## 3 Results and Discussion
### GC-MS Analysis Results
#### 3.2.1 Contents and Types of Volatile Substances in Oysters with Different Freshness  
Figure 7 and Table 6 illustrate the relative contents of volatile compounds in oysters stored at various temperatures over time. As depicted in Figure 7a, at 4 \({}^{\circ}\)C, there is no significant difference in the relative content of alcohol, nitrogen-containing, and phenolic compounds as storage time increases. Additionally, the relative content of aldehyde compounds shows a decreasing trend, while the relative content of acid compounds exhibits an initial decrease followed by an increase. Additionally, the relative content of hydrocarbon, ketone, and ester compounds demonstrates an initial increase followed by a decrease. In Figure 7b, at 12 \({}^{\circ}\)C, it can be observed that the relative content of alcohol compounds tends to decrease with increasing storage time. Aldehyde and hydrocarbon compounds display a trend of initially decreasing followed by an increase in relative content during storage. The relative content of acid compounds shows an initial increase followed  
by a decrease. There are no significant differences in the relative content of ketone, nitrogen-containing, and ester compounds. In Figure 7c, at 20 \({}^{\circ}\)C, it is evident that the relative content of alcohol substances decreases initially and then increases during the storage process. The relative content of ketone substances increases initially and then decreases over time. The trends for acid substances and nitrogen-containing compounds also show an initial increase followed by a decrease during storage. No significant differences are observed in the relative content of aldehyde, hydrocarbon, and ester substances. In Figure 7d, at 28 \({}^{\circ}\)C, the relative content of aldehyde substances initially decreases before increasing again during the storage process. In contrast, hydrocarbon substances exhibit an initial increase followed by a decline. The relative content of ester substances shows a significant increase, whereas alcohol substances, ketone substances, and nitrogen-containing compounds demonstrate a decreasing trend throughout storage. Notably, no significant difference was observed in the relative content of acid substances, indicating that these compounds may not be key markers for freshness assessment in this context. Despite the numerous volatile organic compounds identified and tracked over time, the limited variation in acid compounds suggests that other pathways, such as the formation of heterocyclic compounds like cis-2-(2-Pentenyl)furan, play a more crucial role in the degradation process. Figure 7: Relative contents of various volatile substances: **(a)** 4 \({}^{\circ}\)C, **(b)** 12 \({}^{\circ}\)C, **(c)** 20 \({}^{\circ}\)C, **(d)** 28 \({}^{\circ}\)C.  
Figure 8 and Table 7 illustrate the comparison of volatile compounds in oysters at various storage temperatures. In Figure 8a, at 4 \({}^{\circ}\)C, the diagram reveals that during storage, oysters contain a substantial number of alcohols, hydrocarbons, and esters, which indicates their significant role in the volatile substances present in oysters. Conversely, the levels of phenols and ethers are relatively low. In Figure 8b, at 12 \({}^{\circ}\)C, it can be observed that the storage process results in a higher concentration of alcohols, hydrocarbons, and esters, further underscoring their importance in the volatile profile of oysters. Similarly, phenolic and ether compounds remain at lower concentrations. Figure 8c, at 20 \({}^{\circ}\)C, shows an increased presence of hydrocarbon compounds, along with relatively high levels of alcohols, aldehydes, and acids. In contrast, nitrogen-containing compounds, phenolic compounds, and ether compounds are found in lower quantities. Lastly, Figure 8d, at 28 \({}^{\circ}\)C, indicates that the storage process leads to a notable increase in ester compounds, alongside significant amounts of hydrocarbons, alcohols, aldehydes, and acids. Conversely, nitrogen-containing and ketone compounds are present in lower quantities.