Characterization of binding behaviors of Cd2+ to rice proteins

Abstract

In this paper, for the first time the binding behavior of cadmium (Cd²⁺) to rice proteins (RPs) was studied. The results showed that the equilibrium of binding was reached within 30 min at 303 K with a maximum binding amount (q) of 15.26 mg/g, and the pH was an important factor positively influencing q. At both 308 K and 313 K, the binding of Cd²⁺ to RPs belonged to spontaneous, endothermic interactions with high-affinity, assigned to a multidentate coordination. Except for acetate, all the investigated competing coordination agents, such as edetate, pyrophosphate and citrate, showed inhibitory effects on RPs-Cd²⁺ binding, and edetate seemed to be the most effective one. At pH 6.5, calcium, copper and zinc began to restrict RPs-Cd²⁺ binding when the metal ion concentration reached 500 mg/kg, and the decreasing of pH would strengthen the inhibitory effects of the investigated metal ions including ferric ions.

Keywords: Binding characteristics; Cadmium; Coordination competition; Rice protein.