The Mechanism of Pectin-Mediated Thiamethoxam and Clothianidin Residues on Eggplant Peel and Enhanced Detection via Pectinase-Assisted Extraction

Matrix binding poses a challenge to accurate pesticide residue detection in fruits and vegetables. This study investigated the distribution, binding status, and detection accuracy of neonicotinoid insecticides thiamethoxam (TMX) and clothianidin (CLO) in eggplant. To address the limitations posed by matrix binding, a pectinase-assisted extraction method was developed, which significantly enhanced the detectable levels of pesticides compared to the standard method and cellulase-assisted extraction. In situ Raman mapping and scanning electron microscopy revealed a strong correlation between the pectin distribution and the pesticide residues observed near the epidermal surface. Spectroscopic, nuclear magnetic resonance, and computational chemistry analyses demonstrated that TMX formed covalent bonds with pectin, while CLO interacted through hydrogen bonding. Notably, thermal processing promoted the formation of amide bonds, reducing detectable TMX levels. In summary, the optimized pectinase-assisted extraction method increased detectable TMX and CLO levels in positive samples by 25–40%, providing an effective approach for overcoming matrix binding effects.