Structural interplay and macroscopic aggregation of rice albumins after binding with heavy metal ions

Contamination of cereal grains by heavy metals is becoming a serious threat to human health, especially in the central regions of China. Herein, we report drastic changes in the supramolecular nanostructures of rice albumins (RAs) after binding with Cu(II), Cd(II), and Pb(II). Atomic force microscopy and scanning electron microscopy revealed that Cu(II) initiated an immediate precipitation of RAs, whereas Cd(II) and Pb(II) promoted the formation of core-satellite structures with a core of multiple protein particles surrounded by satellite particulates. Fluorescence and isothermal titration calorimetry studies revealed an entropy-driven, spontaneous behavior of the binding. Consequently, remarkable helix-sheet transitions of RAs were triggered and macroscopic precipitation occurred due to hydrophobic attraction. Our results may help to understand the binding between heavy metals and cereal ingredients from a hydrocolloid perspective to eventually develop detection and removal strategies to combat heavy metal contamination.