## 3 Results and Discussion
### Analysis of Volatile Compounds
#### 3.7.1 Volatile Compounds Content
Similarly, in this study, ethyl isovalerate and methyl pentanoate were found to be higher in the BF of spoiled ham, while ethyl isovalerate was more abundant in the SM of spoiled ham. Aldehydes play a crucial role in contributing to the overall flavour of dry-cured hams due to their low odour threshold [75]. Straight-chain aldehydes are mainly generated through autoxidation and oxidative deamination-decarboxylation of unsaturated fatty acids, while branched-chain aldehydes are predominantly produced through strecker degradation of amino acids [76]. In this study, the total aldehyde content is higher in spoiled hams compared to normal hams, potentially due to increased lipid oxidation and higher TBARS values in spoiled hams. Furthermore, this difference in aldehyde content might be influenced by the salt content in the ham. Previous findings have shown that smoked dry-cured hams with higher salt content during later stages of ripening exhibit lower aldehyde content [77]. The total aldehyde content of normal ham from the same muscle was significantly lower (\(p<0.05\)) than that of spoiled ham in this study, potentially attributed to the high salt content in normal ham and its inhibitory effect on lipid oxidation [15]. The most abundant straight-chain aldehydes identified in Xuanwei ham were hexanal, nonanal, octanal, and heptanal, which originated from the oxidation of unsaturated fatty acids [78]. High levels of hexanal can result in an unpleasant, pungent, and putrid odour in dry-cured hams, while nonanal and octanal can contribute to unpleasant odours such as fat, oil, rancid or fried during ham maturation [79; 80]. The present study showed that spoiled hams exhibit a high hexanal content, implying that it may be the main factor contributing to the spoiled flavour of Xuanwei hams [40]. Furthermore, the aldehyde content of BF was higher than that of SM, possibly due to the more intense drying and ripening processes involved in SM compared to BF. During this process, aldehydes can be converted into other volatile or non-volatile compounds [81]. This finding aligns with a study on Slovenian dry-cured hams [5], demonstrating a significantly higher aldehyde content in BF compared to SM (\(p<0.05\)). Acids play a significant role in contributing to the unique flavour of dry-cured ham [82]. In this study, the total acid content was significantly higher in spoiled ham compared to normal ham (\(p<0.05\)). Among them, hexanoic acid, isovaleric acid, and valeric acid were the main acids in spoiled ham, while only hexanoic acid was detected in normal ham. The higher acid content in spoiled ham can be attributed to the microbial fermentation of free amino acids through the Strecker reaction, resulting in the production of acids [40]. According to [PERSON] et al. [83], the acids contributed to a sweatey, cheesy, putrid, and sour  
Figure 2: Radar plots of \(\mathrm{e}-\)nose response data (**A**) and e-nose PCA scores (**B**) of different muscles in normal and spoiled hams. N\(-\)SM: normal ham\(-\)semimembranosus; N\(-\)BF: normal ham–biceps femoris; S\(-\)SM: spoiled ham–semimembranosus; S\(-\)BF: spoiled ham–biceps femoris. odour. Therefore, the flavour difference between normal ham and spoiled ham in Xuanwei ham may stem from the presence of acids. There was no significant difference in acid content between the SM and the BF of normal hams, whereas a significant difference was observed in acid content between the SM and the BF of spoiled hams (\(p<0.05\)). Ketones are formed through lipid autoxidation or microbial metabolism [84]. They contribute to the aroma of dry-cured hams and have a fatty flavour associated with cooked meat and blue cheese odours [67]. In this study, 3-hydroxy-2-butanone was the main ketone of spoiled ham and normal ham. The results are consistent with previous findings on Iberian dry-cured hams [85], where 3-hydroxy-2-butanone was found in higher amounts in spoiled hams compared to normal hams.