## 3 Results and Discussion  
### Identification and Quantification of VOCs  
Salt addition was used in a previous study to enhance the dissociation of VOCs [18]. However, browning of pear fruit occurred rapidly and resulted in color changes (Figure S2b) and loss of flavor. In accordance with our previous study, NaCl was mixed with sliced pear (1:1, m/m) before homogenization to prevent browning [20]. As can be seen in Figure S2a, the color of the pear matrix was less intense and prevented browning from developing. In 12 cultivars of pear fruits, a total of 121 VOCs were identified and quantified, including 40 esters, 32 alcohols, 16 aldehydes, 13 alkenes, 11 ketones, 4 acids, and 5 other compounds. The number of VOCs in different pear cultivars varied dramatically and ranged from 13 to 71 (Figure 1a). It was noteworthy that [PERSON] pear had the highest number of VOCs (Figure 2). As shown in Figure 1a, between 32 and 45 different VOCs were detected in Starkrimson, Caiyunhong, Mantianhong, Hanhong, Meirensu, and Nanguo pears, while less than 30 VOCs were found in Zaosu, Yuluxiang, Yunhexue, Yali, and Qiuyue pears. Among them, Hanhong, Qiuyue, Yali, Yuluxiang, and Zaosu are white pears (Table 1). In this study, [PERSON] (71) and Starkrimson (43) pears produced considerably more types of VOCs than did white pears (13-37). Significant differences in amounts of VOCs among pear cultivars were also observed (Figure 1b). Dr. Guyot pear had the highest total content of VOCs (55.65 mg/kg FW, fresh weight), followed by Zaosu (41.77 mg/kg FW). Meanwhile, VOC content in Starkrimson, Mantianhong, and Caiyunhong pears were 10.51 mg/kg FW, 10.64 mg/kg FW, and 12.36 mg/kg FW, respectively. In contrast, the other seven pear cultivars produced a low level of VOCs, with a content of less than 10 mg/kg FW. Aroma is the mixture of VOCs with various compositions and concentrations [24]. In this study, esters, alcohols, and aldehydes were the main groups of VOCs (Figure 1), which were consistent with the findings obtained in accidental pears [11], and Chinese white pears [13]. However, Zaosu pear was characterized as having a high content of alkenes (Figure 1b), a similar characteristic to that found in Fuji apple [20]. It was interesting to note that one of the maternal parents of Zaosu pear is named 'apple-pear' in China. addition, 1-hexanol and 3,5-di-tert-butylphenol were detected in all cultivars with contents of 0.05-3.12 mg/kg FW and 0.02-0.60 mg/kg FW, respectively. Aldehydes. Aldehydes produce a wide range of special flavors and odors, even at trace amounts [26]. These compounds are predominant in the immature fruit, but some aldehydes become imperceptible after ripening [27]. In this study, the number of aldehydes detected in pears was 4-14, while the contents were 0.82-6.96 mg/kg FW. Volatile C6 and C9 aldehydes are important contributors to green, grassy characteristic flavors in pear [11]. Among them, hexanal and 2-hexanal were found in all pears at concentrations of 0.10-4.60 mg/kg FW (Table S1). The compound 2-octenal, with the content of 0.03-0.89 mg/kg FW, was also detectable in all cultivars. Nonanal (C9) provided a strong smell of grease and sweet orange flavor. It is commonly detected in apples [19] and pears [13]. In the present work, nonanal was absent only in Yunhexue pear, and its content was 0.12-0.84 mg/kg FW in the other cultivars. Ketones. Ketones are the main fruity, sweet flavor compounds in fruit. However, they are undetectable in 13 among 33 _Pyrus ussuriensis_ cultivars [13]. In this study, ketones were present in all 12 cultivars, with a total number of 11. There were 8 ketones found in [PERSON] pear. Concentration of ketones was highest in Dr. Guyot (1.96 mg/kg FW), followed by Zaosu (1.72 mg/kg FW), Starkrimson (1.41 mg/kg FW), and Nanguo (1.25 mg/kg FW), whereas the lowest was in Yali pear (0.11 mg/kg FW). With the exception of Qiuyue, damascenone was present in all cultivars, with concentrations ranging from 0.04 to 1.50 mg/kg FW. Alkenes.