## 3 Discussion  
Green teas have various types of scents, which are attributed to their different volatile profiles. There were 68 volatiles annotated in all the green teas, which was comparable to the number of volatiles reported in Biluochun green tea [10]. Terpenoid volatiles, such as C6 aldehydes, alcohols, and their esters, are important contributors to the green aroma of fruits and vegetables [21], which are also regarded as the most important odorants in tea leaves due to their high contents and low thresholds [22]. In our study, alcohols were the major volatile compounds present in all the teas samples prepared from different cultivars, which is consistent with previous studies [2; 23]. Alcohol compounds were the important compounds for discriminating 'Chunyu2' and 'Jinguanyin' green teas with floral fragrance from other green teas, while ester compounds were the key compounds for discriminating 'Chunyu2' green tea from other green teas. 3,7-Dimethylocta-1,6-dien-3-ol and the oxides [e.g., 6-ethenyl-2,2,6-trimethyloxan-3-ol, 2-[(25,55)-5-ethenyl-5-methyloxolan-2-yl]propan-2-ol], (2_E_)-3,7-dimethylocta-2,6-dien-1-ol, phenylmethanol, and 2-phenylethanol importantly contributed to the floral aroma of oolog tea and black tea [2; 9; 16]. Dodecan-1-ol and 2-(4-methylcyclohex-3-en-1-yl)propan-2-ol have floral smell [24; 25]. (_E_)-Hex-2-en-1-ol, (_Z_)-hex-3-en-1-ol are related to green and grassy odor [26], and heptan-2-ol gives a citrus aroma [27]. The abundant presence of floral odorants in 'Chunyu2' green tea, including 3,7-dimethylocta-1,6-dien-3-ol and the oxides, dodecan-1-ol and 2-phenylethanol, together  
Figure 6: Correlation network of the top ten volatiles in green tea and black tea correlated with the shared volatiles in three types of tea samples. Alcohol compounds (blue nodes), aldehyde compounds (red nodes), ketone compounds (light green nodes), ester compounds (orange nodes), and miscellaneous compounds (light yellow nodes). The correlation analysis of the contents of the key volatiles in different tea samples was conducted by the Cytoscape software (version 3.8.0) ([[https://cytoscape.org/](https://cytoscape.org/)]([https://cytoscape.org/](https://cytoscape.org/)), accessed on: 23 March 2021). A significant correlation was presented based on the statistical test with a robust cutoff (_p_-value \(<\) 0.05), with a black line indicating a positive correlation and a blue line indicating a negative correlation. The absolute value of the correlation coefficient increased from 0.515 to 0.984 as the line width was increased. The number of replicates is equal to 3.  
with the green and grassy odorants such as (_E_)-hex-2-en-1-ol, (_Z_)-hex-3-en-1-ol and heptan-2-ol, led to its orchid-like fragrance. By contrast, the high levels of rose odorants such as (_2E_)-3,7-dimethylocta-2,6-dien-1-ol and phenylmethanol but low contents of green and grassy odorants formed the rose fragrance of 'Jinguanyin' green tea. The aroma characteristics of black tea are quite different from green tea, which generally has a sweet aroma. 'Jinguanyin' and 'Chunyuz' black teas with floral aroma were discriminated from other black teas based on the composition of alcohols, which was the same as green teas. Furthermore, 'Jinguanyin' black tea was distinguished from other black teas based on the compositions of aldehydes, ketones, and esters. Odorants such as (_2E_)-3,7-dimethylocta-2,6-dien-1-ol, (_1S_,_2R_,_5S_,_7R_,_8R_)-2,6,6,8-tetramethyltricylylcq[5.3.1.01,5]undecan-8-ol, (_6E_)-3,7,11-trimethyldodeca-1,6,10-trien-3-ol, and dodecan-1-ol are associated with rose-like floral aroma, which were considered as important contributors to the floral fragrance of 'Jinguanyin' black tea. Moreover, many aldehydes, ketones, and esters have unique fruity or floral aromas [10,28]. The abundant presence of esters and aldehydes might be related to the long-lasting floral and sweet fragrance of 'Jinguanyin' black tea that was distinguished from the weaker floral aroma of 'Chunyuz' black tea as well as the rose odor of 'Jinguanyin' green tea.