## 2 Results and Discussion
### Aroma Recombination and Omission  
To investigate key aroma-active compounds, a common approach involves systematic omission tests coupled with sensory evaluation. This assesses whether the omission of an individual compound results in a significant divergence from the overall aroma profile. Consequently, reconstitution experiments are essential. These experiments require the preparation of a sensorially accurate replica of the original sample's aroma profile. This is achieved by quantitatively recombining the maximum feasible number of identified volatile compounds, utilizing authentic chemical standards at their accurately quantified concentrations. The validated reconstitution model then serves as the baseline for subsequent omission studies. Aroma recombination tests were performed by reconstituting volatile compounds with odor activity values (OAVs) > 0.1 into a 60% (\(\
icefrac{{v}}{{v}}\)) ethanol-water solution, based on the precise quantitative results of G-0 (young Baijiu) and G-15 (aged Baijiu) (Figure 4). The reconstituted samples were then subjected to comparative analysis of aroma characteristics against the original liquors. This approach enabled the establishment of a predictive model to delineate the distinct aroma profiles of young and aged _Nongxiangxing_ Baijiu. The aroma profile plots revealed no significant differences in flavor intensity between the reconstituted models and the original samples across nine sensory attributes: fruity, jiao-aroma, sweet, grain, alcoholic, burnt, floral, sour aroma, and oxidized oil. However, discrepancies were observed in specific attributes. For the G-15 model, the intensities of burnt, oxidized oil, and fruity notes were not fully replicated compared to the original aged samples. Similarly, the G-0 model failed to completely restore the jiao-aroma characteristic of the young Baijiu. Despite these limitations, the reconstituted Baijiu samples were  
Figure 4: Aroma profiles of G-0 Baijiu (**a**), G-15 Baijiu (**b**), and their aroma-reconstituted models. demonstrated to effectively reconstruct the overall flavor profile of the originals when evaluated against the nine aroma descriptors. These findings highlighted the critical role of the identified aroma compounds in defining the sensory identity of Baijiu and validated the precision of the quantitative analytical methodology employed. In the reconstituted aged Baijiu samples, the contribution of ten key aroma compounds--vanillin, 4-methyl-2-methoxyphenyl, 4-ethyl-2-methoxyphenyl, benzaldehyde, \(\beta\)-phenylethanol, 3-(methylsulfanyl)propan-1-ol, Nonan-4-olide, 3-(methylsulfanyl)propanal, linalool, and 2,3,5,6-tetramethylpyrazine--to the aroma profile of aged _Nongxiangxing_ Baijiu was systematically investigated using the triangular test method. These compounds had been previously identified as exhibiting significant positive correlations with storage duration. As shown in Table 3, highly significant differences (\(p<0.001\)) were detected by 18, 16, and 18 out of 20 panelists for the omission models of 4-methyl-2-methoxyphenol, 3-(methylsulfanyl)propanal, and 3-(methylsulfanyl)propanal, respectively. These results indicated that the smoky odor attributed to 4-methyl-2-methoxyphenyl, the roasted meat-like aroma from 3-(methylsulfanyl)propanal-ol, and the musty tomato-like note associated with 3-(methylsulfanyl)propanal are critical trace aroma compounds contributing to the aged _Nongxiangxing_ Baijiu profile. Significant differences (\(p<0.01\)) were also observed when \(\beta\)-phenylethanol, benzaldehyde, and linalool were omitted from the reconstituted samples, underscoring their roles in imparting floral and sweet notes, which are essential to the characteristic flavor of aged _Nongxiangxing_ Baijiu. In contrast, the omission of vanillin, 4-ethyl-2-methoxyphenyl, nonan-4-olide, and 2,3,5,6-tetramethylpyrazine did not yield statistically significant differences.