Comparison of the Binding Ability to Cadmium between Rice Protein and Rice Dreg Protein

Objective:To compare the binding ability to cadmium of rice protein and rice dreg protein,and investigate the binding mechanism of protein to cadmium. Methods:The binding ability of proteins was compared by the binding amounts of two proteins to cadmium and the degree of removing cadmium bounded to protein. The size analyzer,circular dichroism spectrometer(CD),infrared spectrometer(FTIR),scanning electron microscope(SEM)and X-ray photoelectron spectroscopy(XPS)were used to analyze the binding mechanism of protein to cadmium. The importance of carboxyl and sulfhydryl groups of proteins to cadmium binding was verified by the cadmium binding test after masking carboxyl and sulfhydryl groups of proteins.Results:The maximum binding amount of rice dreg protein to cadmium was 12.08 mg/g,and the removal rate reached the maximum after 120 min. The maximum binding amount of rice protein to cadmium was 8.85 mg/g,and the combined cadmium was removed after 60 min. After masking the carboxyl group of protein,the binding amount of cadmium to both proteins decreased by 18% compared with before masking. After oxidation of sulfhydryl group,the binding amount of rice protein and rice dreg protein to cadmium decreased by 40% and 50%,respectively,compared with that before oxidation of sulfhydryl group. The SEM morphology observed that protein aggregated after binding to cadmium. Conclusion:Compared with rice protein,rice dreg protein had strong binding ability to cadmium. In addition,the binding of the two proteins to cadmium was not only a simple physical adsorption,but also the sulfhydryl and carboxyl groups in the protein played an important role in the binding of cadmium.