# Characterization of the Key Aroma Compounds in Different Aroma Types of Chinese Yellow Tea
## 3 Results and Discussion
### Key Aroma Compounds in Different Aroma Types of Yellow Tea
Among these discriminative aroma compounds, eight, fourteen, seven, and eighteen aroma compounds with the highest levels in the floral fragrance, high-fired fragrance, fresh fragrance, and corn-like fragrance types of yellow teas, respectively. High contents of these discriminative aroma compounds might play an important role in the formation of different aroma characteristics of yellow tea. Therefore, these discriminative aroma compounds were recognized as key aroma compounds in different aroma types of yellow tea. In the floral fragrance types of yellow tea, (\(Z\))-citral, citral, jasanone, (\(E\))-linaloal oxide (furanoid), decanal, geraniol, (\(E\))-2-octen-1-ol, and safranal were identified as the key aroma compounds. Among them, (\(Z\))-citral and citral with 'citrus' odor have been reported to be responsible for the formation of strongly fruity fragrance in lemon basil and hops [25; 26]. \(\epsilon\)-Linaloal oxide (furanoid) possesses a 'floral' odor and has been widely detected in yellow tea, green tea, black tea, and oolong tea. It has been considered as the important compound that contributes to 'floral' aroma formation in tea products [1; 6; 8; 27; 28]. In addition, as a vital odoriferous compound of honey, safranal has been regarded as an important aromaticity compound because of its 'ripe fruit' and 'honey' odor [6; 14; 16; 29]. (\(E\))-2-Octen-1-ol emits a 'grassy' odor and has been considered as an aroma-active compound responsible for the 'green' aroma characteristics formation of asam sunti [30]. In high-fired fragrance type of yellow tea, 3,5-diethyl-2-methylpyrazine, 2-methyl-5-ethylpyrazine, 2,3-diethyl-5-methylpyrazine, 2,5-dimethyl-3-ethylpyrazine, o-tolunitrile, dextro-limonene, \(\alpha\)-ionene, acetophenone, methyl anthranilate, benzyl alcohol, methyl benzoate, 1,2-dihydro-1,1,6-trimethylnaphthalene, methyl salicate, and para-xylene were identified as the key aroma compounds. Pyrazines, usually possess a 'roasted' attribute generated by heat treatment and exist abundantly in a large number of cooked, roasted, and toasted foods. For example, 3,5-diethyl-2-methylpyrazine, 2,3-diethyl-5-methylpyrazine, 2-methyl-5-ethylpyrazine, and 2,5-dimethyl-3-ethylpyrazine produce a 'roasted hazelnut' note, and have are considered as important contributors for the 'roasted' odor formation of  
Figure 3: Heatmap of the discriminatory aroma compounds in the different aroma types of yellow teas. yellow tea, green tea, coffee, and coco [7; 8; 9; 31]. In addition, para-xylene with a 'roasted' attribute was identified as an aroma compound in yellow tea. This has long been considered to be a key characteristic aroma marker for the roasting process of oolong tea [7; 32]. In addition, methyl anthranilate has a typical 'grape juice' odor that can improve the 'floral and fruity' aroma characteristics in many kinds of tea [6; 8; 12; 33]. In the fresh fragrance type of yellow tea, indole, phenethyl alcohol, (_E_)-3-hexen-1-ol, \(\alpha\)-terpineol, ethyl hexanoate, ethyl nonanoate, and ethyl octanoate were identified as the key aroma compounds. Esters are well-known aroma compounds that play an important role in the properties of beverages. Ethyl nonanoate, ethyl hexanoate, and ethyl octanoate are the representative ester compounds that can provide 'floral', 'fruity', and 'waxy' odors [6; 34]. For example, ethyl hexanoate has been identified as an important aroma compound in oolong tea with a 'pineapple' odor, which contributes to the'sweet fruit' aroma formation of special aroma characteristics of black tea [23; 35]. Ethyl nonanoate has been considered as a potential aroma-active compound in fruits, and it also contributes to the formation of 'rose-like' aroma in black tea [35; 36]. In addition, (_E_)-3-Hexen-1-ol has a 'green' note and has been reported to contribute to the formation of 'green', 'grass', and 'fresh' odors of black tea and oolong tea [16; 23].