## 3 Results and Discussion
### The Relationship between Aroma Attributes and Key Aroma Substances  
The correlations between 27 key aroma components (OAV > 1) and eight aroma sensory attributes of green huajiao samples were explained by the PLSR model [41]. The PLSR model was used to formulate a mathematical model to determine the relationship between the aroma attributes and the aroma components to identify the key aromas contributing to the aroma sensory attributes [37]. The OAVs of the key aroma components were used as independent variables and the rank sums of the aroma attribute as the dependent variables. As shown in Figure 7, the PLSR model presented two significant principal components that explained a total of 92.46% of the x variables. Most of the key aroma components and aroma sensory attributes of the green huajiao samples were located between internal and external ellipses at \(r^{2}\) = 0.5 and \(r^{2}\) = 1, respectively, indicating that the model could explain these variables well, and most of the characteristic aroma components correlated differently with the aroma attributes of huajiao. Eight aroma sensory attributes were distributed on the left and right side of the x-axis and showed a high correlation with the 27 aroma compounds. The sensory attributes floral, pungent and herbal are very close to each other and appeared on the upper right side of the coordinate axis, which showed a strong positive correlation with \(\alpha\)-pinene (L1), sabinene (L2), \(\beta\)-pinene (L3), mycrene (L4), p-cymene (L7), linalool (L14) and terpinen-4-ol (L17). This is consistent with the previous report, which showed that L1, L2, L3 and L17 have pungent, herbal, pine oil odors and L4 has a flowery odor. The sweet sensory attributes are on the right side of the x-axis and show a strong positive correlation with the sweet odor of ocimene (L10). The sensory attributes minty and green are very close to each other at the bottom left of the coordinate axis. They showed a strong positive correlation with citronellal (L16) and a medium correlation with \(\alpha\)-terpineol (L18), which is reported to have the odors of cucumber and mint, respectively. The sensory attributes citrus and lemony were on the left side of the x-axis and showed a strong positive correlation with \(\alpha\)-terpineol (L8), which is reported to have the odors of lemon and citrus. Figure 6: Clustering heatmap of OAVs of green huajiao Samples. The different aroma compounds of seven green huajiao samples were further analyzed using variable importance in projection (VIP). The VIP represented the contribution of the aroma compound to the differences between the huajiao samples, and substances with a VIP \(>\)1 were considered to make a key contribution to the differences between the samples [41]. As shown in Figure 8, 15 aroma compounds with VIP values greater than 1 (\(p<0.05\)) were finally obtained, including \(\alpha\)-pinene (L1), sabinene (L2), \(\beta\)-pinene (L3), myr scene (L4), phellandrene (L5), terpionlee (L6), limonene (L8), ocimene (L10), \(\gamma\)-terpinene (L11), linalool (L14), citronellal (L16), terpinen-4-ol (L17), \(\alpha\)-terpineol (18), tetradecane (L24) and caryophyllene oxide (L27). Myrcene was identified as a key aroma compound to distinguish the cultivar and growing region of huajiao samples in a previous report [17]. In addition, linalool (L14), limonene (L8) and sabinene (L2) were also used to distinguish the growing area and cultivar [33; 36]. These reports were consistent with the results of this study. Figure 8: VIPs of the green huajiao samples. Figure 7: Bipolar diagram of key aroma compounds and aroma sensory attributes. As shown in Figure 7, seven huajiao samples from Sichuan and Chongqing regions were divided into three groups. G6 from Chongqing was at the lower end of the y-axis had a medium-high aroma intensity of green, minty and sweet. Ocimene (L10), citronellal (16) and \(\alpha\)-terpineol (18) were the key characteristic aroma compounds that distinguished the huajiao samples of Sichuan Province.