## 3 Results and Discussion
### Analysis of Key VOCs in Eight Pear Varieties Based on OPLS-DA and HCA  
OPLS-DA is a multivariate calibration method [36] that maximizes intergroup differentiation and facilitates the search for differential metabolites [37]. In order to investigate the significantly different VOCs of different pear varieties at different shelf life, 160 VOCs of the eight pear varieties were used as dependent variables, and based on the content of aroma components of the eight pear varieties at different shelf life as independent variables, the eight pear varieties could be clearly classified into six groups by OPLS-DA and HCA (Figure 4A,B). Group 1 consisted of Nanguoli, group 2 consisted of Ruanerli, group 3 consisted of Louis and Cure, group 4 consisted of Korla pear, group 5 consisted of Jingbaili, and group 6 consisted of Yali and Hanhongli, to achieve the effective differentiation between  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Cubicown**} & **Shelf** & **Extens** & **Alcohols** & **Alcohols** & **Alcohols** & **Kansas** & **Aalois** & **Ilybanealione** & **Odense** \\  & **Life** & **Type** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** \\  & **Type** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** \\  & **Type** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** \\  & **Type** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions** & **Constructions**  
the crisp-flesh pear and soft-flesh pear samples, indicating significant differences in the composition of VOCs between crispy and soft-flesh pears. After 200 replacement tests, the replacement test model R2 was 0.55, Q2 was \(-\)0.842, and the intersection point of the Q2 regression line and the vertical axis was less than 0 (Figure 4C), indicating that the discriminant model had a good explanatory ability and did not overfit, and the model validation was effective [38].  
Variable importance in projection (VIP) in OPLS-DA represents the effect of differences between the corresponding metabolites on the classification and identification of each group of samples in the model, and it is generally accepted that there are significant differences in metabolites with VIP \(>\) 1 and \(p\) \(<\) 0.05 [39]. According to the OPLS-DA model, 32 differential aroma components with VIP \(>\)1 were screened (Figure 4D), and combined with \(p\) \(<\) 0.05 (Table S1), a total of 31 differential VOCs were screened. Among them, there were 13 esters, 7 alcohols, 5 aldehydes, 3 ketones, 2 hydrocarbons and 1 other compound, which were Ethyl caproate, Hexanal, (E,E)-\(\alpha\)-Farresene, trans-\(\alpha\),\(\alpha\),5-Trimethyl-5-ethernyltetrahydro-2-furanmethanol, (E)-2-Hexanal, Ethyl butanoate, Ethyl (E,Z)-2,4-decadienoate, (E)-1-(2,6,6-Trimethyl-1,3-cyclohexadien-1-yl)-2-buten-1-one, (E)-2-Heptenal, 1-Hexanol, Butyl acetate, (E)-3-Hexenol acetate, Methyl caproate, (Z,E)-methyl 2,4-decadienoate, trans-3-Hexenol, \(\alpha\)-Terpineol, (E)-2-Octenal, DL-2-Methylbutanol, 6-Methyl-5-heptene-2-one, Methyl butanoate, 1-Hepten-3-one, 1-Octen-3-ol, Ethyl 3-hydroxyhexanoate, Ethyl 2-methylbutanoate, Ethyl (E)-2-octenoate, Linalool, (Z,E)-\(\alpha\)-Farresene, (E)-2-Decenal, Hexyl acetate, Phenethyl acetate and (E)-2-Hexen-1-ol.