The effect of pH, time and dietary source of cadmium on the bioaccessibility and adsorption of cadmium to/from lettuce (Lactuca sativa L. cv. Ostinata).

ABSTRACT

This study evaluated the influence of three variables in the effectiveness of an in vitro digestion protocol used to determine bioaccessibility of cadmium from the diet. The percentage of solubilized metal was measured in relation to digestion time, pH of each digestion phase and the dietary source of the metal in the diet. Because it would be convenient to add the metal to the diet before digestion instead of growing contaminated vegetables, the importance of metal incorporation in the plant in comparison to amendment through foliar spraying was also studied. From our results we conclude that the dietary source of metal in the protocols tested doesn't seem to be a significant factor when comparing the lettuce sprayed with cadmium with the lettuce that had cadmium incorporated in it, although the difference was barely significant (P=0.057). Time affects the digestion in different ways depending on the dietary source of cadmium. pH is a relevant factor in both intestinal and gastric phases and should be taken into consideration when analyzing the results from in vitro digestions. Since the intestinal phase in our experiments decreased the amount of cadmium solubilized during the digestion, we investigated the effect of pH on the adsorption of this metal to lettuce and found that there is an increased binding of cadmium at pH values above 3. Therefore we suggest that part of the reduction in bioaccessibility following intestinal digestion could be explained by an increase in adsorption of metal to the plant material at higher pH values.