Interaction between Six Waxy Components in Summer Black Grapes (Vitis vinifera) and Mancozeb and Its Effect on the Residue of Mancozeb.

Mancozeb, an antifungal typically used for the growth of fruits, has the characteristic of non-internal absorption, and has a risk of binding to the waxy components of fruits. This work investigated the interaction of pesticide molecules with the waxy layer on the grape surface and their effects on pesticide residues in grapes. The study observed significant changes in the compositions of the waxy layer on the grape surface after soaking in a mancozeb standard solution. The six substances-oleanolic acid, ursolic acid, lupeol, octacosanol, hexacosanal, and γ-sitosterol-with discernible content differences were chosen for molecular docking. Docking results were further visualized by an independent gradient model based on Hirshfeld partition (IGMH). Hydrogen bonds and van der Waals forces were found between mancozeb and the six waxy components. Moreover, the negative matrix effects caused by the presence or absence of wax for the determination of mancozeb were different through the QuEChERS-HPLC-MS method. Compared with the residue of mancozeb in grapes (5.97 mg/kg), the deposition of mancozeb in grapes after dewaxing was significantly lower (1.12 mg/kg), which further supports that mancozeb may interact with the wax layer compositions. This work not only provides insights into the study of the interaction between pesticides and small molecules but also provides theoretical guidelines for the investigation of the removal of pesticide residues on the surface of fruits.

Electrolyzed water combined with ozone treatment for efficient removal of mancozeb residues from grapes.

Existing cleaning methods mainly focus on removing free-state pesticides. However, mancozeb can bind to the wax layer of grapes, forming bound-state residues that are difficult to remove. This study aims to develop an effective cleaning strategy to eliminate both free and bound mancozeb residues from grapes. Compared with the untreated mancozeb aqueous solution, the concentration of free mancozeb significantly decreased (p < 0.05) after treatment with ozonated water (OW), electrolyzed water (EW), and their combination (OW+EW) for 60 min. The combined treatment synergistically promoted mancozeb degradation, thus reducing its half-life to 38% and 75% of that observed when OW and EW were used alone, respectively. To investigate the effect of the waxy layer on mancozeb removal, oleanolic acid (OLA) was selected as a representative component. The binding effect of OLA limited the degradation of mancozeb in OW and EW, extending its half-life by 1.27 and 1.20 times, respectively. Density functional theory elucidated the mechanism by which the binding of OLA affects the degradation of mancozeb. Interestingly, the decomposition of mancozeb in OW + EW was almost unaffected by the introduction of OLA, indicating that the combined treatment could effectively remove bound-state mancozeb. The combined treatment was then successfully applied to remove mancozeb from grapes. After exposure to OW + EW for 10 min, the removal efficiency of mancozeb reached up to 80.61% with minimal risks of ethylene thiourea formation. There was no obvious change in the surface color of grapes after treatment. The findings provide valuable guidance for removing mancozeb from fresh fruits rich in waxy coatings.