Efficient and safe removal of free and casein-bound oxytetracycline from milk via pulsed electric field.

Oxytetracycline (OTC) residues in milk spontaneously bind to casein, forming casein-OTC complexes that complicate their removal. This study assessed the degradation effect of pulsed electric field (PEF) treatment on OTC, with a particular focus on its protein-bound form. Casein-bound OTC was successfully prepared, and the effectiveness of PEF in removing casein-bound antibiotics was confirmed using DESI-MSI technology. Under optimal treatment conditions, the degradation rates of OTC in casein-free whey (86.30 % - 93.43 %) and milk (82.47 % - 90.31 %) showed no significant difference, further confirming that the removal efficacy of PEF on OTC was unaffected by casein binding. The degradation of OTC in both matrices followed the Hülsheger model. Four major degradation products were identified, involving three distinct pathways: epimerization, demethylation, and deamidation. Furthermore, cytotoxicity assays demonstrated that PEF treatment significantly reduced the overall toxicity of OTC in milk. This study provides an effective and safe strategy for removing OTC residues from milk.