## 2 Materials and Methods
### HS-SPME Procedure  
HS-SPME was applied for the extraction and concentration of volatile compounds in apple peels. All the extractions were performed using a divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fibre with a thickness of 50/30 \(\upmu\)m (Supelco, Bellefonte, PA, USA). For the extraction of volatile compounds, 5 g of apple peel was placed into a 50 mL screw-cap headspace vial containing a magnetic stirring rotor and 1 g NaCl spiked with 10 \(\upmu\)L (0.4 mg/mL) 3-nonanone (internal standard). Subsequently, the \begin{table}
\begin{tabular}{c c c c c c} \hline
**No.** & **Cultivar** & **Code** & **SFW (g)** & **TSS (°Brix)** & **TA (\%)** \\ \hline
1 & Royal Gala & RG & \(175\pm 15\) & 12.7 \(\pm\) 0.2 & 0.42 \(\pm\) 0.03 \\
2 & Golden Delicious & GD & \(262\pm 22\) & 13.5 \(\pm\) 0.4 & 0.44 \(\pm\) 0.04 \\
3 & Fuji & FI & \(320\pm 25\) & 13.2 \(\pm\) 0.2 & 0.29 \(\pm\) 0.02 \\
4 & Jonggold & JNG & \(280\pm 20\) & 14.3 \(\pm\) 0.3 & 0.37 \(\pm\) 0.03 \\
5 & Indo & ID & \(350\pm 32\) & 13.8 \(\pm\) 0.2 & 0.13 \(\pm\) 0.01 \\
6 & Orin & OI & \(255\pm 24\) & 14.5 \(\pm\) 0.1 & 0.30 \(\pm\) 0.02 \\
7 & Hanfu & HF & \(285\pm 18\) & 13.5 \(\pm\) 0.2 & 0.36 \(\pm\) 0.02 \\
8 & Jonathan & JNT & \(325\pm 23\) & 14.1 \(\pm\) 0.2 & 0.37 \(\pm\) 0.03 \\
9 & Miyakiji & MYK & \(310\pm 26\) & 14.6 \(\pm\) 0.4 & 0.30 \(\pm\) 0.03 \\
10 & Granny Smith & GS & \(285\pm 18\) & 14.4 \(\pm\) 0.3 & 0.37 \(\pm\) 0.01 \\
11 & Ralls & RL & \(184\pm 12\) & 14.0 \(\pm\) 0.2 & 0.26 \(\pm\) 0.02 \\
12 & Starkrimson & SR & \(275\pm 15\) & 12.3 \(\pm\) 0.1 & 0.28 \(\pm\) 0.02 \\
13 & Huaguan & HG & \(178\pm 12\) & 13.8 \(\pm\) 0.3 & 0.27 \(\pm\) 0.03 \\
14 & Huashuo & HS & \(266\pm 20\) & 13.6 \(\pm\) 0.2 & 0.38 \(\pm\) 0.01 \\
15 & Huayu & HY & \(198\pm 12\) & 13.1 \(\pm\) 0.2 & 0.29 \(\pm\) 0.03 \\
16 & Envy & EV & \(315\pm 24\) & 14.6 \(\pm\) 0.3 & 0.38 \(\pm\) 0.02 \\
17 & Red General & RGL & \(268\pm 17\) & 15.6 \(\pm\) 0.3 & 0.28 \(\pm\) 0.04 \\
18 & Starking & SI & \(290\pm 22\) & 12.9 \(\pm\) 0.2 & 0.32 \(\pm\) 0.03 \\
19 & Jiguan & JG & \(217\pm 13\) & 13.7 \(\pm\) 0.1 & 0.26 \(\pm\) 0.03 \\
20 & Cox Orange & COP & \(256\pm 20\) & 13.2 \(\pm\) 0.3 & 0.36 \(\pm\) 0.02 \\
21 & Jazz & JZ & \(165\pm 10\) & 12.2 \(\pm\) 0.2 & 0.52 \(\pm\) 0.05 \\
22 & Cameo & CM & \(334\pm 26\) & 13.7 \(\pm\) 0.4 & 0.39 \(\pm\) 0.03 \\
23 & Honey Crips & HC & \(342\pm 28\) & 14.0 \(\pm\) 0.3 & 0.53 \(\pm\) 0.05 \\
24 & Mollie’s Delicious & MD & \(280\pm 20\) & 13.5 \(\pm\) 0.2 & 0.29 \(\pm\) 0.04 \\
25 & Modi & MI & \(195\pm 14\) & 13.8 \(\pm\) 0.3 & 0.42 \(\pm\) 0.02 \\
26 & Qinguan & QG & \(332\pm 22\) & 13.9 \(\pm\) 0.1 & 0.16 \(\pm\) 0.01 \\
27 & Qinyang & QYG & \(210\pm 15\) & 12.1 \(\pm\) 0.1 & 0.25 \(\pm\) 0.01 \\
28 & Qinyue & QYE & \(182\pm 13\) & 13.2 \(\pm\) 0.2 & 0.29 \(\pm\) 0.02 \\
29 & Qinyun & QYN & \(190\pm 14\) & 13.3 \(\pm\) 0.3 & 0.26 \(\pm\) 0.01 \\
30 & World No.1 & W1 & \(510\pm 35\) & 14.5 \(\pm\) 0.3 & 0.26 \(\pm\) 0.01 \\
31 & Weijke & WJK & \(305\pm 25\) & 12.8 \(\pm\) 0.2 & 0.51 \(\pm\) 0.04 \\
32 & Alps Otome & AO & \(50\pm 5\) & 14.0 \(\pm\) 0.2 & 0.27 \(\pm\) 0.03 \\
33 & Red Delicious & RD & \(295\pm 15\) & 13.5 \(\pm\) 0.3 & 0.32 \(\pm\) 0.02 \\
34 & Yuhuzaofu & YH & \(305\pm 16\) & 13.4 \(\pm\) 0.2 & 0.41 \(\pm\) 0.03 \\
35 & Pink Lady & PL & \(183\pm 13\) & 14.8 \(\pm\) 0.3 & 0.52 \(\pm\) 0.04 \\
36 & Changfu No.2 & CF2 & \(330\pm 26\) & 15.4 \(\pm\) 0.3 & 0.15 \(\pm\) 0.01 \\
37 & Panama & PNM & \(246\pm 18\) & 12.0 \(\pm\) 0.2 & 0.28 \(\pm\) 0.02 \\
38 & Ruixue & RX & \(296\pm 21\) & 14.5 \(\pm\) 0.2 & 0.30 \(\pm\) 0.02 \\
39 & Ruiyang & RY & \(285\pm 20\) & 13.5 \(\pm\) 0.1 & 0.33 \(\pm\) 0.03 \\
40 & Ruixianghong & RXH & \(165\pm 15\) & 14.9 \(\pm\) 0.2 & 0.24 \(\pm\) 0.02 \\ \hline \end{tabular}  
* \(\;\)  
\end{table} 
Table 1: Apple cultivars used in this study and some basic fruit quality parameters. headspace bottle was equilibrated at 50 \({}^{\circ}\)C for 10 min on a metal heating platform with agitation.