## 3 Result and Discussion
### Changes in the Composition of Volatile Flavor Compounds in Bacon  
As shown in Figure 1A, the reproducibility of parallel samples was analyzed via PCA, yielding a total score of 99.52%, which indicated that the model had a good ability to predict volatile compounds in bacon samples during different stages of LTS. The E-nose radar map (Figure 1B) illustrates the changes in the volatile flavor characteristics of Hunan bacon based on the signal values of 10 probes. Among them, the WSS, W1S, W2W, and W1W sensors were mainly sensitive to bacon samples and corresponded to nitrogen oxides; alkanes and aromatic compounds; organic sulfides; and sulfides, respectively, suggesting that bacon samples may contain high levels of compounds such as aldehydes, ketones, alkanes, and sulfides. E-noses have been widely used for the evaluation of food quality because they are rapid, sensitive, and nondestructive. This is analogous to previous findings that different types of wood-smoked bacon are equally susceptible to W2W, WSS, W2S, W1W, and W1S sensors and can be effectively distinguished from them [PERSON] et al. (2018).  
E-nose analysis revealed significant changes in flavor during the LTS of bacon and that the type, content, and balance of volatile flavor compounds played a crucial role in impacting the flavor. A total of 42 volatile flavor compounds were identified in the bacon sample via SPME-GC-MS: 13 ketones, 11 hydrocarbons, 7 aldehydes, 5 acids, 4 esters, 1 furan, and 1 nitride (Table S1). Ketones were the most abundant (67.9%), followed by aldehydes (14.4%). Previous studies have shown that ketones and aldehydes are produced during amino acid breakdown and fat oxidation [PERSON] et al. (2018). The content of the majority of volatile compounds underwent a significant change during LTS, particularly 3-methyl-1,2-cyclopentone, 3-methylcyclopent-2-en-1-one, and 2,3-dimethyl-2-cyclopentene-1-one, with the ketones exhibiting flavors that are commonly perceived as burnt and sweet. This indicates that low-temperature liquid smoking may enhance the flavor of bacon.  
\begin{table}
\begin{tabular}{l l l l l l l} \hline \hline \multirow{2}{*}{**Item**} & \multicolumn{3}{c}{**Human Bacon Low-Temperature Liquid Smoking Time (Days)**} & \multirow{2}{*}{\begin{tabular}{c} **Liquid Smoking Time (Days)** \\ **0** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **10** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **10** \\ \end{tabular} } \\  & & & & & & \\ \hline L* & 48.3 \(\pm\) 1.12  & 59.5 \(\pm\) 2.05  & 63.9 \(\pm\) 1.36  & 61.0 \(\pm\) 2.14  & 54.7 \(\pm\) 1.67  & 57.0 \(\pm\) 2.28  \\ a* & 4.91 \(\pm\) 0.76  & 3.51 \(\pm\) 1.38  & 3.10 \(\pm\) 0.45  & 57.3 \(\pm\) 0.75  & 3.55 \(\pm\) 0.13  \\ b* & 5.28 \(\pm\) 0.47  & 5.33 \(\pm\) 0.47  & 7.39 \(\pm\) 1.37  & 10.84 \(\pm\) 1.97  & 6.77 \(\pm\) 1.29  & 10.3 \(\pm\) 1.35  \\ Hardness & 235 \(\pm\) 75.4  & 693 \(\pm\) 135  & 362 \(\pm\) 135  & 675 \(\pm\) 284  & 1193 \(\pm\) 283  & 1219 \(\pm\) 160  \\ Elasticity & 0.86 \(\pm\) 0.08 & 0.85 \(\pm\) 0.02 & 0.81 \(\pm\) 0.04 & 0.88 \(\pm\) 0.08 & 0.95 \(\pm\) 0.06 & 0.91 \(\pm\) 0.08 \\ Adhesiveness & 211 \(\pm\) 82.1  682 \(\pm\) 31.9  & 351 \(\pm\) 103  & 364 \(\pm\) 69.9  & 958 \(\pm\) 172  & 959 \(\pm\) 32.7  \\ Chewiness & 157 \(\pm\) 52.0  & 584 \(\pm\) 79.6  & 344 \(\pm\) 106  & 241 \(\pm\) 38.9  & 888 \(\pm\) 162  & 836 \(\pm\) 41.2  \\ Resilience & 0.19 \(\pm\) 0.08  & 0.20 \(\pm\) 0.02  & 0.16 \(\pm\) 0.03  & 0.21 \(\pm\) 0.03  & 0.31 \(\pm\) 0.04  & 0.32 \(\pm\) 0.05  \\ Moisture & 70.0 \(\pm\) 1.56  & 60.5 \(\pm\) 1.73  & 43.1 \(\pm\) 0.39  & 41.2 \(\pm\) 1.67  & 49.4 \(\pm\) 1.59  & 39.2 \(\pm\) 1.75  \\ \hline \end{tabular}
\end{table}
Table 1: Changes of physicochemical properties in the Hunan bacon during LTS.