## 3 Results and Discussion
### Analysis of OAV, Odor Characteristic and Key Compounds in Tea with Different Types
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Compound**} & \multicolumn{2}{c}{**Ci**} & \multicolumn{6}{c}{**OAV-Splitting of Odor Characteristic**} \\ \cline{3-10}  & **(\(\mu\)g kg\({}^{-1}\))** & **OAVi** & \% & & **Woodoy** & **Floral** & **Burnt** & **Green** & **Fruity** & **Fatty** \\ \hline \(\beta\)-Cyclocitral & 0.36 \(\pm\) 0.01 & 120.00 & 39.64 & 12.00 & 0 & 0 & 24.00 & 84.00 & 0 \\ Valeraldehyde & 0.80 \(\pm\) 0.12 & 66.67 & 22.02 & 0 & 0 & 0 & 6.67 & 13.33 & 46.67 \\ \(\beta\)-Ionone & 0.32 \(\pm\) 0.02 & 45.71 & 15.10 & 22.86 & 13.71 & 9.14 & 0 & 0 & 0 \\ \(6\)-Methyl-5-hepten-2-one & 1.54 \(\pm\) 0.19 & 30.80 & 10.17 & 0 & 21.56 & 0 & 0 & 9.24 & 0 \\ \((E\),\(E\))-2,4-Hepdienal & 0.71 \(\pm\) 0.09 & 14.49 & 4.79 & 0 & 0 & 0 & 0 & 14.49 \\ Furfurral & 2.06 \(\pm\) 0.06 & 7.30 & 2.41 & 0 & 0 & 5.84 & 0 & 0 & 1.46 \\ \(1\)-Penten-3-ol & 2.59 \(\pm\) 0.12 & 7.23 & 2.39 & 0 & 0 & 2.89 & 1.45 & 2.89 & 0 \\ Hexanal & 3.29 \(\pm\) 0.10 & 6.87 & 2.27 & 0.69 & 0.00 & 0.00 & 0.69 & 1.37 & 4.12 \\ \((E)\)-3-Hexen-1-ol & 0.15 \(\pm\) 0.00 & 2.14 & 0.71 & 0 & 0 & 0 & 1.93 & 0.21 & 0 \\ \(3\)-5-Octaden-2-one & 0.23 \(\pm\) 0.01 & 1.53 & 0.50 & 0 & 0 & 1.53 & 0 & 0 & 0 \\ Total & 12.05 & 302.74 * & & 35.55 & 35.27 & 19.40 & 34.74 & 111.04 & 66.74 \\ \% ** & & & 11.74 & 11.65 & 6.40 & 11.48 & 36.68 & 22.05 \\ \hline \end{tabular} Note.: OAVi = Ci/Ti, where Ci is the content of compound i (\(\mu\)g kg\({}^{-1}\)), and Ti is the threshold value of compound i (\(\mu\)g kg\({}^{-1}\)). * OAVi = COAVi. ** \% is proportion of the each odor OAV accounting for OAVt.  
\end{table} 
Table 3: The content, OAVi and OAV-splitting of key aroma compounds in oolong tea. fragrance of red tea with distinctive fruity odor, compositing evenly odors of wood, green, and floral. In terms of aroma compounds in red tea, \(\beta\)-cyclodextrin was the first and dominant contributor for fruity odor; \(\beta\)-ionnone was the first contributor for woody odor, secondary by \(\beta\)-cyclodextrin; \(\beta\)-cyclocitral was the first contributor for green odor, secondary by (\(E\))-3-hexen-1-ol; and \(\beta\)-ionnone and 6-methyl-5-hepten-2-one were the main contributors for floral odor. There were 10 compounds with OAVi > 1 in dark tea and the OAVt was 55.98 (Table 5). They were \(\beta\)-ionone (34.29) >> 6-methyl-5-hepten-2-one (6.40) > (\(E\),\(E\))-2,4-heptalenal (5.71), as well as 7 compounds (<1.7). The OAVi of the first three compounds was much higher than that of other compounds, accounting for 82.88% of the OAVt. In terms of odor characteristics, the OAVt (55.98) of dark tea was composed of 18.37 for woody, 17.15 for floral, 9.55 for fatty, 7.50 for burnt, 2.96 for fruity, and 0.45 for green. The odors of woody (accounting for 32.81%) and floral (accounting for 30.64%) were evenly matched in the characteristics of black tea, complemented by fatty (accounting for 17.06%). These three odors (accounting for 80.51% of OAVt) formed the weak fragrance of dark tea with odors of woody and floral, compositing of mild fatty. In terms of aroma compounds in dark tea, \(\beta\)-ionone was the first and dominant contributor for woody, floral and burnt odors; (\(E\),\(E\))-2,4-heptalenal was the first and dominant contributor for fatty odor. It is well-known that the number and the content of tea volatile compounds could not accurately represent the aroma quality of tea. The result of OAVt of the five tea samples was green tea (492.02) \(\approx\) red tea (471.88) > oologo tea (302.74) >> white tea (68.10) \(\approx\) dark tea (55.98) (Tables 1-5). These results suggested that green, red, and oologe teas are high-aroma teas, while white tea and black tea are low-aroma types. This conclusion is surprisingly consistent with the sensory cognition of the general public on these five types of tea, that is, green, red, and oologo teas are considered strong-flavor tea and white and black teas are mild-flavor teas [24]. More and more studies have reported on the tea aroma characteristics by using the OAV method. [PERSON] et al.