Cadmium binding capacity of cocoa and isolated total dietary fibre (TDF) was investigated in vitro under simulated physiological pH conditions. The effect of Cd2+ retention on the bioavailability of essential endogenous minerals was also studied. The sample was mixed with buffered Cd2+ solution and, after equilibration, the residue was separated for quantitative measurement of soluble Cd2+ in the supernatant. Cocoa exhibited a high affinity for Cd2+ in solution. The amount of bound Cd2+ rose with increasing metal concentration and pH. TDF was the major fraction responsible for binding of Cd2+ by cocoa. Phytate was probably another important cause of the decrease of Cd2+ solubility. The addition of various concentrations of Cd2+ to cocoa and TDF was shown to affect the solubility of endogenous minerals. When Cd2+ was bound by TDF there was a marked increase in the availability of endogenous Fe, Zn, Ca and Mg, specially at duodenal pH conditions.
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Valiente et al. (1996) studied this question.