Removal of cadmium from rice proteins by soaking with hydrochloric acid or ethylene diamine tetraacetic disodium solutions

In this study, removal of cadmium (Cd²⁺) from rice proteins (RPs) by soaking with hydrochloric acid (HCl) or ethylene diamine tetraacetic disodium (EDTA-2Na) solutions was reported. For HCl-soaking, Cd²⁺ removal reached equilibrium within 30-min treatment, and the size of RPs particles and reaction temperature had negligible effects on the Cd²⁺ removal rate (R_Cd). However, extra washing of HCl-treated RPs by distilled water or acid solution can further enhance R_Cd effectively. The reaction pH had a profound effect on R_Cd, and the reduction of pH values from 5.5 to 4 can boost R_Cd from 16.4% to 92.3%. On the other hand, by increasing the concentration of EDTA-2Na from 10 μg/mL to 40 μg/mL at pH 7, R_Cd increased from 69.1% to 92.0%. However, the reduction of pH resulted in the formation of insoluble conjugates consisting of RPs, EDTA and Cd²⁺, therefore lowering R_Cd. Both of the two methods reduced the mineral content in RPs, but had no significant impact on their amino acid compositions. Furthermore, compared to the soaking by EDTA-2Na, acid treatment weakened the emulsifying and foaming capabilities of RPs to a greater extent.