## 3 Results
### Analysis of HS-SPME-GC-MS Results  
HS-SPME-GC-MS analysis was performed on the two groups of silage (Supplemental Table S1; [[https://doi.org/10.6084/m9.figshare.27959283.v1](https://doi.org/10.6084/m9.figshare.27959283.v1)]([https://doi.org/10.6084/m9.figshare.27959283.v1](https://doi.org/10.6084/m9.figshare.27959283.v1)) (accessed on 17 December 2024)), revealing differences in the number of VOCs present. Figure 6a,b show the total ion chromatograms identified by GC-MS for the two silage groups. A total of 101 VOCs were identified, including alcohols, aldehydes, esters, alkenes, ketones, heterocyclic compounds,  
Figure 5: The scores plot of PCA based on HS-SPME-GC-IMS. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Count** & **Compounds** & **CAS\#** & **Formula** & **RI** & **R\%** & **D/ms** \\ \hline
10 & 1-hexanal & C66251 & C\({}_{6}\)H\({}_{12}\)O & 791.1 & 266.58 & 1.55781 \\ \hline
11 & 3-Methyl-2-butenal & C107868 & C\({}_{5}\)H\({}_{8}\)O & 745.6 & 223.109 & 1.35592 \\ \hline
12 & 2-Methylpentanal & C123159 & C\({}_{6}\)H\({}_{12}\)O & 756.4 & 232.975 & 1.53422 \\ \hline
13 & Acetic acid propyl ester & C109604 & C\({}_{5}\)H\({}_{10}\)O\({}_{2}\) & 713.4 & 196.287 & 1.48611 \\ \hline
14 & Ethyl acetate & C141786 & C\({}_{4}\)H\({}_{8}\)O\({}_{2}\) & 616.8 & 146.897 & 1.33928 \\ \hline
15 & 3-Pentanone & C96220 & C\({}_{5}\)H\({}_{10}\)O & 692.7 & 180.722 & 1.36617 \\ \hline
16 & 1-Butanol & C71363 & C\({}_{4}\)H\({}_{10}\)O & 666.3 & 167.553 & 1.37839 \\ \hline
17 & 1-Propanol-M & C71238 & C\({}_{3}\)H\({}_{8}\)O & 569.0 & 129.339 & 1.27328 \\ \hline
18 & 1-Propanol-D & C71238 & C\({}_{3}\)H\({}_{8}\)O & 571.9 & 130.372 & 1.43829 \\ \hline
19 & Acetic acid methyl ester & C79209 & C\({}_{3}\)H\({}_{6}\)O\({}_{2}\) & 540.9 & 120.043 & 1.19872 \\ \hline
20 & Ethanol & C64175 & C\({}_{2}\)H\({}_{6}\)O & 501.7 & 108.166 & 1.14127 \\ \hline
21 & 2-Pentyl furan & C3777693 & C\({}_{9}\)H\({}_{14}\)O & 995.9 & 560.553 & 1.25404 \\
22 & Ethyl pentanoate-M & C539822 & C\({}_{7}\)H\({}_{14}\)O\({}_{2}\) & 900.1 & 389.987 & 1.26823 \\ \hline \end{tabular}  
* Rt: Represents the retention time in the capillary GC column. RI: Represents the retention index of adjacent n-alkanes before and after the peak corresponding to the target metabolite. Dt: Represents the drift time in the drift tube. M, D: Represent the monomer, dimer of the substance, respectively.  
\end{table} 
Table 3: _Cont._aromatic compounds, and hydrocarbons. The normal silage sample contains 41 VOCs, while the abnormal silage sample contains 94 VOCs. Notably, the number of nitrogen-containing VOCs in the abnormal sample is 44, accounting for more than 77% of the total compounds. Esters and acids are the most abundant compounds identified. Esters were detected in both samples. The identified esters in this sample include 2-methylbutyl hexanoate, benzoyl isothiamate, isobutyl acetate, methylazoxymethanol acetate, propane-2-isocyanate-, 1,2-ethanediol phenyl cyclic sulfite, hydrogen isocyanate, tetramethylene diisocyanate, butanoic acid, 2-hydroxy methyl ester, methoxy acetic acid, 3-methyl butyl ester, benzyl (1,2,3-thiadiazol-4-y) carbamate, and propane-1-isocyanate, totaling 13 esters identified. By contrast, abnormal silage feed contains 10 compounds, including 3-ethyl-3-pentyl methylphosphonofluoridate, hydrogen isocyanate, methyl nitrite, benzoyl isothiamate, boronic acid dimethyl ester, ethane, isothianate, phosphonoacetic acid, and tetramethyl butyric acid neopentyl ester. Notably, 3-ethyl-3-pentyl methylphosphonofluoridate is the most abundant VOC in abnormal feed and is exclusively detected in abnormal fermentation. These high concentrations of esters highlight their unique influence on the flavor characteristics of the bitter almond-flavored silage. In general, most silage has a vinegar-like taste, which is attributed to their higher acetic acid content. Two acids, acetic acid-d3 (2,2,2-D3) and octanoic acid, silver(1+) salt, were detected in abnormal corn silage.