*3.4. Effect of Cooking Methods on Residues of Amphenicols and Metabolites in Livestock and Poultry Meat*

In order to compare the effects of different cooking methods on the concentration changes of amphenicols and metabolites in livestock and poultry meat, each cooking endpoint was selected for analysis in this study (Figure 3). Among the three cooking methods, microwaving increased the concentration of the four drug residues in the meat matrices of livestock and poultry, while boiling and deep-frying had the opposite effect, and the removal effects of the two were also different. Figure 3 illustrates that the removal rates of CAP and FF in four types of livestock and poultry meat and of TAP in pork, beef and lamb by boiling were significantly higher than those in deep-frying (*p* < 0.05), but there was no significant difference between the two for TAP in chicken (*p* > 0.05). In terms of FFA, there was no significant difference between boiling and deep-frying in pork, beef

and chicken (*p* > 0.05), while the removal rate of boiling was lower than that of deepfrying in lamb (*p* < 0.05). These results have shown that different cooking methods have different effects on the removal of amphenicols and metabolites from livestock and poultry meat. Boiling showed the highest reduction effect on the drug residues in livestock and poultry meat matrices, followed by deep-frying, while microwaving caused an increase in drug residue concentrations. Based on the previous reports, we speculate that the reduction in drug residue concentrations in the matrices by boiling and deep-frying may be related to moisture loss, drug migration and degradation [11,23,24]. In addition, the overall removal rate of amphenicols and metabolites in livestock and poultry meat observed in this experiment was higher with boiling than with frying. The reason for this may be that, on the one hand, the heating rate of deep-frying is faster than that of boiling, less water is lost in the form of transfer in deep-frying than in boiling for the same degree of mass loss (Figure 2) and less of the drug is lost with it. On the other hand, deep-frying may create a hard crust on the surface of the meat, which, in turn, slows down the rate of drug loss with moisture [25].

**Figure 3.** The rate of change in residue concentrations of amphenicols and metabolites in livestock and poultry meat under different cooking methods. (**a**) CAP; (**b**) TAP; (**c**) FF; (**d**) FFA. Different lowercase letters represent significant differences (*p* < 0.05) in the reduction rate of the same drug in the same species of livestock and poultry meat under boiling (25 min) and deep-frying (5 min) treatments. The same lowercase letter indicates no significant difference (*p* > 0.05).
