# Variation in Volatile Flavor Compounds of Cooked Mutton Meathalls during Storage
## 3 Results
### Analysis of Volatile Flavor Compounds in Cooked Mutton Meatballs during Storage  
It can be seen from Figures 1 and 2 that the content of hydrocarbon substances is high in various volatile compounds during each storage period. Oefins generally have a higher odor threshold and do not contribute much to the overall aroma. However, like aldehydes, they are both products of fatty acid breakdown and intermediates of heterocyclic substances, so the variation trend of their concentration has a certain correlation with the presentation of flavor [27]. Oefins are mostly related to species, such as \(\alpha\)-copaene and 3-carene, which are among the main components of turpentine and have the aroma of turpentine. 1-methyl-4-(6-methylhept-5-en-2-yl)benzene is found in codonopsis, dried ginger and American ginseng. Sulphur-containing compounds such as allyl methyl sulfide, diallyl sulfide, diallyl disulfide and garlic are related components. Garlic is used to make the mutton meatballs, giving them a strong garlic smell and helping to mask the goat-like odor. Whether SPME or SAFE, sulfur compounds have a higher proportion and concentration in the total volatiles. By SPME/GC-O-MS, seven kinds of volatile sulphur-containing compounds were extracted; of them, four kinds could be smelled. By SAFE/GC-O-MS, four kinds were extracted and three kinds were smelled, indicating that sulfur compounds contribute more to the overall aroma components of cooked mutton meatballs. Aldehydes are usually the products of oxidative degradation of fat, and the volatile compounds of aldehydes in cooked mutton meatballs are not high. Although the relative content is not high, the threshold value of aldehydes is low, which contributes to the overall degree of mutton meatball [28]. Hexanal and nonanal can be smelled by SPME and SAFE/GC-O-MS, which is consistent with the research results of the characteristic aroma components of Ningxia Tan mutton [29]. Both SPME and SAFE/GC-O-MS analysis showed a decrease in the relative content of aldehydes at the later stage of storage, indicating that flavor loss was relatively serious at the later stage of storage, which was consistent with the results of sensory evaluation. Alcohol compounds may be produced by the microbial metabolism of glucose and amino acids or may be caused by the oxidation of fatty acids. The threshold value of alcohol compounds is generally high, and it does not contribute much to the flavor of cooked lamb meatballs during storage [29]. Esters and ketones were relatively high in cooked mutton meatballs, but the volatile compounds retrieved were not smelled, which contributed little to the overall aroma of cooked mutton meatballs [30]. Phenols were detected only in SAFE/GC-O-MS, and their proportion gradually increased from 5.68% to 14.84% in the storage process. Among the five detected phenolic substances, only 2,6-ditert-butyl-4-methylphenol could be smelled, but the intensity of the smell was not large. The key odor-active substances in cooking mutton meatballs during different storage periods were identified. Among the many volatile compounds in cooked mutton meatballs, only a small part of them play an important role in contributing to the overall flavor, and these odor-active compounds are the main aroma components in cooked mutton meatballs. In order to further determine the degree of aroma contribution to the storage period, the flavor dilution factor of the odor-active compound, namely the FD factor, can be obtained by gradual dilution. The larger the FD factor, the greater the contribution of the odor-active compound to the cooked mutton meatballs is. The FD factor is used to evaluate how much these flavor compounds contribute to the overall aroma. It can be seen from Tables 3 and 4 that, among the volatile flavor components extracted by SPME, the number of compounds that could be smelled were 21, 21, 17 and 13. While for SAFE, the number of odor-active compounds identified were 13, 24, 20 and 12.