THE ADSORPTION OF HETEROCYCLIC AROMATIC-AMINES BY MODEL DIETARY-FIBERS WITH CONTRASTING COMPOSITIONS

It is often recommended that consumption of dietary fibre should be in creased to protect against colorectal cancer. However, although more t han 95% of dietary fibre is contributed by whole plant cell walls, ver y little experimental work has been done using whole plant cell walls. These may protect by adsorbing carcinogens, thus lowering their effec tive concentration in the alimentary tract, and by carrying the carcin ogens out of the body in the faeces. However, plant cell walls vary wi dely in their composition and physical properties, and not all cell wa lls will necessarily have protective properties. We therefore isolated 4 plant cell-wall preparations with contrasting compositions as model s of the types of cell walls that occur in the diet, We investigated t he abilities of these preparations to adsorb in vitro 6 heterocyclic a romatic amines (HAAs). HAAs occur in the human diet and several are co lon carcinogens, at least in rats. We found that the ability of the HA As to adsorb to the plant cell walls increased with increasing hydroph obicity of the HAA, measured as the calculated logarithm of the partit ion coefficient between I-octanol and water (C logP). A cell-wall prep aration containing mainly the walls of parenchyma cells (the most comm on cell type in food plants) had only poor adsorptive ability. A cell- wall preparation from commercial cork had the best adsorptive ability. This preparation was the most hydrophobic of those examined because t he cell walls contained the polymer, suberin, together with associated waxes. The preparation modelled suberized cell walls which occur in t he diet, for example in potato skins. The other two cell-wall preparat ions contained another hydrophobic polymer, lignin, and had intermedia te adsorptive abilities which were not significantly different from on e another. These preparations modelled lignified cell walls which occu r in the diet, for example in wheat bran. Our results indicate that su berized and lignified cell walls may be important in protecting agains t colorectal cancer.