## 3 Results and Discussion
### Volatile Compounds in Non-Smoked Bacon Analyzed via GC-IMS and GC \(\times\) GC-TOFMS
#### 3.1.2 Volatile Compounds in Non-Smoked Bacon Identified via GC \(\times\) GC-TOFMS  
The aroma compounds in non-smoked Bacon analyzed by GC \(\times\) GC-TOFMS were visualized in the form of two- and three-dimensional chromatograms. The results of the 2D and 3D chromatograms are shown in Figure 2a,b, respectively. The compounds' retention time is displayed on the I-axis, while the chemical polarity is represented on the II-axis. It could be found that the peak profiles of the three non-smoked Bacon samples were similar, indicating little variation in the species of volatile in different Bacon. The hydrocarbon content in the Chongqing bacon was significantly higher than the other two bacon samples, as indicated by the peak in the red circle in Figure 2a. This could be related to the animals' diet and the conditions in which they are raised. However, the higher content of hydrocarbons did not affect the overall aroma, as their thresholds were too high. The detailed information on GC \(\times\) GC-TOFMS is shown in Table S1. Three  
Figure 1: Fingerprints of three non-smoked Bacons, obtained with GC–IMS. (**a**) Topographic plots; (**b**) dynamic fingerprints of three non-smoked Bacon. While each column represents the same volatile compounds in several samples, each row reflects the signal peak of a single sample. Colors serve as a visual representation of a volatile compound’s content; a brighter color represents greater content.  
samples of bacon were evaluated, resulting in 188 volatile compounds which were divided into nine groups: 23 hydrocarbons, 35 aldehydes, 31 alcohols, 32 ketones, 21 esters, 13 aromatic compounds, 10 acids, 8 furans, and 15 other compounds. For bacon samples from different regions, a total of 151, 121, and 130 volatiles were detected in Yunnan, Chongqing, and Sichuan bacon, respectively, and their contents were 48,433.69, 35,643.17, and 41,027.38 ug/kg. Chongqing bacon showed the highest hydrocarbon content (4272.73 ug/kg) in the three bacon samples, which was consistent with the results displayed in the 2D and 3D chromatograms. Aldehydes play a key role in overall aroma, and 30, 24, and 22 aldehydes were detected in Yunnan, Chongqing, and Sichuan bacon with contents of 8964.78, 10178.60, and 3858.59 ug/kg, respectively. Although Yunnan bacon had the most types of aldehydes, Chongqing bacon had the highest aldehyde content. This could be attributed to the higher contents of pentanal and hexanal. The highest alcohol content was found in Yunnan bacon, reaching 7841.54 ug/kg. 1-octen-3-ol and ethanol had a higher content in non-smoked bacon. Aldehydes and alcohols comprised the primary volatile compounds found in Yunnan bacon, accounting for 18.51% and 16.19%. For Chongqing bacon, the proportion of aldehydes could reach 28.56%, which were the main volatiles. The aroma of Sichuan bacon was dominated by ketones and alcohols, accounting for 13.52% and 13.35%, respectively. Other compounds, including pyridine, pyrazine, pyrrole, and their derivatives, also play a critical role in meat aroma formation, with the highest content found in Sichuan bacon. Aldehydes and alcohols may be related to the degree of lipid oxidation. It indicates that Chongqing bacon may have the highest degree of oxidation and the most intense aroma. The degree of lipid oxidation in pork is related to its fatty acid composition, induced oxidation, and antioxidant factors.  
Figure 2: A 2D (**a**) and 3D (**b**) chromatogram of volatile compounds in non-smoked bacon via GC \(\times\) GC–TOFMS.