## 3 Results and Discussion
### OAV Analysis of the Differential Aroma Substances  
Numerous volatiles have been found in various foods, and only a limited number of volatiles are considered key aroma compounds that significantly influence the overall aroma profile [42]. The quantitative abundance and threshold of aroma-related compounds in tea soup have a great contribution to the quality characteristics and flavor of tea [43]. OAVs were used to assess the contribution of aroma compounds to the aroma of tea samples, and aroma compounds with an OAV > 1 were considered to be key flavor substances [44]. In total, there were 30 out of 90 volatile compounds with OAV > 1, 19 of which were commonly shared volatile compounds among the four groups. As shown in Table 3, there were 26, 22, 25, and 23 volatile compounds with OAV > 1 in SH-S, SH-A, FD-S, and FD-A, respectively. Figure 12: Volcano plot in FD-S vs. FD-A. FD-S: Fudingdabai, spring; FD-A: Fudingdabai, autumn. Figure 13: Score plot of key volatile compounds in FD-S vs. FD-A. FD-S: Fudingdabai, spring; FD-A: Fudingdabai, autumn. Add asterisks (*) on the graph according to the size of the \(p\) value, \(p<0.05=^{***},p<0.01=^{***},p<0.001=^{***}\). In the 30 above-mentioned volatile compounds, most of them had significant differences (\(p<0.05\)) among the four groups (SH-S, FD-S, SH-A, FD-A) in their contents (Table 3). Meanwhile, there were no significant differences (\(p<0.05\)) among the four samples (SH-S, FD-S, SH-A, and FD-A) in the contents of eight volatile compounds with OAV \(>1\), including hexanal, nonanal, (\(E\))-2-nonenal, decanal, oct-1-en-3-ol, colimene, methyl salicate, and ethyl nonylate, contributing significantly to the formation of the 'aged/oily/herbal' fragrance characteristics of white tea [45]. Among the 30 volatile compounds in the four groups, the top volatile, with OAV \(>1\), was \(\beta\)-ionone, with a numerical range of 3375.147-1439.131 (Table 3). \(\beta\)-ionone has an obvious floral aroma and plays a decisive role in the formation of the good flavor of various white teas [46]. In this study, the OAV of \(\beta\)-ionone in SH-S was significantly higher than that in SH-A, while the OAV of \(\beta\)-ionone in FD-S was significantly higher than that in FD-A (Table 3). The second volatile with OAV \(>1\) was 5,6-epoxy-\(\beta\)-ionone, which is related to sweet, fruity, and floral aromas and can range from 670.916 to 1118.130 in spring teas. As we know, carotenoids function as crucial aroma precursors for the production of \(\alpha/\beta\)-ionones, \(\beta\)-cirtal, \(\beta\)-damascenone, theaspirone, and many other volatile apocroatenoids during tea manufacturing, conferring the unique flavor profiles of tea [47]. In this study, the OAVs of \(\beta\)-ionones, \(\alpha\)-ionones, and 5,6-Epoxy-\(\beta\)-ionone in spring tea (SH-S, FD-S) were significantly higher than that in autumn tea (SH-A, FD-A) (Table 3). As an oxidized derivative of \(\beta\)-carotene, \(\beta\)-cyclocitral was detected in four samples, and the content in FD-S was significantly higher (\(p\leq 0.05\)) than in FD-A. This result aligns with reports indicating significantly higher concentrations of carotenoid-source volatile compounds in spring green teas than in autumn ones [14]. Research attributes this to carotenoid regulation by light and temperature, with their content peaking in spring teas [48]. In addition, the oxidative degradation of \(\beta\)-carotene is affected by lipoxygenenses (LOXs) with seasonal activity changes, which contribute to the formation of volatile derivatives of carotenoids [49]. As a product of glycosides, the third OAV was linalool, with a numerical range of 348.887-464.531 (Table 3). Linalool has the obvious aroma of lily, sweet, grape-like, and woody, which has an important influence on the formation of excellent aroma flavor of white tea, black tea, green tea, and oolong tea [50; 51; 52]. In spring, the OAV of linalool in 'Fudingdabai' was higher than that in 'Sanhua1951', which was consistent with the aroma results of the sensory evaluation (Table 1).