## 3 Results and Discussion
### GC-IMS Analysis of Volatile Profile of Dried Citrus Peel as Effected by Drying Methods  
This study also adopted HS-GC-IMS to determine the volatiles in dried citrus peel of two cultivars prepared from different drying methods. The flavor compounds were characterized by comparing their drift time and retention index from the HS-GC-IMS spectrum (Figure S2) with results shown in Table 3. In Table 3, 60 typical flavor compounds were identified from the topographic maps of dried citrus peel via GC-IMS library searches, and some individual compounds generated several signals due to the existence of different polymerization. Moreover, the identified compounds listed in the gallery plot were combined to show the characteristic flavor fingerprints of different dried Chachi and Ponkan peels in Figure 5, where one row represents one sample, and one column represents the intensity of the compound in different samples. A brighter signal of each compound indicates stronger signal intensity, while a darker signal indicates weaker signal intensity.  
As shown in Figure 5 and Table 3, 14 alcohols, 16 aldehydes, 4 esters, 11 ketones, 4 monoterpenes, 3 acids, and 8 other compounds were detected in volatiles of different dried citrus peel by GC-IMS analysis. By comparing Tables 1 and 3, it can be found that most detected compounds were different between GC-MS and GC-IMS analyses, suggesting that GC-MS and GC-IMS analyses are complementary in volatile analysis, in agreement with the literature [42].  
Figure 5: Gallery plot of the selected signal peak areas obtained from volatiles of dried Chachi and Ponkan peels prepared from three drying methods.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Compound** & **CAS** & **Formula** & **MW** & **RI** & **RT (s)** & **DT (ms)** & **Comment** \\ \hline \multicolumn{6}{c}{Alcohols} \\ \hline
2-Methylpropanol & 78-83-1 & C\({}_{4}\)H\({}_{10}\)O & 74.1 & 655.3 & 178.498 & 1.1728 & Monomer \\
2-Methylpropanol & 78-83-1 & C\({}_{4}\)H\({}_{10}\)O & 74.1 & 638.2 & 170.541 & 1.3634 & Dimer \\
1-Propanol & 71-23-8 & C\({}_{3}\)H\({}_{3}\)O & 60.1 & 562.9 & 141.808 & 1.1113 & \\ Linalool & 78-70-6 & C\({}_{10}\)H\({}_{8}\)O & 154.3 & 1098.9 & 806.393 & 1.2181 & Monomer \\ Linalool & 78-70-6 & C\({}_{10}\)H\({}_{8}\)O & 154.3 & 1099.4 & 807.109 & 1.6902 & Polymer \\ Linalool & 78-70-6 & C\({}_{10}\)H\({}_{8}\)O & 154.3 & 1108.2 & 821.018 & 2.2416 & Polymer \\
1-Menthol & 2216-51-5 & C\({}_{10}\)H\({}_{20}\)O & 156.3 & 1176.5 & 928.37 & 1.8827 & \\
1,8-Cineole & 470-82-6 & C\({}_{10}\)H\({}_{8}\)O & 154.3 & 1024 & 683.053 & 1.2952 & \\
1-Heptanol & 111-70-6 & C\({}_{7}\)H\({}_{10}\)O & 116.2 & 967.5 & 570.796 & 1.3964 & \\ Dodecanol & 112-53-8 & C\({}_{12}\)H\({}_{20}\)O & 186.3 & 1495.5 & 1430.277 & 1.6136 & \\ p-Cymen-7-ol & C\({}_{10}\)H\({}_{14}\)O & 150.2 & 1314.5 & 1145.531 & 1.3218 & \\ n-Hexanol & 111-27-3 & C\({}_{4}\)H\({}_{10}\)O & 102.2 & 875.6 & 394.101 & 1.3286 & Monomer \\ n-Hexanol & 111-27-3 & C\({}_{6}\)H\({}_{14}\)O & 102.2 & 874.4 & 392.236 & 1.6395 & Dimer \\
1-Octanol & 111-87-5 & C\({}_{8}\)H\({}_{18}\)O & 130.2 & 1077.4 & 772.375 & 1.474 & Monomer \\
1-Octanol & 111-87-5 & C\({}_{8}\)H\({}_{8}\)O & 130.2 & 1075.3 & 769.058 & 1.8822 & Dimer \\
2-Methyl-1-butanol & 137-32-6 & C\({}_{6}\)H\({}_{2}\)O & 88.1 & 712.1 & 215.353 & 1.2361 & \\
3-Methyl-1-butanol & 123-51-3 & C\({}_{6}\)H\({}_{2}\)O & 88.1 & 732.7 & 233.387 & 1.2497 & \\ (Z)-3-Hexenol & 928-96-1 & C\({}_{6}\)H\({}_{12}\)O & 100.2 & 868.3 & 383.42 & 1.2298 & \\
2,3-Butaneediol & 513-85-9 & C\({}_{4}\)H\({}_{10}\)O\({}_{2}\) & 90.1 & 791.1 & 291.806 & 1.3693 & \\ \hline \multicolumn{6}{c}{Aldehydes} \\ \hline Hexanal & 66-25-1 & C\({}_{6}\)H\({}_{12}\)O & 100.2 & 793.9 & 294.682 & 1.2569 & Monomer \\ Hexanal & 66-25-1 & C\({}_{6}\)H\({}_{12}\)O & 100.2 & 794.5 & 295.284 & 1.5665 & Dimer \\
2-Methylbutanal & 96-17-3 & C\({}_{6}\)H\({}_{10}\)O & 86.1 & 671.2 & 186.926 & 1.1585 & Monomer \\
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