## 3 Results and Discussion
### Analysis of Differential VOCs in the Flesh of Eight Pear Varieties  
The content of differential aroma components had an important contribution to the formation of the aroma characteristics of each variety, and the clustering heat map could clearly distinguish the higher content of differential VOCs in each texture, making the comparison of the content of differential VOCs in different pear varieties more obvious (Figure 6). Figure 5: PCA of differential VOCs in pear varieties with different flesh textures. Esters. In terms of type and content, esters with a fruity flavor are the main VOCs in pears [10]. The ester content in the soft-flesh pears was larger and more variable than in the crisp-flesh pears. Jingbaili had a high concentration of Methyl butanoate and Methyl caproate. Both compounds exhibited an increasing and then decreasing trend with the prolongation of shelf life, with the highest content detected on the 14 d of shelf-life. Throughout the shelf life, Ruanerli and Nanguoli had high levels of Hexyl acetate, Butyl acetate, Ethyl caproate, Ethyl butanoate and Methyl caproate. Except for Butyl acetate, the other four compounds showed an increasing and then decreasing trend in Ruanerli, and an increasing and then decreasing trend in Nanguoli. Nanguoli had high content of Ethyl 3-hydroxyhexanoate, Ethyl 2-methylbutanoate and Ethyl (E)-2-ocenoate, all of which were detected in the highest content at the 21 d of shelf life. (Z,E)-methyl-2,4-decadienoate and Ethyl (E,Z)-2,4-decadienoate were two esters with a pear-like odor [6], which were considered to be characteristic compounds of _P. communis_[9]. High levels of (Z,E)-methyl-2,4-decadienoate, Ethyl (E,Z)-2,4-decadienoate were also detected in Louis at the 21 d of shelf life. Nanguoli at the 14 and 21 d of shelf life had high concentrations of Ethyl (E,Z)-2,4-decadienoate. Alcohols and aldehydes. C6 compounds (C6 alcohols and C6 aldehydes) are the representatives of the green aroma type of compounds, which contribute the green aroma odor to the fruits [42]. The volatiles in Yali, Hanhongli, Korla Pear, Jingbaili, Ruanerli and Nanguoli had higher levels of 1-Hexanol, Hexanal and (E)-2-Hexanal, and lower levels in Louis and Cure, as seen in Figure 6.  
With the prolongation of shelf life, the 1-Hexanol content gradually decreased in Yali, had little change in Jingbaili, and showed the trend of increasing and then decreasing in Hanhongli, Korla pear, Ruanerli and Nanguoli. The Hexanal content showed the trend of increasing and then decreasing in Korla pear, and reached the maximum value in the 14 d of shelf life. Its content in Yali, Hanhongli, Ruanerli and Nanguoli was in a fluctuating state, while Jingbaili showed a trend of first decreasing and then increasing. Except for Yali, which reached the maximum value at the 7 d of shelf life, its values in the other four pear varieties were highest at 0 d of shelf life. (E)-2-Hexanal content in Yali, Hanhongli, Korla pear, Jingbaili and Nanguoli all showed the trend of first increasing and then decreasing with the prolongation of shelf life. Overall, compared with soft-flesh pears, the change in 1-Hexanol content in crisp-flesh pears was greater, while the change in Hexanal and (E)-2-Hexanal content was smaller. Figure 6: Clustering heat map of differential VOCs in eight pear varieties. Yali, Hanhongli, Ruanerli and Nanguoli had a high concentration of (E)-2-Hexen-1-ol. Generally, its content in Yali and Ruanerli decreased gradually as the shelf life extended, while the highest content was detected in Hanhongli and Nanguoli at the 7 d and 3 d of shelf life, respectively, and then showed a decreasing trend. Monoterpene alcohols such aslinal and \(\alpha\)-Terpineol are important aroma and flavor compounds in fruits [43]. Linalool is present in plants mainly as a component of essential oils and is produced by many flowers and spice plants with pleasant floral and citrus aromas [44].