## 3 Results and Discussion  
### E-Nose Analysis  
LDA is a dimensionality reduction technique for supervised learning, similar to PCA, but LDA is more outstanding in supervised discrimination [20]. As shown in Figure 1A, the \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Sensors** & **Description** & **0 d** & **7 d** & **14 d** & **21 d** & **28 d** & **35 d** & **42 d** \\ \hline W1C & Sensitive to aromatic ingredients & 4.79 \({}^{\text{b}}\) & 6.33 \({}^{\text{a}}\) & 5.83 \({}^{\text{ab}}\) & 5.16 \({}^{\text{b}}\) & 4.19 \({}^{\text{c}}\) & 4.14 \({}^{\text{c}}\) & 3.14 \({}^{\text{d}}\) \\ W5S & Sensitive to nitrogen oxides & 5.94 \({}^{\text{c}}\) & 12.52 \({}^{\text{a}}\) & 10.84 \({}^{\text{ab}}\) & 9.00 \({}^{\text{b}}\) & 5.94 \({}^{\text{c}}\) & 6.04 \({}^{\text{c}}\) & 3.9 \({}^{\text{c}}\) \\ W3C & Sensitive to aromatic ingredients & 1.77 \({}^{\text{bc}}\) & 1.99 \({}^{\text{a}}\) & 1.92 \({}^{\text{ab}}\) & 1.83 \({}^{\text{b}}\) & 1.68 \({}^{\text{c}}\) & 1.68 \({}^{\text{c}}\) & 1.5 \({}^{\text{d}}\) \\ W6S & Selective to hydrogen & 1.32 \({}^{\text{b}}\) & 1.47 \({}^{\text{a}}\) & 1.36 \({}^{\text{b}}\) & 1.27 \({}^{\text{b}}\) & 1.17 \({}^{\text{c}}\) & 1.17 \({}^{\text{c}}\) & 1.06 \({}^{\text{d}}\) \\ W5C & Sensitive to alkanes and aromatics & 1.22 \({}^{\text{bc}}\) & 1.3 \({}^{\text{a}}\) & 1.28 \({}^{\text{ab}}\) & 1.25 \({}^{\text{b}}\) & 1.19 \({}^{\text{c}}\) & 1.19 \({}^{\text{c}}\) & 1.13 \({}^{\text{d}}\) \\ W1S & Sensitive to methane & 25.73 \({}^{\text{a}}\) & 27.56 \({}^{\text{a}}\) & 25.3 \({}^{\text{ab}}\) & 22.47 \({}^{\text{ab}}\) & 18.51 \({}^{\text{ab}}\) & 17.34 \({}^{\text{b}}\) & 13.57 \({}^{\text{b}}\) \\ W1W & Sensitive to sulfides & 21.79 \({}^{\text{bc}}\) & 31.73 \({}^{\text{a}}\) & 29.67 \({}^{\text{ab}}\) & 26.35 \({}^{\text{b}}\) & 21.16 \({}^{\text{c}}\) & 21.02 \({}^{\text{c}}\) & 14.95 \({}^{\text{d}}\) \\ W2S & Sensitive to ethanol & 12.02 \({}^{\text{ab}}\) & 13.62 \({}^{\text{a}}\) & 11.88 \({}^{\text{ab}}\) & 10.14 \({}^{\text{b}}\) & 8.04 \({}^{\text{bc}}\) & 7.92 \({}^{\text{bc}}\) & 5.79 \({}^{\text{c}}\) \\ W2W & Sensitive to organic sulfides & 12.32 \({}^{\text{c}}\) & 18.76 \({}^{\text{a}}\) & 17.53 \({}^{\text{ab}}\) & 15.71 \({}^{\text{b}}\) & 12.47 \({}^{\text{c}}\) & 12.46 \({}^{\text{c}}\) & 8.53 \({}^{\text{d}}\) \\ W3S & Sensitive to alkanes & 1.15 \({}^{\text{a}}\) & 1.14 \({}^{\text{ab}}\) & 1.12 \({}^{\text{b}}\) & 1.09 \({}^{\text{bc}}\) & 1.08 \({}^{\text{c}}\) & 1.07 \({}^{\text{c}}\) & 1.05 \({}^{\text{c}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Aroma values of E-nose at different fermentation times. contribution rate of LDA main axis 1 was 75.33%, and the contribution rate of the main axis 2 was 17.4%. The cumulative variance contribution rate of the main axis 1 and the main axis 2 reached 92.7% of the original information, indicating that the two principal components of LDA analysis reflected most of the information from the original data. These results indicated that the flavor profile of fermented pork loin hams at different times differed, and the E-nose could be used to distinguish them well. Among them, the flavor profiles on the 7 th, 14 th, and 21 st days had overlapping parts. These findings combined with the results in Table 1 showed that no significant difference was found between 7 days and 14 days, 14 days and 21 days respectively. Figure 1B shows aroma profiles at different times. A total of ten aroma probes were used in the test. The substances sensitive to the sensors are shown in Table 1. As shown in Figure 1B, different fermentation times had apparent differences in flavor. On the seventh day of fermentation, all the aroma values were higher except for the W3S sensor. From 7 to 42 days, the aroma value of the fermented tenderloin ham gradually decreased, which meant that the content of aromatic ingredients, nitrogen oxides, hydrogen, alkanes, methane, sulfides, ethanol, and other components in the fermented tenderloin ham was gradually reduced.