# Characterization of the Key Aroma Compounds in Different Aroma Types of Chinese Yellow Tea
## 3 Results and Discussion
### Relationship between Aroma-Active Compounds and Sensory Attributes  
To explore the relationships between the aroma-active compounds (OAV \(>\) 1) and sensory attributes, a PLS model was established. Two latent variables were included in the PLS model, which represented 86.90% of X-matrix variance (aroma-active compounds) and explained 99.30% of Y-matrix variance (sensory attributes). As shown in Figure 4, the positions of the sensory attributes and aroma-active compounds of yellow tea between the two ellipses indicated that they were well explained by the PLS model. Among these samples, the floral fragrance (H1-H7) and corn-like fragrance types of yellow teas (Y1-Y9) are mainly located on the upper part of PC2. The fresh fragrance type of yellow tea samples (Q1-Q6) are mainly located in the negative region of PC1 and PC2. The high-fired fragrance type yellow tea samples (HG1-HG4) are mainly located in the positive region of PC1 and negative region of PC2. This clearly indicates that tea samples can be divided into four groups according to their aroma types.  
The five attributes ('floral and fruity', 'roasted', 'fresh', 'grassy', and'sweet') that significantly correlated with some aroma-active compounds were located between the inner and outer ellipses. The 'floral and fruity','sweet', and 'roasted' attributes were located on the positive dimension, and the 'fresh' and 'green' attributes were located on the negative dimension of the first PC1. The floral fragrance and corn-like fragrance types of yellow tea samples were strongly associated with 'floral and fruity' and'sweet' attributes, the high-fired fragrance type of yellow tea was strongly associated with 'roasted' attribute, and the fresh fragrance type of yellow tea was strongly associated with 'fresh' and 'green' attributes. Furthermore, the 'floral and fruity' and'sweet' attributes were positively correlated to l-menthone, heptanal, naphthalene, 2-methylnaphthalene, 1-methylnaphthalene, methyl heptenone, decanal, styrene, safranal, toluene, para-xylene, and acetophenone. A previous study suggested that the 'floral and fruity' attribute was related to the'sweet' attribute in tea [43]. The 'roasted' attribute was positively correlated to methyl anthranilate, 2,3-diethyl-5-methylpyrazine, 2-methyl-5-ethylpyrazine, 2,5-dimethyl-3-ethylpyrazine, and 3,5-diethyl-2-methyl pyrazine. It is well known that the intensity of the 'roasted' attribute mainly depends on the content of pyrazine compounds, which has been confirmed by a previous study [1]. The 'fresh' and 'green' attributes were positively correlated with (\(E\))-3-hexen-1-ol, ethyl hexanoate, ethyl nonanoate, and ethyl octanoate. Previous studies have shown that ethyl esters with low detection thresholds usually exist in large amounts in wine and play a vital role in the formation of fruity aroma characteristics [44]. Meanwhile, it has also been reported that these esters make an important contribution to the fresh aroma characteristics of yellow tea, which differs from green and black teas [6].  
Figure 4: PLS plots for the tea samples, the sensory analysis, and active-aroma volatiles (OAV > 1). VC1: acetophenone; VC6: (E)-3-hexen-1-ol; VC7: 2-methylnaphthalene; VC8: naphthalene; VC9: 1-methylnaphthalene; VC66: 3,5-diethyl-2-methyl pyrazine; VC67: 2,3-diethyl-5-methylpyrazine; VC72: l-menthone; VC76: methyl anthranilate; VC77: 2,5-dimethyl-3-ethylpyrazine; VC78: 2-methyl-5-ethylpyrazine; VC81: ethyl hexanoate; CC83: ethyl nonanoate; VC89: safranal; VC92: decanal; VC93: heptanal; VC94: methyl heptanone; VC95: toluene; VC96: para-xylene; VC97: ethyl octanoate; VC103: styrene.