*3.1. Homogeneity Analysis of Positive Simulated Samples*

Studies related to the effect of thermal processing on drug residues have shown significant differences in the percentage of thermal degradation of amphenicols in model solutions (water), spiked tissues and incurred samples, and their degradation products vary. To provide reliable information on the stability of residues of amphenicols for food safety risk assessments, Tian [14] suggested that incurred samples should be systematically implemented rather than spiked tissues to study the impact of cooking on drug residues. However, the subject of this experiment was livestock and poultry meat, and positive samples contaminated with amphenicols and metabolites from the market were difficult to collect. Furthermore, livestock and poultry animals bioaccumulate slowly, and it is also challenging to obtain contamination through controlled laboratory conditions. Therefore, in this study, positive mock samples could only be obtained by adding amphenicols and metabolites standards to negative livestock and poultry meat samples.

In order to ensure the consistency of the target compound concentrations in the meat blocks used for subsequent cooking, the homogeneity analysis of positive mock samples was carried out in this experiment, and the results are shown in Table 4. The one-way ANOVA showed *p* > 0.05 for the measured concentrations of amphenicols and metabolites in pork, beef, lamb and chicken blocks, indicating that the differences in drug concentrations between meat nuggets were insignificant. That is, the meat nuggets prepared by this experimental method had a good homogeneity and could meet the requirements for subsequent cooking.


**Table 4.** Homogeneity analysis of amphenicols and metabolites added to livestock and poultry meat blocks.

Positive simulated meat blocks of each matrix (pork, beef, lamb and chicken) were divided into three groups corresponding to the subsequent boiling, deep-frying and microwaving treatment groups. The three groups for pork were numbered P-1, P-2 and P-3, respectively. The three groups for beef were numbered B-1, B-2 and B-3, respectively. The three groups for lamb were numbered L-1, L-2 and L-3. The three groups for chicken were numbered C-1, C-2 and C-3. No. 1, No. 2 and No. 3 were the three meat blocks randomly selected from each group.

#### *3.2. Processing Quality Loss of Livestock and Poultry Meat*

The effects of boiling, deep-frying and microwave processing on the quality loss of livestock and poultry meat are shown in Figure 2. The mass loss of livestock and poultry meat during boiling showed an overall trend of rising and then leveling off with time. After 20 min of boiling, the quality of pork, beef, lamb and chicken remained stable (*p* > 0.05). During deep-frying and microwave processing, livestock and poultry meat quality loss continued to increase over time (*p* < 0.05). The quality losses of pork, beef, lamb and chicken were 39.89%, 44.95%, 42.61% and 32.60% and 39.98%, 47.34%, 44.76% and 36.91% at 25 min of boiling and 5 min of deep-frying, respectively, and the degree of loss was similar for both. At 1.25 min of microwaving, the quality loss of the four livestock and poultry meat species reached 29.82%, 50.19%, 50.26% and 45.41%, respectively. Compared with boiling and deep-frying, the quality loss rate was faster in microwaves. The reason is that microwaves can heat the whole material simultaneously, which results in a violent heating process, rapid temperature rise and faster water evaporation, thus causing the most severe quality loss in a short time. The determination of the quality loss index should facilitate the understanding of the effect of subsequent cooking on the concentration of drug residues in livestock and poultry meat.

**Figure 2.** Processing quality loss of livestock and poultry meat. (**a**) Boiling; (**b**) Deep-frying; (**c**) Microwaving.
