The consequences of fruit and vegetable fibre fermentation on their binding capacity for MeIQx and the effects of soluble fibre sources on the binding affinity of wheat bran preparations

Fruits and vegetables provide dietary fibre some of which ispartly soluble in the upper gut; in the colon it is highly fermentable.Using alcohol-insoluble residues prepared from a range of fruitsand vegetables the effects of fermentation on the changes incomposition and binding capacity have been assessed for thehydrophobic mutagen 2-amino-3,8-dimethylimidazo[4,5-f]lquinoxaline(MeIQx). Fermentation was extensive and resulted in destructionof most of the pectic polysaccharides. Of the unfermented vegetablefibre only cabbage had a measurable hydrophobic binding capacity.The binding capacities of unfermented apple, carrot and sugarbeet were negligible. After fermentation, binding capacities,(per mg of fermented residue), increased. Although fermentedcabbage was found to have the highest capacity of the fruitand vegetable fibres this remained less than the least effectiveof unfermented wheat bran samples which had a relatively highaffinity for MeIQx. Mucin inhibited the binding of MeIQx towheat bran fibre but apple fibre did not The results show thatthe contribution of fruit and vegetable fibre to a hydrophobicbinding matrix in the colon is insignificant and the suggestedharmful effect of fruit and vegetable fibre, maintaining hydrophobicmutagens in solution, can be prevented by the presence of wheatbran fibre.