## 3 Results and Discussion
### Key Odorants in XYMJ Green Teas  
The contribution of a particular volatile compound to the global aroma of XYMJ green teas depends on not only its content, but also on its odor activity value (OAV). It is generally considered that the compounds with an OAV \(\geq 1\) are great contributors to the aroma characteristics [21]. The higher the OAV of compounds is, the greater the contribution is. As listed in Table 3, a total of 15 volatile compounds with mean OAV \(>1\) were considered as the key odorants in the XYMJ green teas. The highest OAV of 2195.05 was calculated for the violet-like smelling trans-\(\beta\)-ionone followed by decanal (OAV = 57.94),  
Figure 5: Various change trends of the hydrocarbons in XYMJ green teas. All data are expressed as mean \(\pm\) S.D. (\(n=3\)). nonanal (OAV = 30.96), dimethyl sulfide (OAV = 19.53), linalool (OAV = 15.81), geraniol (14.37) and naphthalene (OAV = 10.34). The OAV of geraniol in XYMJ spring teas was higher (\(p<0.05\)) than XYMJ autumn teas. (Z)-3-Hexenyl hexanoate, 1-octen-3-ol, benzaldehyde, cis-nerolidol, heptanal, hexanal, \(\beta\)-cyclocitral and 2,3-octanedione presented OAVs (10 \(<\) OAV \(>\) 1). Compared to the XYMJ spring teas, the OAVs of (Z)-3-hexenyl hexanoate, benzaldehyde, heptanal and hexanal were lower (\(p<0.05\)) in XYMJ autumn teas. Thus, these compounds mentioned above were considered to be the major contributors to the aroma of the XYMJ green teas. Mainly derived from the thermal degradation of \(\beta\)-carotene during the green tea manufacturing process, \(\beta\)-ionone with low odor threshold was considered the most important key odor based on the OAV calculation. \(\beta\)-Ionone is an essential volatile compound for the tea aroma formation and has been identified as a significant contributor to the tea aroma, including green tea [18; 19; 35], white tea [36; 37], yellow tea [38], oolong tea [39; 40], black tea [41; 42] and dark tea [43; 44; 45]. The aldehydes, derived from the lipid oxidation, play an important role on the entire odor [24]. The OAVs of floral-fruity aldehydes (nonanal and decanal) were approximately 20-40 times higher than that of grassy or chestnut-like aldehydes (hexanal and heptanal), which would be helpful to the aroma quality of XYMJ green teas. Dimethyl sulfide is one of the common aroma compounds in green tea, and it could be formed from its precursor methyl methionine sulfonium salt upon the thermal decomposition [23]. It has been confirmed by the aroma recombination experiment that dimethyl sulfide had an important contribution to cooked corn-like aroma of green teas made by tea cultivar '_Zhonghuang 1_' [20]. Dimethyl sulfide showed a high flavor dilution factor in high-grade matcha and had some connection with the quality of matcha [46]. Among the alcohol compounds, terpenic alcohols, including linalool, geraniol and cis-nerolidol, are the dominant odorants for the XYMJ green teas. Due to their high OAVs and floral-fruity aroma notes, the terpenic alcohols are beneficial to the aroma of the excellent-quality green tea. With pungent naphthyl odor, naphthalene was identified as the key odorants responsible for the chestnut-like aroma quality of green teas [19]. (Z)-3-hexenyl hexanoate was found to be not only abundant in its content, but also prominent in OAV (2.62). Formed from linoleic acid, 1-octen-3-ol (OAV = 2.06) presents a mushroom-like odor and was also identified as one of the key aroma compounds of Longjing tea [23; 46]. Benzaldehyde (OAV = 2.00) is described as almond-like smell and \(\beta\)-cyclocitral (OAV = 1.25) contributes a fruity aroma.