## 3 Results and Discussion
### Protein and Lipid Oxidation  
The sulfhydryl content was measured to evaluate the degree of protein oxidation in the samples, and the results are shown in Figure 1A. Compared with the control group (CT), the sulfhydryl content of samples prepared with nitrite (NT) significantly (\(p\) < 0.05) increased. This result indicated that the addition of sodium nitrite can inhibit the degree of protein oxidation in roasted lamb. This might be explained by the antioxidant activity of nitric oxide generated by the decomposition of nitrite during the processing of roasted lamb [2]. In addition, compared with the control sample, the sulfhydryl content of samples prepared with 30 min (PT30) and 45 min (PT45) plasma treatment increased by 3.85% and 2.45%, respectively, although there were not statistically significant (\(p\) > 0.05) differences. The results clearly showed that the plasma treatment did not aggravate the protein oxidation of roasted lamb in this study. In contrast, [PERSON] et al. [30] found that the plasma treatment for 60 s could exacerbate the protein oxidation of modified-package pork by the reactive oxygen species interacting with the protein. This difference may be caused by the different processing parameters, packing methods, and the meat types.  
\begin{table}
b  
b  
b  
\end{table}
Table 2: Changes in nitrite content (mg/kg) in roasted lamb.  
Malondialdehydedehyde (MDA), a secondary product of lipid oxidation, is usually determined by the TBARS analysis to evaluate the degree of lipid oxidation. The TBARS values are shown in Figure 1B. NT, PT15, PT30, and PT45 reduced the TBARS value by 69.35%, 62.34%, 60.12%, and 61.66% compared with CT, respectively. The result demonstrated that the degree of lipid oxidation in roasted lamb was inhibited by sodium nitrite and plasma treatment, and the inhibition effect of plasma treatment on lipid oxidation reached values from 86.69% to 89.89% compared with the sodium nitrite treatment. Previous studies have found that the nitrite can inhibit lipid oxidation in cured meat products such as ground ham [4; 18; 28]. It is well known that the initiation of lipid oxidation is inhibited by the reaction of nitrite and oxygen species, and the lipid oxidation is terminated by the reaction of nitric oxide and lipid peroxyl radicals [28]. Generally, the reactive oxygen species (particularly the free radicals) from plasma can interact with lipids in the plasma-treated product and initiate the oxidation [31]. It has been reported that the plasma treatment increased the TBARS value in modified-package pork by promoting lipid oxidation [30]. The difference in the result from that of our study can be explained by the fact that the oxygen in the package promoted the formation of ozone and accelerated lipid oxidation. However, some studies have demonstrated that plasma treatment had no effect on the lipid oxidation of meat batter or canned ground ham [16; 32]. The differences in these results from our study could be due to the difference in the meat product type and the composition of gas used for generating plasma in these studies. [PERSON] et al. [33] reported that the TBARS value of bacon treated by helium-based plasma showed no significant difference from that of bacon treated by helium/oxygen-mixture-based plasma. However, the atmosphere was used to generate plasma in our study. Previous studies also reported that the type and content of reactive species-initiated lipid oxidation can be affected by the composition of gas in plasma [11; 31].