## 3 Results and Discussion
### Key Aroma Compounds in Non-Smoked Bacon Identified via GC-O-Ms  
AEDA proves to be an efficient method of assessing the impact of individual odor-active compounds on the overall aroma. The aroma in the sample was continuously diluted until assessors could not detect anything. The aroma compounds could be detected with a high FD factor, and they could be identified as key aroma compounds. Due to the complexity of the matrix, the use of chromatographic columns with different polarities can obtain a better separation effect and accurate qualitative analysis. The results of compound identification via GC-O-MS are shown in Table 2. A total of 76 volatile compounds were detected in three non-smoked bacons via GC-O-MS, comprising 49 aroma compounds detected through assessors and mass spectrometry, with 25 volatiles solely identified through mass spectrometry. The other two unknown compounds could only be sniffed by assessors via an olfactometer. These two compounds also have a significant contribution to overall aroma and present mushroom and rice aromas. As shown in Table 2, a total of 13 aldehydes, 10 alcohols, 12 ketones, 13 esters, 6 aromatic compounds, 8 hydrocarbons, 10 acids, and 2 other compounds were detected in the three bacon samples. The concentration and OAV values of each volatile compound are shown in Table 3.  
Aldehydes: Aldehydes, both saturated and unsaturated, are a significant contributor to the aroma of meat and meat products due to their low threshold [20]. In this study, Sichuan bacon contained 12 aldehydes; Chongqing and Yunnan bacon had 10 and 9 aldehydes, respectively. Meanwhile, the total concentrations in Yunnan, Sichuan, and Chongqing bacon were 1263.73 \(\pm\) 14.86, 2818.54 \(\pm\) 53.99, and 1774.5 \(\pm\) 42.45 \(\upmu\)g/kg. Hexanal, (E)-2-nonenal, and (E,E)-2.4-decadienal were found to be significant in the three bacon samples due to their high FD factor (FD \(\geq\) 27). These compounds are believed to be the primary aldehydes responsible for the aroma of non-smoked bacon. The hexanal concentration was the highest among all volatile compounds in three bacon samples (868.55 \(\pm\) 41.46, 628.88 \(\pm\) 28.47, and 1123.21 \(\pm\) 66.27 \(\upmu\)g/kg in Yunnan, Sichuan, and Chongqing bacon). Other aldehydes such as 2-undecenal, octanal, and heptanal were also considered as key aroma compounds in Chongqing and Sichuan bacon. More aldehydes appeared in Sichuan bacon, so nonanal and decanal contributed significantly to the overall aroma of Sichuan bacon. Aldehydes were known to provide a fatty, green, and fresh aroma, and they were derived primarily from the lipid oxidation and Strecker degradation of \(\alpha\)-amino acid [21]. Hexanal exhibited the highest FD factor among the aldehyde compounds, and these straight-chain aldehydes primarily originated from the oxidation of both unsaturated and saturated fatty acids [10]. In addition to hexanal, octanal, nonanal, decanal, (E)-2-ocenal, (E)-2-nonenal, (E,E)-2-decadienal, (E)-2-decenal, 2-undecenal, and heptanal were also straight-chain aldehydes, and all contributed significantly to the overall aroma. These findings align with prior research indicating that hexanal is the predominant aldehyde in dry-cured meat products, including lacon, ham, and chorizo [22]. Linoleic acid may serve as the precursor for the formation of hexanal, heptanal, octanal, and nonanal via the autoxidation of oleic fatty acid [22]. Fatty acids were oxidized into different hydroperoxides via enzymatic oxidation or autooxidation, and these hydroperoxides could degrade into various aldehydes [23]. The aldehydes identified through GC-O-MS were solely straight-chain aldehydes, while a few branched-chain aldehydes were detected through GC-IMS. These aldehydes present fatty and green notes but have an unpleasant rancid aroma at an excessive concentration. (E)-2-nonenal and (E,E)-2.4-decadienal contribute distinct nuances to the aroma profile, with (E)-2-nonenal offering a fatty, waxy scent and (E,E)-2,4-decadienal providing a pungent, fatty aroma.