## 4 Conclusions  
In this study, both temperature at 40 \({}^{\circ}\)C and relative humidity of 75% were set up to carry out the accelerated rancidity process for obtaining the rancid ZSS samples from normal ZSS samples over 6 months of storage time. It is worth noting that these storage conditions were not set at random, but were determined according to the parameters of the accelerated test and the drug stability investigation test, which could reflect the change process of substances and the stability of related physicochemical indicators [70; 71; 72]. In recent years, the condition of 40 \({}^{\circ}\)C and 75%RH was often used to evaluate the related changes and mechanisms during the storage of TCMs, foods, functional beverages [73], and cosmetics [74], such as pecan [75], Benjakul [76], _Salvia miltiorrhizia_[77], and _Piper Ihotzkyanum_ Kunth leaves [78]. After 6 months of storage, there was a significant difference between normal and rancid samples of ZSS. The most intuitive change is in traditional sensory properties, including the rancid samples producing a darker color, a bitter taste, and an irritating odor. This was consistent with the results that wild almond kernel, perilla seed, and beef samples became a darker color and had an unpleasant odor [79; 80; 81]. In addition, the physicochemical indicators such as moisture content, water- and alcohol-soluble extracts, and acid value were also detected. Among them, the acid value had a significant difference (\(p<0.01\)), from 3.90 of normal ZSS to 18.68 mg/g of rancid ZSS. This was consistent with the results that the acid value had a significant increase in wild almond kernel from 0.07 to 0.83 mg/g after 30 d at 25 \({}^{\circ}\)C, large yellow croaker (_Larimichtphys crocea_) from 2.02 to 7.62 mg/g after 120 d at 75%RH, peanut from 0.09 to 0.62 mg/g after 10 months at 35 \({}^{\circ}\)C, and green coffee beans from 0.65 to 1.28 mg/g after 20 days at 60 \({}^{\circ}\)C during storage link [81; 82; 83; 84]. In order to further explore the changes in chemical composition from normal to rancid ZSS samples, HS-SPME-GC-MS technology was used to detect the volatile compounds. As a result, 39 volatile compounds were identified in ZSS samples, including 20 volatile compounds in normal samples and 38 volatile compounds in rancid samples. Nineteen common compounds were identified in normal and rancid samples. Among them, the content of 10 compounds such as \(\delta\)-limonene, (\(R\),\(R\))-2,3-butanediol, and (\(R\),\(S\))-2,3-butanediol was decreased but that of nine compounds such as acetic acid, \(n\)-octanoic acid, and \(n\)-nonanoic acid was increased in rancid samples. Nineteen unique compounds such as \(\beta\)-phellandrene, \(\alpha\)-pinene, and 3-carene were detected and only one compound, \(\delta\)-cadinene, was not detected in rancid samples. It was speculated that \(\delta\)-cadinene might be decomposed and 19 compounds were brought out in the rancidity process. It is worth noting that the total content of 11 organic acids such as acetic, propanoic, and butanoic acids in rancid samples was increased. This was consistent with the results that the content of some organic acids increased after the rancidity of high-quality extra virgin olive oils, French fries, poppy seeds, and sunflower seeds [85; 86; 87; 88]. Among the many volatile compounds in the rancid samples, only some of them played an important role in contributing to the overall odor. Eight short-chain organic acids, acetic, propanoic, butanoic, pentanoic, hexanoic, heptanoic, octanoic, and nonanoic acids, were new products in rancid ZSS samples, and it was speculated that the production of a series of organic acids might be the material basis of irritating odors after normal ZSS became rancid. This is the first report that a series of short-chain organic acids have been found in a rancid substance.