## 3 Results and Discussion
### Identification of Key Parameters at Different Dehydration Degree  
Principal component analysis (PCA), an unsupervised multivariate statistical analysis method, was applied to examine the sample variance and clustering related to the dehydration degree. The PCA score scatter plots of the free and bound forms of volatiles, expressed as ng/berry, are shown in Figure S3. All samples were observed to be located \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Free**} & \multicolumn{3}{c}{**Bound**} & \multicolumn{3}{c}{**Total**} \\ \cline{2-9}  & **R\({}^{2}\)** & _p-Value_ & **RC \({}^{*}\)** & **R\({}^{2}\)** & _p-Value_ & **RC** & **R\({}^{2}\)** & _p-Value_ & **RC** \\ \hline _trans_-2-Hexenol & 0.954 & 0.004 & \(-\)2.087 & & & & & 0.945 & 0.006 & \(-\)0.519 \\ Pentanol & 0.982 & 0.001 & \(-\)0.017 & & & & & & \\ Octanol & 0.996 & 0.003 & \(-\)0.004 & & & & & & \\ _trans_-2-Heprenal & & & & 0.943 & 0.006 & \(-\)0.009 & & & \\ Propyl octanoate & 0.923 & 0.009 & 0.050 & - ** & - & - & 0.923 & 0.009 & 0.050 \\ Benzyl alcohol & 0.980 & 0.001 & \(-\)0.551 & & & & & & \\ Methyl salicate & & & & 0.934 & 0.007 & \(-\)0.031 & 0.935 & 0.007 & \(-\)0.031 \\
2-Methyl-1-butanol & & & & 0.963 & 0.003 & \(-\)0.834 & 0.923 & 0.009 & \(-\)1.450 \\
3-Methyl-1-butanol & & & & 0.960 & 0.003 & \(-\)1.231 & & & \\
**1-Octen-3-ol** & **0.967** & **0.003** & **\(-\)0.011** & **0.943** & **0.006** & **\(-\)0.075** & **0.947** & **0.005** & **\(-\)0.086** \\
2-Methylbutanal & 0.962 & 0.003 & \(-\)0.055 & - & - & - & 0.962 & 0.003 & \(-\)0.055 \\ \(\alpha\)-Terpinene & 0.963 & 0.003 & \(-\)0.048 & & & & & & \\ \hline \hline \end{tabular}  
* Regression coefficient. **: Not detected in this form.  
\end{table} 
Table 2: Results of the unary linear regression analysis (U-LRA) between juice volume per 100 berries (JV100) and volatile contents (\(\upmu\)g/L). inside the 95% confidence interval after [PERSON]'s T2 investigation for the possibility of outliers. For the free fractions, the first two principal components (PCs) explained 86.5% and 12.8% of the overall variance, respectively. The score plot showed a clear separation of T1 from others. Although T2 could be distinguished from T3, T4, and T5 on PC1, the distance between them was much smaller than that of T1. However, T3, T4, and T5 could not be separated completely, in terms of either PC1 or PC2. For the bound fractions, PC1 and PC2 explained 95.0% and 3.5% of the overall variance, respectively. Similar to the PCA result of the free forms, T4 and T5 could not be separated visibly from each other on the score scatter plot of the bound forms. From the results above, it was difficult to find discriminative information for the metabolites between the five dehydration stages by PCA. In order to obtain better discrimination and to further identify the marker metabolites of the different dehydration degrees, the supervised multivariate statistical analysis method of orthogonal partial least-squares discriminant analysis (OPLS-DA) was employed on both free and bound volatiles at different dehydration stages. OPLS-DA (also known as the orthogonal projection to latent structures discriminant analysis in some studies) has been widely used for classification or discrimination in metabolomics [43; 44]. In this study, OPLS was used to develop discriminative analysis models for the free and bound fractions, respectively. The score scatter plots of these two models, shown in Figure 7a,b, illustrated that the OPLS model developed for the free forms of volatiles was a better fit than that of the bound forms, in terms of the discrimination of samples with respect to different dehydration degrees. The samples at the five dehydration stages were well-separated in the former model constructed from the free fractions, while samples were not discriminated well by the later model developed from the bound volatiles. Therefore, the former model was selected for further application in extracting information on marker metabolites at different dehydration degrees.