## Results and Discussion
### Principal Component Analysis  
A comprehensive view of the phytochemical composition as well as the aroma volatile profile of the two perilla chemotypes in response to mild-salinity as chemical eustressor was obtained through principal component analysis (PCA). The first three principal components (PCs) were associated with eigenvalues higher than 1 and explained 87.1% of the cumulative variance, with PC1 accounting for 47.7%, PC2 for 31.2% and PC3 for 8.2% (Table 5). PC1 was positively correlated with visual appearance traits (L* and b*), the two bivalent cations (Ca\({}^{2+}\) and Mg\({}^{2+}\)), and several volatile compounds (perillene, caryophyllene, perilla ketone, _cis_-jasmone, 4-trifluoroacetylimidazole and thymoquinone); it was negatively and strongly correlated to sinapic acid, total polyphenols, benz-aldehyde, perilla aldehyde and durenol (Table 5). PC2 was positively correlated to fresh yield, dry biomass, protein, nitrate and chlorophyll a contents and negatively associated with rosmarinic acid, 2-hexenal and 1-octen-3-ol. Moreover, the loading matrix indicates the relations among the examined qualitative variables, based on which the two vectors with an angle lower than 90\({}^{\circ}\) are positively correlated, while an angle higher than 90\({}^{\circ}\) means that these variables are negatively correlated. In the current study, variation in Na\({}^{+}\) concentration was most closely aligned with leaf dry matter percentage, and variation in total polyphenols was strongly correlated to perilla aldehyde (Figure 1). \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Principal Components** & **PC1** & **PC2** & **PC3** \\ \hline Eigenvalue & 15.3 & 10.0 & 2.6 \\ Percentage of variance & 47.7 & 31.2 & 8.2 \\ Cumulative variance & 47.7 & 78.9 & 87.1 \\ \hline Eigen vectors a & & & \\ Fresh yield & 0.208 & **0.808** & 0.498 \\ Shoot dry biomass & 0.383 & **0.735** & 0.505 \\ DM b & 0.318 & **\(-\)0.891** & 0.034 \\ L* & **0.941** & \(-\)0.310 & 0.042 \\ a* & **\(-\)0.991** & \(-\)0.019 & \(-\)0.005 \\ b* & **0.993** & 0.012 & 0.024 \\ PO43\({}^{-}\) & 0.310 & **0.843** & \(-\)0.133 \\ K+ & \(-\)0.397 & **0.905** & \(-\)0.092 \\ Ca2+ & **0.937** & \(-\)0.248 & \(-\)0.058 \\ Mg2+ & **0.809** & 0.518 & 0.157 \\ SO42\({}^{-}\) & 0.104 & \(-\)0.137 & 0.559 \\ Na+ & 0.340 & **\(-\)0.849** & \(-\)0.336 \\ Cl* & 0.040 & **\(-\)0.924** & \(-\)0.166 \\ Protein & 0.446 & **0.881** & \(-\)0.111 \\ Nitrate & 0.177 & **0.916** & 0.069 \\ Chlorophyll a & \(-\)0.498 & **0.783** & \(-\)0.148 \\ Rosmaric acid & 0.024 & **\(-\)0.689** & 0.029 \\ Caffe acid & \(-\)0.120 & 0.001 & **0.888** \\ Sinapic acid & **\(-\)0.993** & 0.098 & 0.040 \\ Phenols & **\(-\)0.872** & 0.027 & 0.202 \\
2-Hexenal & \(-\)0.268 & **\(-\)0.701** & **0.629** \\ Benzaldehyde & **\(-\)0.917** & 0.301 & \(-\)0.130 \\ Perilla aldehyde & **\(-\)0.969** & 0.008 & 0.097 \\
1-Otten-3-ol & \(-\)0.272 & **\(-\)0.771** & 0.067 \\ Durenol & **\(-\)0.993** & 0.038 & 0.074 \\ \(\beta\)-Linalool & \(-\)0.586 & \(-\)0.0675 & 0.283 \\ Perillene & **0.914** & 0.139 & 0.159 \\ Caryophyllene & **0.777** & \(-\)0.302 & 0.347 \\ Perilla ketone & **0.892** & 0.071 & \(-\)0.169 \\ _cis_-jasmone & **0.876** & \(-\)0.134 & 0.024 \\
4-trifluoroacetylimidazole & **0.868** & \(-\)0.053 & 0.164 \\ Thymoquinone & **\(-\)0.952** & \(-\)0.055 & 0.127 \\ \hline \hline \end{tabular}  
* Boldface factor loadings are considered highly weighed; b DM, dry matter.  
\end{table} 
Table 5: Eigenvalues, relative and cumulative proportion of total variance, and correlation coefficients for each nutritional trait with respect to the three principal components. The efficacy of PCA for plotting species/cultivars characterization as well as its interpretive usefulness in preharvest and postharvest studies on multiple quality traits has been reported previously in a series of scientific papers [38; 63; 64].