## 3 Results and Discussion
### Analysis of Differences in the Composition of Total Volatile Compounds  
It was previously found that esters were the VOCs with the highest number of compounds in pear fruits, with alcohols second only to esters [6; 9]. Similar results were obtained in this study. A total of 160 VOCs were detected from Korla pear, Yali, Hanhongli, Nanguoli, Jingbaili, Ruanerli, Cure and Louis during the whole shelf life, and the detected VOCs were classified into seven major categories according to the difference of the main functional groups of the compounds, including 61 esters, 39 alcohols, 18 aldehydes, 12 ketones, 7 acids, 13 hydrocarbons, and 10 other compounds, as seen in Figure 1A. Nanguoli and Jingbaili had the most types of VOCs, namely, 81 kinds, whereas Cure had the fewest types of VOCs, namely, 41 kinds. Yali, Hanhongli, Nanguoli, Jingbaili and Ruanerli had the most types of esters, Cure and Louis had the most types of alcohol, Korla pear had the most alcohol and aldehydes, and these eight pear varieties had fewer ketones, acids, hydrocarbons and other compounds. In addition, only one kind of ester was detected in Cure, and no hydrocarbon was detected in Hanhongli.  
There were significant differences in the content of VOCs among pear varieties, as seen in Figure 1B. The VOC content of the eight pear varieties was ranked as Nanguoli (87.43 mg/kg) > Ruanerli (83.50 mg/kg) > Jingbaili (51.10 mg/kg) > Korla pear (30.62 mg/kg) > Yali (27.79 mg/kg) > Hanhongli (27.21 mg/kg) > Louis (23.77 mg/kg) > Cure (21.69 mg/kg). The relative content of VOCs in the eight pear varieties varied greatly among the varieties. The most VOCs in Ruanerli and Nanguoli were esters, and their relative content was 50.71% and 62.84%, much higher than the content of esters in the rest of the pear varieties. Korla pear, Yali, Jingbaili, Cure and Louis had high levels of aldehydes, with respective relative contents of 71.74%, 38.65%, 38.52%, 47.86% and 44.08%. The highest content of esters (35.07%) was found in Hanhongli among these crispy pears. In conclusion, the types and contents of VOCs in the eight pear varieties were relatively higher for esters, alcohols and aldehydes, compared to ketones, acids, hydrocarbons and other compounds, which were at a lower level. Other researchers found that esters, alcohols and aldehydes  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Cultivars**} & \multirow{2}{*}{**Texture**} & \multicolumn{4}{c}{**Shelf Life**} \\ \cline{3-6}  & & **0 d** & **3 d** & **7 d** & **14 d** & **21 d** \\ \hline Korla pear & Crisp & 11.98 \(\pm\) 0.33 de & 12.87 \(\pm\) 0.44 c & 12.99 \(\pm\) 0.56 cd & 11.87 \(\pm\) 0.72 e & 12.70 \(\pm\) 0.27 d \\ Yali & Crisp & 10.43 \(\pm\) 0.25 f & 10.47 \(\pm\) 0.34 e & 10.21 \(\pm\) 0.65 f & 10.44 \(\pm\) 0.55 f & 10.32 \(\pm\) 0.36 f \\ Hanhongli & Crisp & 11.61 \(\pm\) 0.50 e & 12.11 \(\pm\) 0.42 d & 12.37 \(\pm\) 0.95 d & 12.59 \(\pm\) 0.45 d & 12.25 \(\pm\) 0.42 d \\ Nanguoli & Soft & 15.23 \(\pm\) 0.54 a & 16.86 \(\pm\) 1.26 a & 17.04 \(\pm\) 1.12 a & 18.02 \(\pm\) 1.06 a & 17.71 \(\pm\) 1.04 a \\ Jingbaili & Soft & 12.30 \(\pm\) 1.46 cd & 13.09 \(\pm\) 0.53 c & 13.62 \(\pm\) 0.83 bc & 14.25 \(\pm\) 0.90 b & 14.54 \(\pm\) 0.86 b \\ Ruanerli & Soft & 14.06 \(\pm\) 0.57 b & 14.28 \(\pm\) 0.39 b & 14.16 \(\pm\) 0.53 b & 13.15 \(\pm\) 0.75 cd & 12.53 \(\pm\) 1.34 d \\ Cure & Soft & 11.49 \(\pm\) 0.25 e & 11.74 \(\pm\) 0.57 d & 10.94 \(\pm\) 1.13 e & 12.55 \(\pm\) 0.67 d & 11.08 \(\pm\) 0.39 e \\ Louis & Soft & 12.79 \(\pm\) 0.41 c & 13.13 \(\pm\) 0.47 c & 13.83 \(\pm\) 0.35 b & 13.44 \(\pm\) 0.70 c & 13.82 \(\pm\) 0.51 c \\ \hline \hline \end{tabular} Note: Values represent mean \(\pm\) standard deviation (SD) (\(n=10\)). Significant differences in results were indicated by different letters (a > b > c > d > e > f).  
\end{table}
Table 1: SSC changes of eight pear varieties during shelf life.  
were the major VOCs in the fruits of 202 mature pear varieties [29]. Esters, alcohols and aldehydes were equally dominant in 33 _P. ussuriensis_ cultivars [22].