## 4 Discussion  
Overall, the outliers detected from the total areas did not match with those detected by the percentages because of the potential variability in the analysis and intensity of aroma among fruits. Transformation of the percentages into logarithms of the variables of compound classes based on percentages is not advisable except for classification or prediction purposes. The PLS-DA of the total area (with or without normalization of each compound class to the response of the internal standard) gave a higher number of outliers compared with PCA (Supplementary Materials Figure S2 vs. Figure 1), \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**RT** & **Chemical** & \multirow{2}{*}{**Volatile Organic Compound**} & **Linear Retention** & **Match** \\
**Mean** & **Abstract Service** & & **Index Calculated** & **Quality Mean** \\ \hline
**(Min)** & **Name** & **(IUPAC Name)** & **(ud)** & **(\%)** \\ \hline
1.279 & 000074-93-1 & Methanethiol & \textless{}400 & 92 \\
3.572 & 000624-92-0 & Methyldisulfanylmethane & 737 & 94 \\
4.143 & 000071-41-0 & Pentan-1-ol & 763 & 88 \\
4.949 & 00006-25-1 & Hexanal & 799 & 92 \\
7.581 & 000111-27-3 & Hexanal-1-ol & 867 & 90 \\
8.974 & 000111-71-7 & Heptanal & 902 & 91 \\
11.951 & 000100-52-7 & Benzaldehyde & 954 & 83 \\
12.427 & 003658-80-8 & Methylsulfanyldisulfanylmethane & 962 & 88 \\
14.814 & 000124-13-0 & Octanal & 1004 & 89 \\
16.607 & 000104-76-7 & 2-ethylhexan-1-ol & 1033 & 86 \\
18.709 & 000098-86-2 & 1-phenylethanolamine & 1067 & 92 \\
20.146 & 000617-94-7 & 2-phenylpropan-2-ol & 1091 & 81 \\
20.814 & 000124-19-6 & Nonanal & 1107 & 94 \\
20.916 & 004621-04-9 & 4-Isopropylcyclohexanol (isomer) & 1114 & 75 \\
21.433 & 000464-49-3 & 1,7,7-trimethylbicyclo[2.2.1]heptan-2-one & 1151 & 95 \\
21.629 & 010340-23-5 & (\(Z\))-non-3-en-1-ol & 1165 & 81 \\
22.015 & 000098-19-1 & 1-tert-butyl-3,5-dimethylbenzene & 1193 & 72 \\
22.112 & 000112-40-3 & Dodecane & 1200 & 82 \\
22.177 & 000112-31-2 & Decanal & 1208 & 92 \\
22.911 & 71186-24-8 & (6Z)-6-[(\(E\))-but-2-enylidene]-1,5,5- & 1305 & 59 \\  & & trimethylcyclohexene & 1400 & 65 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main volatile organic compounds extracted by headspace solid phase microextraction, measured by gas-chromatography coupled to mass spectrometry and tentatively identified by deconvolution analysis versus NIST11 database. Chemical compound were identified in more than 90% of the melon fruit samples analyzed (outliers excluded from the calculations) in order of retention time. The column used was an HP-5 MS UI. while, in percentages, these differences were minimized. Outliers detected by box-whisker plots were also more frequent than in this case because the variables frequently could not be analyzed by assuming normality, as demonstrated by the Shapiro-Wilk test. This problem also meant that [PERSON]'s test could not be used in our case. The main problem with applying [PERSON]'s test is that individual variables can only be used if they follow a normal distribution, thus losing the perspective of a multivariate analysis. Additionally, this test can only be applied to the two fruits with extreme distribution data [10]. However, more than one fruit could be considered as an outlier in one extreme, particularly if the variable does not follow a normal distribution. An important point when two seasons are being compared is that the potential anomaly detected by the box-whisker plot should be in the same range (Figure 3), which probably explains why more outliers were not found in the multivariate statistical analysis compared with box-whisker plots. The outliers detected by correlation analysis (Figure 4) were more than those finally considered as strong outliers. Removing all of them from certain variables of compound classes using this methodology or box-whisker plot would be problematic for considering the whole aroma of a fruit, and also incorrect from a multivariate point of view.