The effect of fibre source and fermentation on the apparent hydrophobic binding properties of wheat bran preparations for the mutagen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx)

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Abstract
Preparations of dietary fibre have an ability to bind potentially toxic compounds in vitro, but it is unclear how the measured binding properties are a reflection of either the relative affinity of such compounds for fibre or the saturation binding capacity of the fibre. Cooking and processing of foods and fermentation activity in the colon can result in significant modification of the structure of the fibre matrix. Hence, binding properties measured in vitro may be significantly altered from those at the proposed site of fibre activity. Using cell wall material (CWM) prepared from three distinct wheat fibre sources, the effects of fermentation have been monitored and the consequences on the binding properties assessed. The CWM preparations were fermented for either 0, 6, 18 or 24 h in vitro, using a human faecal inoculum. The coarse bran CWM was also subjected to a simulated gastric treatment. Fermentation resulted in a loss of material from each CWM preparation, the loss being consistent with the bran source, and the maximum extent of fermentation was reached within 18 h. The in vitro binding of the mutagen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) to the unfermented and fermented fibre fractions showed fine bran CWM had a much higher affinity for MeIQx than coarse bran. A 6 h fermentation had little effect on the binding affinity to fine bran, but the affinity for coarse bran became similar to that of the fine bran. Further fermentation for 18 h or 24 h resulted in a further slight increase in the binding affinity for coarse and fine bran, but, more significantly, the binding capacity of each was increased. The binding properties of the beeswing bran were not significantly affected by fermentation. Wheat bran has the potential to bind hydrophobic mutagens in the diet and this potential can be enhanced after fermentation under colonic conditions.

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