## 2 Results
### Volatile Compound Profiles in Granny Smith and Jonagold Apples  
Aroma is an essential sensorial property, which determined by the volatile compounds. In the present study, a total of 35 volatile compounds were identified in Granny Smith and Jonagold apples, including 20 esters, 4 alcohols, 8 aldehydes, 1 ketone, 1 phenylpropene and 1 terpenoid (Table 2). Aldehydes, occupying 87.20% of the total volatiles (56.14 \(\mathrm{\SIUnitSymbolMicro g}\)/kg FW), were the most abundant type of volatile compounds contributing to the apple aroma in Granny Smith, following by alcohols (4.29% of the total volatiles; 2.76 \(\mathrm{\SIUnitSymbolMicro g}\)/kg FW) and esters (3.20% of the total volatiles; 2.06 \(\mathrm{\SIUnitSymbolMicro g}\)/kg FW) (Figure 2a; Table S2). By contrast, the main types of volatile compounds in Jonagold were esters (63.00% of the total volatiles; 1333.35 \(\mathrm{\SIUnitSymbolMicro g}\)/kg FW), followed by phenylpropene (25.05% of the total volatiles; 530.16 \(\mathrm{\SIUnitSymbolMicro g}\)/kg FW) and aldehydes (5.73% of the total volatiles; 121.27 \(\mathrm{\SIUnitSymbolMicro g}\)/kg FW) (Figure 2b; Table S2). The apple variety of Granny Smith contained only 16 kinds of volatile compounds, while Jonagold had 31 kinds of volatiles (Table 2). Moreover, 12 volatile compounds were common to the two apple varieties. Among those volatiles, the con \begin{table}
\begin{tabular}{c c c} \hline \hline
**Trait** & **Granny Smith** & **Jonagold** \\ \hline Fresh weight (g) & \(205\pm 15\) & \(240\pm 18\) \\ Height (mm) & \(50.05\pm 1.23\) & \(56.20\pm 1.85\) \\ Diameter (mm) & \(57.80\pm 2.10\) & \(61.55\pm 2.35\) \\ L* value & \(63.52\pm 0.65\) & \(58.62\pm 1.67\) \\ a* value & \(-17.62\pm 1.85\) & \(13.38\pm 2.30\) \\ b* value & \(37.95\pm 1.52\) & \(29.13\pm 2.58\) \\ TSS (\({}^{\circ}\)Brix) & \(13.7\pm 0.2\) & \(14.2\pm 0.2\) \\ TA (\%) & \(0.40\pm 0.04\) & \(0.32\pm 0.03\) \\ Firmness (kg/cm\({}^{2}\)) & \(7.05\pm 0.15\) & \(6.58\pm 0.12\) \\ Internal ethylene (\(\mu\)L/L) & \(5\pm 1\) & \(62\pm 8\) \\ CO\({}_{2}\) production (\(\mu\)mol/kg\(\cdot\)s) & \(70\pm 8\) & \(48\pm 5\) \\ \hline \hline \end{tabular} Values are means \(\pm\) standard deviation; TSS—total soluble solid; TA—titratable acidity.  
\end{table} 
Table 1: Physiological traits of Granny Smith and Jonagold apples. Figure 1: Phenotypes of Granny Smith and Jonagold apples. (**a–c**) Phenotype of the Granny Smith apple. (**d–f**) Phenotype of the Jonagold apple. tents of hexyl acetate, hexyl butanoate and hexyl 2-methylbutyrate in the Granny Smith apple were 1.25, 0.35 and 0.46 \(\upmu\)g/kg FW, respectively, lower than that of 885.38, 27.19 and 31.95 \(\upmu\)g/kg FW in the Jonagold apple. Furthermore, volatiles such as 1-hexanol, hexanal and (_E_)-2-hexenal showed lower contents in Granny Smith than that in Jonagold (Table 2). Additionally, compared to the Granny Smith, Jonagold had higher contents of estragole (530.16 \(\upmu\)g/kg FW) and \(\alpha\)-farnesene (31.15 \(\upmu\)g/kg FW). In comparison with the volatiles detected in these two apple varieties, four volatile compounds were unique to the Granny Smith apple, including 2-hexyn-1-ol, (_Z_)-3-hexenal, (_Z_)-2-heptenal and 1-octen-3-one. There were 19 volatile compounds unique to the Jonagold apple, such as butyl acetate, 2-methylbutyl acetate, 1-butanol and (_E_)-2-decenal (Table 2).