# Characterization of Quality Properties in Spoiled Mianning Ham
## 3 Results and Discussion
### Flavor Compound Analysis
The contribution value of 1-Octen-3-ol to the aroma was greater in normal Mianning ham. However, their abundance was rather low, as indicated by 2-heptanone and 1-octen-3-one with 0.21% and 0.03% in Nuodeng ham, respectively [42]. Aldehydes usually have low thresholds and strong odors and play an important role in meat product flavor formation, where most straight-chain aldehydes are produced by auto-oxidation and oxidative deamination-decarboxylation of unsaturated fatty acids and most branched-chain aldehydes are produced by Strecker degradation of amino acids [4]. Spoiled ham contains higher levels of aldehydes than normal ham, with hexanal and nonanal being the most abundant aldehydes in many dry-cured hams. In mature Kumpiak podlaski ham, hexanal is the predominant flavor compound [45]. Large amounts of hexanal are often found in Iberian and Parma hams, which is considered as distinctive trait of these products [46]. Hexanal has a grassy smell, while heptanal, octanal, and nonanal have a fatty aroma [47]. These aldehydes have a low threshold and generally play a positive role in the formation of product aroma at low concentrations, while at higher concentrations, they become a major source of off-flavors [46]. This is one of the possible reasons for the formation of odor in deeply rotten hams. Ketones are intermediate products of lipid oxidation and can be formed by the chemical auto-oxidation of free fatty acids [48]. 2-Nonanone has a soapy odor, which may be  
Figure 5: Heat map of hierarchical clustering analysis of main flavor substances in Mianning ham. Each row represents a flavor substance and each column represents a ham sample. The redder the color, the higher the content of volatile compounds; the bluer the color, the lower the content of volatile compounds. related to the formation of off-flavors in the late stages of ham storage and contributes to the odor of deeply spoiled ham. 2-Nonanone is formed in small quantities in chemical reactions but in a large part is derived from micro-organism metabolism such as carbohydrate fermentation, lipid and ethyl esters oxidation, and amino acid catabolism [49]. Therefore, the high content of 2-nonanone in our present study indicates the development of spoilage microflora during ripening. [PERSON] et al. reported similar results, suggesting that the increase in ketones in Iberian ham was related to the activity of spoilage microorganisms [50]. In previous research 2,3-octanedione was detected in Shinkenspeck and Parma ham. 2,3-Octanedione is rarely either present or the dominant ketone in the profile of volatile compounds in dry-cured hams. Spanish and French hams have the highest concentrations of 2-propanone [3]. The production of alcohols is closely related to amino acid metabolism, fat degradation and oxidation, methyl ketone reduction, and microbial growth and reproduction [51]. Usually, alcohols have a high threshold and contribute less to the flavor of the product. However, some unsaturated alcohols were detected in all three hams, such as 1-octen-3-ol and 2-propyl-1-pentanol. These alcohols have low thresholds and may play an important role in aroma variation. Among them, 1-octen-3-ol, formed by the oxidation of arachidonic acid, is frequently detected in dry-cured ham and is considered to be the characteristic flavor substance of Panxian ham, Jinhua ham, and Rugao ham [19; 52]. Esters are derived from the esterification of carboxylic acids and alcohols. Esters of short-chain acids have a fruity and sweet taste, but long-chain acids produce a fatty odor [53]. Most esters have a low sensory threshold, and the aroma of dry cured ham is often attributed to the fruity odor of the ester [54]. Thirteen esters were detected in spoiled Mianning ham, while only three esters were detected in normal Mianning ham. Another source of esters may be the unique microbiota that emerge during the ripening period of dry-cured ham.