## 3 Results and Discussion
### Analysis of OAV, Odor Characteristic and Key Compounds in Tea with Different Types
used the OAV method to study the aroma characteristics of Longing tea (a green tea) and found that the OAV of geraniol, epoxylinalool, (\(Z\))-neroidold, 2-ethyl-3,5-dimethylpyrazine, and \(\beta\)-ionone were relatively high [25]. [PERSON] et al. reported that 14 compounds were the key aroma compounds of Longing tea based on the gas chromatography-olfactometry (GC-O), OAV method and an aroma recombination experiment [10]. [PERSON] et al. reported that 24 compounds (OAV > 1) were identified as important compounds and were contributors to the overall aroma of Laoshan green teas [26]. [PERSON] reported that the compounds with OAV > 1 were 29 in green tea, 31 in red tea, and 29 in flower tea. Ten compounds in green tea showed green odor, five \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Compound**} & \multicolumn{2}{c}{**Ci**} & \multirow{2}{*}{**OAV**} & \multirow{2}{*}{**\%**} & \multicolumn{6}{c}{**OAV-Splitting of Odor Characteristic**} \\ \cline{4-9}  & & & & & **Woody** & & **Floral** & **Burnt** & **Green** & **Fruity** & **Fatty** \\ \hline \(\beta\)-Ionone & 0.24 \(\pm\) 0.01 & 34.29 & 61.25 & 17.14 & 10.29 & 6.86 & 0 & 0 & 0 \\
6-Methyl-5-hepten-2-one & 0.32 \(\pm\) 0.03 & 6.40 & 11.43 & 0 & 4.48 & 0 & 0 & 1.92 & 0 \\ (\(E\),\(E\))-2-4-Heptadienal & 0.28 \(\pm\) 0.01 & 5.71 & 10.20 & 0 & 0 & 0 & 0 & 0 & 5.71 \\
1-Pentanol & 0.24 \(\pm\) 0.02 & 1.60 & 2.86 & 0 & 0 & 0 & 0 & 0 & 1.6 \\
1-Penten-3-ol & 0.57 \(\pm\) 0.02 & 1.59 & 2.84 & 0 & 0 & 0.64 & 0.32 & 0.63 & 0 \\ (\(E\))-Geranylacetone & 0.27 \(\pm\) 0.02 & 1.45 & 2.59 & 0 & 1.30 & 0 & 0 & 0 & 0.15 \\ Acetic acid & 7.61 \(\pm\) 0.25 & 1.38 & 2.47 & 0 & 0 & 0 & 0 & 0.14 & 1.24 \\ Hexanal & 0.65 \(\pm\) 0.07 & 1.36 & 2.43 & 0.14 & 0 & 0 & 0.13 & 0.27 & 0.82 \\ Epoxydihydromalool & 0.56 \(\pm\) 0.01 & 1.12 & 2.00 & 1.09 & 0 & 0 & 0 & 0 & 0.03 \\ Inalool & 0.54 \(\pm\) 0.04 & 1.08 & 1.93 & 0 & 1.08 & 0 & 0 & 0 & 0 \\ Total & 11.28 & 55.98 * & & 18.37 & 17.15 & 7.50 & 0.45 & 2.96 & 9.55 \\ \% ** & & & 32.81 & 30.64 & 13.40 & 0.80 & 5.29 & 17.06 \\ \hline \hline \end{tabular} Note: OAVi = Ci/Ti, where Ci is the content of compound i (ng kg\({}^{-1}\)), and Ti is the threshold value of compound i (ng kg\({}^{-1}\)). * OAVt = DAVi. ** \% is proportion of the each odor OAV accounting for OAVt.  
\end{table} 
Table 5: The content, OAVi and OAV-splitting of key aroma compounds in dark tea. compounds in red tea showed baking odor, and 23 compounds and 19 compounds in flower tea showed fruit and floral odors [27]. However, the OAVt of tea can only compare the difference of aroma intensity between tea samples, but can not distinguish the different aroma types, as well as the intensity of various odors. For example, green odor is the most characteristic odor of green tea, no matter what green tea samples. Almost all red tea worldwide has a strong fruity odor. Therefore, the OAVt of tea tells us nothing about the characteristic odor of tea. Currently, when people are discussing about tea fragrance such as 'the tea aroma of A is much intense than that of B', and 'the fruity odor of No 1 tea sample is better than that of No 2', how much is that'much intense' and 'better than'? Tea aroma is a complex of various odors such as woody, floral, burnt, green, fruity, and fatty. We need to split the OAVt of tea into various odors and then find the combination of those odors and the dominant odors.