## 3 Results and Discussion
### OAV Analysis of Differential Aroma Compounds  
GC-Q-TOF-MS analysis was successful in characterizing and quantifying volatile aroma components. However, it was unable to specifically identify the characteristic aroma compounds responsible for the aroma profiles of the four sample groups. To address this limitation, we used the OAV of volatiles to identify the major volatiles present in the four samples subjected to different fermentation methods. By calculating the OAV of the potentially labeled aroma compounds, a total of 34 aroma compounds were identified (Table S3). These compounds encompass a range of sensory aromas, such as woody notes represented by (\(-\))-4-terpineol, herbal notes represented by methyl salicate, stale notes represented by 1,2-dimethoxybenzene, fruity notes represented by benzyl alcohol, and floral notes represented by linalool. In addition, the analysis revealed the presence of other aroma compounds with distinct profiles, such as acetophenone with an almond aroma and 1-octen-3-ol with a mushroom aroma.  
The key aroma compounds with OAV > 1 in the four groups of samples were screened to create the flavor wheel. The aroma types of Liupao tea were mainly dominated by stale and woody aromas; however, the specific aroma components differed in type and quantity (Figure 4a-d). The OAVs of these characteristic aroma compounds of different aroma types in each group were further quantified (Figure 4e). Differences were observed in the OAV cumulative quantization values of the different aroma types across the four groups of Liupao tea samples. The OAV cumulative quantization values for the DM1 group, specifically for stale and woody aromas, were significantly higher compared to the other groups. The OAV cumulative quantization value for the stale aroma feature was notably high, reaching 148.1. Stale aroma is a distinctive characteristic of high-quality Liupao tea and is positively correlated with its overall quality [5]. In general, the DM1 group exhibited prominent stale and woody aroma characteristics compared to the other groups using different fermentation methods; moreover, in the OAV, accumulation values for other aroma types were also higher, indicating superior overall aroma quality.  
Figure 4: Flavor wheel of key volatile compounds in the four types of Liupao tea samples. DMI group (**a**); DI group (**b**); CI group (**c**); CMI group (**d**); cumulative quantitative bar chart of OAV (**e**).  
The greater the OAV of an aroma compound, the greater its influence on the sample aroma. When the OAV \(>\) 10, the compound is considered to have a significant contribution to the overall aroma of the tea [37]. A screening of key characteristic aroma compounds was further carried out with OAV \(>\) 10 as the screening condition, as shown in Figure 5. The analysis revealed that the characteristic aroma compounds shared among the four fermentation methods used in the production of Liupao tea are 1,2,3-trimethoxybenzene with a stale aroma and nonanal with floral and fruit aromas. In the Cl group, octanal provided a strong fruity aroma, which made an important contribution to the fruity characteristics of this group. The CMI group was characterized by ecdrol with a woody fragrance, while the DI group contained ecdrol as well as \(\beta\)-Dihydro-ionone, offering both floral and woody notes. It is worth noting that the aroma profile of the DMI group exhibited greater diversity compared to the other three groups. This observation may be attributed to the inoculation of raw materials with _M. purpureus_ during the initial steaming process. The presence of _M. purpureus_ appears to enhance the abundance of aromas in the DMI group, contributing to its unique profile [38].