## 4 Discussion  
Strong-aroma baijiu possesses a highly complex aroma profile. In this study, the results from GC-O and quantification revealed that several compounds, including ethyl butyrate, ethyl pentanoate, ethyl hexanoate, butyl hexanoate, ethyl 3-methylbutyrate, and hexanoic acid, significantly contribute to the aroma characteristics of strong-aroma baijiu. These findings are consistent with reports in previous studies that esters, especially ethyl ester compounds, were the most important aroma compounds in baijiu [19; 20; 21]. The aroma composition of baijiu warrants further investigation because, in addition to the essential role of the main compounds in defining its overall aroma profile, certain trace components with low odor thresholds also significantly influence its aromatic characteristics, such asfuran derivatives, sulfur-containing compounds, and pyrazines. It is important to note that both the Osme values and the concentrations of most aroma compounds varies significantly across different samples. Generally, samples from the Sichuan region exhibited generally higher total concentration of esters (e.g., ethyl pentanoate, amyl acetate, methyl hexanoate), while those from the Jianghuai region contained more alcohols compared to Sichuan samples. Other variations in trace components also likely contribute to the flavor differences in strong-aroma baijiu from various production regions. For instance, compounds such as 2-heptanone, 2,6-diethylpyrazine, tetramethylpyrazine, 2-acetylfuran, and 5-methylfurfural showed higher aroma intensities in samples WLC and WLY from the Sichuan region compared to the YH and GJ samples from the Jianghuai region. In particular, heterocyclic compounds contribute to roasted, baked, and smokoy aroma characteristics. Previous studies have highlighted that 2,6-dimethylpyrazine is a crucial aroma compound in strong-aroma baijiu [22], while tetramethylpyrazine offers a unique flavor reminiscent of popcorn and nuts [23], which were also the key aroma-active compounds in the fermentation starter (Daqu) of strong-aroma baijiu [24]. Additionally, furfural has been identified as an important compound for bitterness and baked notes in baijiu [25]. Furthermore, 2-acetylfuran has been found in strong-aroma baijiu, contributing to its roasted aroma [21]. Thus, it can be inferred that heterocyclic compounds such as furans and pyrazines are characteristic aroma compounds that distinguish strong-aroma baijiu from those produced in the Jianghuai and Sichuan regions, consistent with the findings reported by [PERSON] et al. [26]. We observed that compounds such as isobutyl acetate, ethyl octanoate, and ethyl isovalerate were present in higher concentrations in the YH and GJ samples compared to the WLC and WLY samples. This difference might be attributed to the lower fermentation temperature (usually between 25-32 \({}^{\circ}\)C) of the Jianghuai samples, which likely allowed for the retention of more short-chain esters [27]. In the recombination tests, aroma-active compounds were found to be crucial for the aroma of baijiu, while non-volatile compounds also significantly influenced its aroma profile. The scores for most aroma attributes in Rec B (full model) were significantly higher than those in Rec A (only volatiles). This indicates that non-volatile compounds have a notable enhancing effect on aroma perception. This enhancement may be due to non-volatile compounds altering the liquid-air partition rate of the volatiles, thereby increasing the amount of volatiles in the headspace. Our results are aligned with a recent report on soy sauce-aroma baijiu that the intensities of floral, fruity, acidic, and grain aromas of the fourteen key aroma-active compounds were enhanced in the presence of non-volatiles [10]. [PERSON] et al. [16] specifically studied the perceptual interactions between lactic acid and ethyl lactate and found that lactic acid created additive or synergistic odor effects with both ethyl lactate and ethyl acetate.