ADSORPTION OF A HYDROPHOBIC MUTAGEN TO DIETARY FIBER FROM TARO (COLOCASIA-ESCULENTA), AN IMPORTANT FOOD PLANT OF THE SOUTH-PACIFIC

The incidence of colorectal cancer is lower in Polynesian populations of the South Pacific than in European populations. This difference in incidence of the disease may be, at least partly, related to diet. Dietary fiber is believed to protect against colorectal cancer, and one of the ways it may act is by adsorbing mutagens that are carcinogenic. Very little is known about the chemical composition or the ability to adsorb mutagens of these dietary fibers from South Pacific food plants. In contrast to European food plants, which are mostly dicotyledons, South Pacific food plants are mainly monocotyledons. We isolated cell walls (dietary fiber) from the three edible parts of taro (Colocasia esculenta), which is a monocotyledon and a major South Pacific food plant. The ability of these three unlignified cell-wall preparations to adsorb the hydrophobic environmental mutagen 1,8-dinitropyrene was studied. The greatest adsorption occurred with walls from leaf blade, followed by petiole and corm walls, although the differences were not major. The amount of adsorption was intermediate between the low adsorption previously found with unlignified dicotyledon walls (from the flesh of potato tubers and immature cabbage leaves) and the much higher adsorption found with unlignified walls from monocotyledons of the grass and cereal family (Poaceae) (from leaves of seedling Italian ryegrass). These data are consistent with the monosaccharide compositions of the taro wall preparations, which were more similar to those of unlignified walls of dicotyledons than to unlignified walls of the Poaceae. These findings are consistent with the hypothesis that the composition of the dietary fiber determines its adsorptive properties and that there may be important differences between the major dietary fibers of South Pacific and European food plants.