# Characterization of Volatile Substances in Pu-erh Tea (Raw Tea) at Different Storage Times
## 3 Results and Analysis
### Differences and Characterization of Volatile Substances in Different Groups
**} & \multirow{2}{*}{**Component Name**} & \multicolumn{2}{c}{**QT**} & \multicolumn{11}{c}{**ROAV**} & \multicolumn{11}{c}{**F12**} & \multicolumn{1}{c}{**F13**} & \multicolumn{1}{c}{**F14**} & \multicolumn{1}{c}{**F15**} & \multicolumn{1}{c}{**F16**} & \multicolumn{1}{c}{**F17**} & \multicolumn{1}{c}{**F18**} & \multicolumn{1}{c}{**F19**} & \multicolumn{1}{c}{**F19**} & \multicolumn{1}{c}{**F12**} & \multicolumn{1}{c}{**F13**} & \multicolumn{1}{c}{**F14**} \\ \hline
31 & Benner  
To further determine the key aromatic compounds of different groups, the Variable Importance in Projection (VIP) method was applied to quantify the impact of each volatile compound on the classification of the samples. The VIP value effectively reflects the importance of each volatile substance in the model. It is commonly recognized that when the VIP \(\geq\) 1, the volatile substance significantly influences the classification result. In groups A1, A2, A3, and A4, there are 18, 15, 17, and 15 compounds, respectively, with VIP \(\geq\) 1. These compounds make significant contributions to the differentiation of samples into different groups (Figure 5). As shown in Figure 5, there were 18 key volatiles in Group A1 that satisfied VIP \(\geq\) 1. Among them, linalool, trans-linalool oxide (furanoid), and decanal showed floral and fruity aroma [29; 30]; Cedrenol, 2,2,6-trimethyl-Cyclohexanone showed a fruity aroma [31; 32; 33]; 3,7-dimethyl-1,5,7-Octatrien-3-ol showed a clean and fruity aroma [34; 35; 36]; 2-Nonen-1-ol showed a green aroma; benzaldehyde showed a nutty, fruity, and burnt aroma [37]; 2-[(2R,5S)-5-ethenyl-5-methyltetrahydrofuran-2-yl]propan-2-ol had a floral aroma [38]; (+/-)-theaspirane had a honey aroma. Combined with the results of the sensory evaluation, Group A1 showed a fruity/ floral aroma, so these substances are the key volatile for the formation of the fruity/floral aroma. There were 15 key volatiles of Group A2 that satisfied VIP \(\geq\) 1. Among them, cis-\(\beta\)-Ocimene is floral and fruity [39]; 2-ethyl-Furan has a caramelized aroma; benzaldehyde has a nutty, fruity, and caramelized aroma; limonene, cedrenol, 2,2,6-trimethyl-Cyclohexanone has a fruity aroma; hexanal has a fatty aroma; 3,7-dimethyl-1,5,7-Octatrien-3-ol has a clean and fruity aroma; camphene has a floral aroma; cis-\(\beta\)-Ocimene has a floral aroma; o-Cymene has a smoky and woody aroma; and 1-methyl-4-(1-methylethenyl)-Benzene has a fruity, woody odor [40]. Combined with the results of the sensory evaluation, Group A2 was found to have a smoky aroma, so these substances are the key volatile for the formation of smoke aroma. Figure 5: (**A**): VIP score of volatile substances in group A1 (VIP \(\geq\) 1, \(p\) < 0.05); (**B**): VIP score of volatile substances in group A2 (VIP \(\geq\) 1, \(p\) < 0.05); (**C**): VIP score of volatile substances in group A3 (VIP \(\geq\) 1, \(p\) < 0.05); (**D**): VIP score of volatile substances in group A4. (VIP \(\geq\) 1, \(p\) < 0.05). There were 17 key volatiles in Group A3 that satisfied VIP \(\geq\) 1. Among them, 2-methyl-Cyclopentanol showed a fresh and fruity aroma; linalool and \(\alpha\)-Terpinene showed a fruity/floral aroma; 1-methyl-4-(1-methyllytidine)-Cyclohexene showed a woody aroma; hexanal showed a fatty aroma; limonene, trans-\(\beta\)-Ocimene, and \(\gamma\)-Terpinene showed a fruity aroma; benzaldehyde showed a nutty, fruity, and caramelized aroma; (E,E)-2,4-Heptadienal, trans-linalool oxide (furan) showed a fresh and fat aroma [41; 42]; and o-Cymene showed a woody, smoky aroma. Combined with the results of the sensory evaluation, Group A3 was characterized by a fragrance aroma, so these substances are the key volatile for the formation of a fragrance aroma. There were 15 key volatiles in Group A4 that satisfied VIP \(\geq\) 1. Among them, 2-Nonen-1-ol and 2-{(2R,5S)-5-ethenyl-5-methyltetrahydroofuran-2-yl}propan-2-ol showed a fresh aroma; octanal showed a fragrance and fruity aroma; benzaldehyde has a nutty, fruity, and smoky aroma.