## 2 Results and Discussion
### Profiling of Onion and Lemon Volatiles Using SPME/GC-MS and Multivariate Data Analysis
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Peak** & **rt (min)** & **KI** & **ID** & **Average \(\pm\) Std.** \\  & & & **dev. Fresh** & **dev. Pickled** \\ \hline
1 & 7.03 & 903 & \(\alpha\)-Thujene & 0.15 \(\pm\) 0.11 & 0.04 \(\pm\) 0.03 \\
2 & 7.18 & 912 & \(\alpha\)-Pinene a  & 0.37 \(\pm\) 0.48 & 0.35 \(\pm\) 0.27 \\
3 & 7.48 & 929 & Fenchene & 0.04 \(\pm\) 0.04 & 0.02 \(\pm\) 0.02 \\
4 & 8.03 & 961 & \(\beta\)-Pinene a  & 33.24 \(\pm\) 5.89 & 23.44 \(\pm\) 1.26 \\
5 & 8.16 & 967 & \(\beta\)-Myrcene a  & 0.15 \(\pm\) 0.20 & 0.36 \(\pm\) 0.28 \\
6 & 8.64 & 995 & 1,4-Cineole a  & 0.02 \(\pm\) 0.02 & 0.07 \(\pm\) 0.06 \\
7 & 8.66 & 996 & 2-Carene & 2.12 \(\pm\) 2.69 & 0.17 \(\pm\) 0.13 \\
8 & 8.80 & 1005 & Melilotal & 0.05 \(\pm\) 0.07 & 0.39 \(\pm\) 0.31 \\
9 & 8.94 & 1014 & Limonene a  & 32.10 \(\pm\) 10.45 & 43.49 \(\pm\) 5.16 \\
10 & 9.38 & 1042 & \(\gamma\)-Terpinene & 12.39 \(\pm\) 8.90 & 20.97 \(\pm\) 3.21 \\
11 & 9.76 & 1066 & Terpinolene & 0.10 \(\pm\) 0.13 & 0.52 \(\pm\) 0.41 \\
12 & 9.86 & 1073 & p-Cymenene & 0.02 \(\pm\) 0.03 & 0.19 \(\pm\) 0.15 \\
13 & 10.43 & 1110 & \(\alpha\)-Linalool a  & 0.01 \(\pm\) 0.02 & 0.37 \(\pm\) 0.29 \\
14 & 11.06 & 1154 & Bicyclol[3.2.1]oct-3-en-2-one, 4-methyl- & 0.01 \(\pm\) 0.02 & 0.36 \(\pm\) 0.29 \\
15 & 11.10 & 1158 & \(\alpha\)-Phellandren-8-ol & 0.02 \(\pm\) 0.03 & 0.03 \(\pm\) 0.02 \\
16 & 11.22 & 1166 & 1-Terpinen-4-ol & 0.99 \(\pm\) 0.81 & 0.89 \(\pm\) 0.71 \\
17 & 11.33 & 1173 & p-Cymen-8-ol & 0.02 \(\pm\) 0.03 & 0.05 \(\pm\) 0.04 \\
18 & 11.43 & 1180 & \(\alpha\)-Terpineol & 0.39 \(\pm\) 0.49 & 3.33 \(\pm\) 2.66 \\
19 & 11.56 & 1189 & Unknown & 0.15 \(\pm\) 0.18 & 2.50 \(\pm\) 2.00 \\
20 & 11.97 & 1220 & \(\beta\)-Citral & 3.46 \(\pm\) 4.47 & 0.00 \(\pm\) 0.00 \\
21 & 12.36 & 1249 & \(\alpha\)-Citral a  & 10.86 \(\pm\) 11.79 & 0.00 \(\pm\) 0.00 \\
22 & 13.16 & 1311 & \(\delta\)-Elemene & 0.02 \(\pm\) 0.03 & 0.08 \(\pm\) 0.07 \\
23 & 13.37 & 1328 & 6-Dimethyl-2,6-octaglien-8-yl acetate & 0.70 \(\pm\) 0.90 & 0.24 \(\pm\) 0.19 \\
24 & 14.28 & 1402 & (Z)-\(\beta\)-Farnesene & 0.33 \(\pm\) 0.46 & 0.23 \(\pm\) 0.18 \\
25 & 14.34 & 1407 & (\(E\))-\(\alpha\)-Bergamotene & 2.29 \(\pm\) 2.56 & 0.25 \(\pm\) 0.20 \\
26 & 14.70 & 1437 & Unknown sesquiterpene & 0.00 \(\pm\) 0.00 & 0.01 \(\pm\) 0.01 \\
27 & 15.04 & 1464 & Unknown sesquiterpene & 0.00 \(\pm\) 0.00 & 0.05 \(\pm\) 0.04 \\
28 & 15.08 & 1468 & (Z,\(E\))-\(\alpha\)-Farnesene & 0.02 \(\pm\) 0.03 & 0.80 \(\pm\) 0.63 \\
29 & 15.12 & 1478 & \(\beta\)-Bisabolene & 0.01 \(\pm\) 0.01 & 0.69 \(\pm\) 0.54 \\
30 & 15.80 & 1523 & epi-\(\alpha\)-Eudesmol & - & 0.01 \(\pm\) 0.01 \\
31 & 16.06 & 1541 & Unknown sesquiterpene & - & 0.08 \(\pm\) 0.07 \\  & & Total monoterpene hydrocarbons \% & 80.66 & 89.55 \\  & & Total oxygenated monoterpenes \% & 15.83 & 5.49 \\  & & Total sesquiterpene hydrocarbons \% & 3.37 & 2.44 \\  & & Total oxygenated sesquiterpenes \% & 0.7 & 0.25 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Relative percentiles of volatile components to total peak areas detected in fresh and pickled lemon fruit using SPME/GC-MS measurements (\(n=3\)). Multivariate data analysis was further applied to the volatiles abundance GC-MS dataset to visually demonstrate similarities and differences among specimens. Principal component analysis (PCA) was used as an unsupervised clustering model to highlight the variation based on volatiles abundance peak data. The PCA score plot (Figure S1) modeling fresh and pickled lemon showed no tight clustering of replicates, especially for pickled lemon. Consequently, supervised multivariate data analysis, i.e., OPLS, was employed for samples classification. OPLS-DA outscores PCA in the separation of the predictive variation from orthogonal variation and enhances data interpretation [37]. The OPLS-DA score plot (Figure 2A) showed better discrimination between the sample groups with the pickled group clustering separately from the fresh group. The S-loading plot derived from the OPLS-DA model is represented in Figure 2C.