci al fibre preparation, inulin, were compared. The brans were first digested enzymatically to remove starch and protein. The digested brans and inulin w ere then fermented with human faecal inoculum. The progress of fermentation was studied by following the consumption of carbohydrates and the producti on of short-chain fatty acids and gases. Inulin, a short fructose polymer, was consumed significantly faster than the more complex carbohydrates of ce real brans. Carbohydrates of oat bran (rich in beta-glucan) were consumed a t a higher rate than those of rye and wheat brans (rich in arabinoxylan). I n all brans, glucose was consumed faster than the other main sugars, arabin ose and xylose, and arabinose was degraded only slightly. The total product ion of short-chain fatty acids was slightly higher with oat bran than with rye and wheat brans and inulin. In the fermentation of inulin, relatively m ore butyric acid and less propionic acid were produced than in the fermenta tion of brans. The decrease in pH was also greater In the case of inulin. W heat bran led to a slightly slower gas formation than rye and oat brans. Fo rmation of gases was fastest and greatest in the case of inulin. In conclus ion, rye, wheat and oat brans were fermented in a rather similar way. Ferme ntation of the brans was different from that of inulin. Cereal brans might serve as a more balanced source of dietary fibre supplement than gas-produc ing, readily fermentable polysaccharides such as inulin. (C) 2000 Society o f Chemical Industry.