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• Lactobacillus plantarum can degrade 81.28% of dimethoate in milk rapidly. • Enzyme is the main mechanism for Lactobacillus plantarum to degrade dimethoate. • Five degradation products of dimethoate were identified by UPLC-QTOF/MS. Bioremediation of pesticides in contaminated foodstuffs using probiotics has attracted great attention in recent years, but some intermediate products may have profound effects on the toxicity of treated food. Therefore, this work studied the degradation mechanism of dimethoate in milk by L. plantarum, and analyzed the toxicity of degradation products. The results showed that under the optimal conditions, L. plantarum can degrade 81.28% of dimethoate. Dimethoate had high binding affinities to phosphatase with the free energy of –16.67 kcal/mol, and amino acid residues, Gln375 and SER415 played important roles in the catalysis process. Five degradation products were identified using UPLC-QTOF/MS, and their toxicity was estimated using quantitative structure–activity relationship models. Some intermediate products were predicted to be toxic, which should not be ignored, but the overall toxicity of milk decreased after fermentation. Furthermore, the pH and titratable acidity of the fermented milk were 4.25 and 85 ◦T, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • The spontaneous binding behavior of CTC to casein was revealed for the first time. • Binding sites engaged in the formation of the casein-CTC complex were deciphered. • The complexation between casein and CTC inhibited the thermal degradation of CTC. Bovine casein was selected as a model protein to evaluate the impact of food matrix on the thermal degradation of antibiotics. Fluorescence quenching and isothermal titration calorimetry experiments revealed that chlortetracycline (CTC) could spontaneously bind to casein via hydrogen bonding and hydrophobic interactions. The amino acid residues forming the binding pocket were further identified using molecular docking, while saturation transfer difference NMR deciphered that the binding of CTC engages its -N(CH 3) 2 group. Moreover, the degradation behavior of free CTC versus that bound in casein-CTC complex was compared during thermal treatment. Compared with free CTC, a lower first-order rate constant was observed in the presence of casein. Removal of casein shortened the half-life of CTC by at least 48.1% at low concentrations. Elucidating that the formation of protein-antibiotic complexes alters the amenability of antibiotics to degradative reactions, which could help eliminate residual antibiotics and guarantee the safety of dairy products. [ABSTRACT FROM AUTHOR]