Abstract:The binding characteristics of three water-insoluble rice proteins(globulin, glutenin, prolamin) and Pb2+ were studied from the perspective of kinetics and thermodynamics to explore the binding behaviors of different rice protein components and heavy metal lead ion(Pb2+). The result showed that Pb2+ was rapidly bound to each insoluble rice protein, and the binding equilibrium was reached within 30 min. The prolamin showed the highest binding capacity with a binding adsorption quantity(q) of 20.54 mg/g. The binding of Pb2+ to rice proteins was consistent with the quasi-second-order kinetic model, and the Langmuir equation(R2=0.980~0.995) had greater fitting effect than that of the Freundlich equation(R2=0.847~0.987). The result indicated the interaction between protein subunits and Pb2+ was mainly by chemical absorptions. The thermodynamic parameters, i.e., ΔS°>0, ΔH°>0 and ΔG°<0, indicated the spontaneous, entropy-driven and endothermic binding reaction. X-ray photoelectron spectroscopy(XPS) showed that the characteristic peak intensity of N1s and S2p was significantly decreased after binding (P< 0.05), suggesting that the major binding sites of prolamin for Pb2+ were nitrogen- and sulfur-containing groups. Scanning electron microscopy (SEM) displayed that the prolamin structures aggregated and formed a compact cloddy structure after binding to Pb2+, which further verified the binding of Pb2+ to rice prolamin.
