Mechanochemical synthesis of cysteine-gum acacia intermolecular complex for multiple metal(loid) sequestration from herbal extracts.

The ubiquitous heavy metal(loid)s (HMs) contamination has triggered great concern about food safety, while sequestration and separation of trace HMs from herbal extracts still calls for appropriate sorbent materials. In this work, gum acacia was modified by cysteine to form a cysteine-acacia intermolecular complex (Cys-GA complex) via facile mechanochemical synthesis, aiming at capturing multiple HMs simultaneously. Preliminary screening confirms the superiority of Cys-CA complex for both cationic and anionic HMs, and determines an optimum Cys/GA mass ratio of 9:1 to achieve high removal capacities for Pb(II) (938 mg g), Cd(II) (834 mg g), As(V) (496 mg g), and Cr(VI) (647 mg g) in simulated aqueous solution. The analysis on HMs-exhausted Cys-GA complex indicates that Pb(II), As(V), and Cr(VI) tend to be removed through chelation, electrostatic attraction, and reduction, while Cd(II) can only be chelated or adsorbed by electrostatic interaction. The batch experiments on commercial herbal (e.g. Panax ginseng, Glycine max, Sophora flavescens, Gardenia jasminoides, Cyclocarya paliurus, and Bamboo leaf) extracts indicate that Cys-GA complex can reduce HMs concentration to attain acceptable level that comply with International Organization for Standardization, with negligible negative effect on its active ingredients. This work provides a practical and convenient strategy to purify HMs-contaminated foods without introducing secondary pollution.