## 3 Results and Discussion
### Volatile Compound Analysis
The largest decrease in \(\delta\)-limonene content resulted in a weaker aromatic odor from rancid samples, which was consistent with the result that the content of limonenes decreased with the prolongation of storage time and affected the flavor in fried pepper (_Zanthoxylum bungeanum_) oil [40]. Related studies have shown that limonenes were unstable and easily oxidized in the presence of oxygen [41]. The oxidation of limonenes finally produced many products such as limonene oxide, bornyl acetate, and others [42]. In this study, bornyl acetate was detected in rancid rather than normal samples, which strongly confirmed that \(\delta\)-limonene was oxidized and degraded during the rancidity process. In addition, 2,3-butanediol, as high-value chemical, has great potential for diverse industries, including food, cosmetics, agriculture, and pharmaceutical areas [43]. (\(R\),\(R\))-2,3-Butanediol and (\(R\),\(S\))-2,3-butanediol were often detected in foods or TCMs as typical volatile compounds [44; 45]. High-temperature and -humidity conditions  
Figure 3: Heat-map and HCA of volatile compounds in normal and rancid samples. N\(-\)1, N\(-\)2, and N\(-\)3 represent normal samples. R\(-\)1, R\(-\)2, and R\(-\)3 represent rancid samples. The numbers on the right represent the compound number of Table 3. The deeper the red, the higher the content; the deeper the blue, the lower the content of the compound in the samples. caused them to volatilize and their content decreased significantly, which was consistent with the result that their content decreased in dried carrots after 50 d of storage [46]. Moreover, the ethanol concentration was 4.26% in normal samples and 0.75% in rancid samples which was caused by the normal samples being stored for 6 months in high-temperature and -humidity conditions. The result was consistent with the ethanol content decrease in kombucha during storage [47]. The high-temperature and -humidity conditions led to the growth and reproduction of bacteria in a confined space, some of which could metabolize ethanol to produce acetic acid [48; 49; 50]. Correspondingly, this led to a significant increase in acetic acid in rancid samples. Anethole, as an essential oil, has good potential for use as an alternative to synthetic fungicides for the preservation and storage of foods [51]. The content of it was decreased in this study, which was not favorable for the storage of ZSS. This was consistent with the result for the anethole content of sweet fennel fruits during aging [52]. \(n\)-Hexanol was positively correlated with pleasant odor and the overall valuation of the fruits, confirming that this lipid-related volatile compound was the most important for the aroma of foods such as \"Ambrunes\" sweet cherries [53]. Similarly, the descriptive words were sweet, spice, and herbal for estragole in previous literature [54]. The decrease in their content had negative impacts on flavor and odor of ZSS in this study. 2,3,5,6-Tetramethylpyrazine was an important compound responsible for the odor and possessed a unique organoleptic characteristic that could dramatically influence the sensory properties of foods and/or TCMs [55]. Its content was also decreased in rancid samples, which diluted the aromatic odor of ZSS. 2,2,4,6,6-Pentamethylheptane was often detected in foods such as tea and herbs [56; 57], whose level became lower in rancid samples. In terms of nine increased compounds, the relative content of acetic acid had the largest increase from 7.08 to 13.30%, followed by \(n\)-octanoic acid from 0.34 to 0.54%, and \(n\)-nonanoic acid from 0.17 to 0.27%. The largest increase in acetic acid content resulted in a stronger pungent odor from rancid samples. It was speculated that this was closely related to the degradation of ethanol [47]. Similarly, the content of butanoic acid and 3-methyl-butanoic acid was also increased, which was consistent with the result that they increased in rice wine during storage [56].