## 3 Results and Discussion
### Odor-Active Compounds Detected Using GC-O  
The volatile isolates of six CSSs obtained via SE-SAFE and SPME were analyzed by means of GC-O; the odor-active regions were detected. To identify the structures of the odor-active compounds, their odor characteristics, mass spectra data and RIs were compared with the data obtained from the published literature and authentic standards. The results are listed in Table 1.  
A total of 55 aroma-active compounds were identified from six CSSs on the DB-Wax and HP-5 columns in Table 1, including 10 esters, nine carboxylic acid, nine pyrazines, seven aldehydes, seven ketones, five alcohols, four phenols and four sulfur-containing compounds. Of 55 compounds, six odorants (1, 4, 5, 12, 27 and 41) were only identified in SPME isolates; most of them had lower boiling points. Meanwhile, eight odorants (20, 29, 31, 33, 35, 40, 47 and 53) were only identified in SE-SAFE isolates, and they had higher boiling points. The number of odorants identified in C1, C2, C3, J1, J2 and J3 were 44, 45, 43, 40, 45 and 44, respectively; there were 33 compounds in common for the six CSSs. Ten ester compounds (2, 5, 6, 8, 10, 11, 28, 33, 41 and 53) were detected as odor-active compounds in six CSSs. Of the 10 ester compounds, nine esters were ethyl esters. All of them had been identified as volatile compounds in Chinese SS [9; 12], Japanese SS [7], Thai SS [13] or Korean SS [14; 15]; most of them had also been identified as odor-active compounds in SS; for example, ethyl propanoate, ethyl 2-methylpropanoate, ethyl butanoate, ethyl 2-methylbutanoate, ethyl 3-methylbutanoate and ethyl phenylacetate had been found in Japanese SS as aroma-active compounds [7; 16]; ethyl acetate and ethyl propanoate had been identified as odorants in Chinese SS [8]. However, as odor-active compounds in SS, \(\gamma\)-dodeclactone and ethyl 2-hydroxy-4-methylpentanoate (EHMP) had not been reported. As SS volatiles, \(\gamma\)-dodeclactone was only identified in SS manufactured using _Bacillus_ species and fused yeast [15], and EHMP only in Chinese SS [12] by MS. EHMP was a very important flavor compound; it occurred in fresh fruits, grape brandies, wines, etc. When this ethyl ester was mixed with C4-C10 alkanoic acids, it could enhance natural, ripe and tropical fruit flavors. It may have contributed greatly to the fruity odor of SS [17]. All of the esters identified were thought to be a result of two pathways. The first was the metabolism of yeasts. In the production process of SS, a variety of microorganisms, including yeast, lactic acid bacteria, _Aspergillus oryzae_, etc., were used. During SS fermentation, some esters were formed enzymatically through the metabolism of yeasts. The second pathway was the reaction of alkanol with organic acid during sterilization and storage; because the reaction was non-enzymatic catalysis, the reaction rate was slow, and the number of esters formed was less. The production of esters depended on many factors, such as aeration, concentrations of organic acids, alcohols and their precursors, etc. [18]. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No. **} & \multirow{2}{*}{**Compound**} & \multicolumn{2}{c}{**RI**} & \multirow{2}{*}{**Odor Quality**} & \multicolumn{2}{c}{**Chinese CSSs**} & \multicolumn{2}{c}{**Japanese CSSs**} & \multirow{2}{*}{**Isolate \({}^{\ast}\)**} & \multirow{2}{*}{**Identification \({}^{\ast}\)**} \\ \cline{3-3} \cline{5-12}  & & **DB-Wax \({}^{\ast}\)** & **HP-S \({}^{\ast}\)** & & & & & & & & & & & \\ \hline  
Nine carboxylic acids (23; 29; 31; 35; 37; 40; 42; 43 and 55), including four linear-chain carboxylic acids, four branched-chain carboxylic acids and one aromatic acid, were identified as odorants in six CSSs; acetic acid, butanoic acid, 3-methylbutanoic acid and 3-methylpentanoic acid were the common substances in six samples.