Extraction of Pb(II) from wheat samples via dual-frequency ultrasound-assisted enzymatic digestion and the mechanisms of its interactions with wheat proteins

A novel dual-frequency ultrasound-assisted enzymatic digestion (DUED) technique was used to extract Pb(II) from certified reference materials (CRMs) of wheat flour. Following this, the interactions of Pb(II) with wheat proteins were investigated to provide evidence for the selection of enzyme species. The results showed that the simultaneous use of α-amylase and flavourzyme resulted in the recovery of 97.9% of Pb(II) in 6 min under a 40 kHz ultrasonic bath combined with a 20 kHz ultrasonic probe. The exopeptidase activity of the flavourzyme was found to be the main contributor to the extraction of Pb(II) from the CRMs. Additionally, the proposed method exhibited a low detection limit (8.2 ng/g) and high recoveries of real samples (93.4%-112.2%) with RSD less than 7.33%. Furthermore, the oxygen-containing groups of wheat proteins, the nitrogen-containing groups of albumins and globulins, and the sulfur-containing groups of gliadins and glutenins were found to offer coordination sites for Pb(II).