## 3 Results
### Identification of Volatile Organic Compounds by HS-SPME-GC-Ms
#### 3.4.1 Characterization of VOCs in Different Fermentation Groups
cerevisiae_ strains. Higher alcohols were produced by _S. cerevisiae_ through the Ehrlich pathway by degrading amino acids [20]. [PERSON] et al. [25] indicated that excessive levels of higher alcohols can lead to an unpleasant taste, while insufficient levels may result in a thin body. The alcohol content in the ET008-c54 and SY fermentation groups (2094.17 \(\mathrm{\SIUnitSymbolMicro g}\)\(\cdot\)L\({}^{-1}\), 1914.73 \(\mathrm{\SIUnitSymbolMicro g}\)\(\cdot\)L\({}^{-1}\)) was significantly higher than in the EC-1118 and NM-8 groups (1694.63 \(\mathrm{\SIUnitSymbolMicro g}\)\(\cdot\)L\({}^{-1}\), 1420.56 \(\mathrm{\SIUnitSymbolMicro g}\)\(\cdot\)L\({}^{-1}\)). Isoamyl alcohol (alcohol, cheese, floral aroma) accounted for 55.84% to 62.66% of the total alcohol content, making it the primary alcohol component in the GAB, consistent with the findings of [PERSON] et al. [30]. Additionally, phenylethyl alcohol and isobutanol were also major alcohols in the GAB, contributing floral, fruity, and green aromas to the fermented alcoholic beverage. Most of the acid compounds were derived from greengage itself, with a few generated during fermentation [20]. Although the variety of acids in the GAB was limit, the concentrations of acids accounted for 29.03% to 34.92% of the total VOCs, second only to esters. Decanoic acid (803.28-1189.8 \(\mathrm{\SIUnitSymbolMicro g}\)\(\cdot\)L\({}^{-1}\)), octanoic acid (659.3-901.38 \(\mathrm{\SIUnitSymbolMicro g}\)\(\cdot\)L\({}^{-1}\)), and lauric acid (57.27-106.43 \(\mathrm{\SIUnitSymbolMicro g}\)\(\cdot\)L\({}^{-1}\)) were present in relatively high concentrations. Decanoic acid has herbal aromas, octanoic acid produces cheese and fatty aromas, and lauric acid imparts fruity and fatty aromas. The contents of all above three acid compounds were all the most abundant in the SY fermentation group. Aldehydes were mainly formed through lipid oxidation and amino acid degradation, then quickly converted into acids, resulting in their low concentration. Due to their low odor thresholds, aldehydes can still significantly impact fermented alcoholic beverage  
Figure 4: VOC analysis of different fermentation groups by gas chromatography–mass spectrometry (GC-MS): (**A**) comparison of types and quantities of VOCs; (**B**) comparison of VOC contents; (**C**) comparation of the results obtained by HS-GC-IMS and HS-SPME-GC-MS.  
flavor even at low concentrations [10]. For instance, citronellal imparted green and citrus aromas, while benzaldehyde contributed sweetness and floral aromas. Terpenes were partly derived from the fruit and exist in both free and glycosidically bound forms [31], with others being produced through the MVA pathway of _S. cerevisiae_ strains, commonly in monoterpene form [32]. Although terpene compounds were low in total concentration (14.5-18.42 ug\(\cdot\)L\({}^{-1}\)), they played an essential role in enhancing the fermented fruit alcoholic beverage aroma with their unique floral characteristics [33; 34]. Based on the identification results from GC-MS and GC-IMS, a total of 171 VOCs were detected in the GAB, as shown in Figure 4C. Comparing the two detection methods, 98 VOCs were detected only by GC-MS, 60 VOCs were detected only by GC-IMS, and 13 VOCs were detected by both. GC-MS detected a larger number of VOCs, indicating its potential to provide a broader range of odor information for the GAB. However, certain trace aldehydes, such as hexanal, propanal, and \(\beta\)-cyclocitral, were detectable only by GC-IMS, demonstrating that GC-IMS has higher sensitivity for aldehyde recognition. Therefore, combining these two analytical methods enabled a more comprehensive investigation of VOCs in the GAB.