## 2 Results
### Multivariate Data Analysis of Allium Species Analysed via SPME-GC/MS  
To better visualize the subtle similarities and differences either between _A. sativum_ and _A. cepa_ red cv. or in response to the different drying methods, multivariate data analyses were employed. Principal component analysis (PCA) is an unsupervised clustering process for identifying patterns in data, via reducing the number of dimensions. It can define a limited number of principal components which describe independent variation in the results [3]. In the present study, PCA was first applied to classify the different forms of onion and garlic with respect to their chemical composition and to determine whether a genotype effect could overcome the drying method adopted herein. A commercial dried powder garlic film-coated tablet was also included for comparison. The PCA score plot was able to readily discriminate between both species regardless of the drying method, with garlic samples clustering separately on the positive score values of PC1, whereas onion specimens were positioned at the negative side of PC1 (Figure 1A). The first two components PC1 and PC2 explained 39.3% and 29.4% of the total variance, respectively. Separation based on the type of processing method could not be observed from PCA, suggesting that species-based separation predominates over drying method impact. The corresponding loading plot of PC1 describes the most discriminatory metabolites in each group leading to such segregation and revealing that garlic samples encompassed higher diallyl disulphide, dially trisulphide, and 3-vinyl-1,2-dithiacyclohex-5-ene levels as compared to onion samples (Figure 1B). Interestingly, garlic commercial tablets \"Tomex\" failed to group with other garlic specimens. Examination of the loading plot revealed its enrichment in diethyl phthalate, which was absent from other garlic samples and accounting for its dispersal (Figure 1B). Considering our interest in investigating the possible influence of the three drying methods for each _Allium_ species, a second PCA trial model was constructed for individual specimens of each species. The garlic model score plot (PC1 = 69.9% and PC2 = 26.6%) showed that freeze dried garlic was clearly separated from shade air-dried and microwave-dried garlic along PC1, suggesting degradation of sulphur compounds to a similar extent in both shade air-dried and microwave-dried specimens (Figure 2A). The corresponding loading plot revealed high diallyl disulphide, dially! trisulphide, and 3-vinyl-1,2-dithiacyclohex-5-ene levels in freeze-dried garlic samples (Figure 2B). In agreement with the first PCA results (Figure 1B), distant clustering of samples belonging to commercial garlic preparation \"Tomex\" was due to its enrichment with diethyl phthalate. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Peak No. **} & \multirow{2}{*}{**ct. (min)**} & \multirow{2}{*}{**RI**} & \multirow{2}{*}{**Volatile**} & \multicolumn{6}{c}{**Relative Abundance (\%)**} \\ \cline{5-10}  & & & & \multicolumn{3}{c}{**A. activation**} & \multicolumn{3}{c}{**\(A\).c corpus Red ev. **} \\ \cline{5-10}  & & & & **Fresh** & **Sun-Dided** & **Microwave-Dided** & **Tomes** & **Fresh** & **Sun-Dided** & **Microwave-Dided** \\ \hline
**M1** & 5.867 & 85C & Daily [subplate] & tc. & 0.05 & 0.53 & tc. & - & - & - \\
**M2** & 7.442 & 924 &  
Phthalic acid esters (PAEs) are employed in polymer materials as a plasticizer commonly found in organic solvents not of high grade and our data suggest that they might have originated during the manufacturing process [7]. In spite of the clear separation observed in PCA for freeze dried garlic samples, a supervised method as orthogonal projection to latent structures-discriminant analysis (OPLS-DA) was further applied to help identify metabolites indicative of each processing method.