## 3 Results and Discussion
### Effect of Refrigerated Storage  
A PLS regression was used to evaluate the change in Jazz apple juice volatile fractions during refrigerated storage. For each processing condition, two latent variables adequately explained a considerable amount of the Y-variance (94%, 93% and 97% for thermal, HPP and PEF, respectively) (Figure 2a-c). Accordingly, for each processing conditions, a multivariate PLS regression model using two LVs was selected. The first obvious trend on all three bi-plots is that the apple juice volatile fraction clearly changes during refrigerated storage. This can be seen from the horizontal projection of apple juice volatile fractions from the left to the right side of the bi-plots. This dominant change \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Processing** & **VID** & **Identity** & **RI** \\ \hline \multirow{8}{*}{Control/Unprocessed} & \(-\)0.932 & 2-methylbutan-1-ol & 732 \\  & \(-\)0.886 & 2-methylpropyl acetate & 965 \\  & \(-\)0.882 & hexan-1-ol & 869 \\  & \(-\)0.809 & 3-methyl-2-buten-1-yl acetate & 919 \\  & 0.820 & (_E_)-2-hexenal & 851 \\  & 0.880 & \(\alpha\)-terpineol & 1199 \\  & 0.950 & hexyl acetate & 1010 \\ \hline \multirow{2}{*}{Thermal (72 \({}^{\circ}\)C for 15 s)} & \(-\)0.812 & (_E_)-2-hexenal & 851 \\  & \(-\)0.801 & \(\alpha\)-terpineol & 1199 \\ \hline \multirow{2}{*}{HPP (600 MPa for 3 min)} & 0.836 & 2-methylbutyl acetate & 877 \\ \hline \multirow{2}{*}{PEF (15.5 kV/cm)} & 0.824 & hexan-1-ol & 869 \\  & 0.831 & butyl propanoate & 906 \\  & 0.849 & terpinen-4-ol & 1185 \\ \hline \hline \end{tabular} These volatiles are selected discriminating the process impact immediately after pasteurization. The volatiles are listed in a decreasing order of VID coefficient, where a positive VID coefficient illustrates a higher concentration of a compound after one processing compared to other one and vice versa. The retention index (RI) of compounds is listed. HPP: High-Pressure Processing; PEF: Pulsed Electric Fields; VID: variable identification.  
\end{table} 
Table 1: Discriminant volatile markers in Jazz apple juice for control, thermal, HPP and PEF processing, which are selected by the VID procedure. during storage is adequately described by the first LV, as indicated in the respective axis (at least 80% Y-variance explained). Even though it is minimal, there is also a variation in the vertical direction in addition to the horizontal direction. This second variation on the plot is described by the second LV. On all three bi-plots, most of the volatiles are projected to the beginning of the shelf life, indicating that the amount of these compounds has decreased as a function of storage time. VID coefficients were calculated to determine volatiles significantly changed during storage. As can be seen from Table 2, three, five and four discriminant markers were selected in the thermal, HPP and PEF pasteurized juices, respectively. Figure 2: _Cont._  
The aroma of apple juice is mainly related to volatile compounds such as esters, alcohols, aldehydes, ketones and ethers [17]. Even though the literature search revealed more than 300 volatile compounds in apple juice, only 20-40 odor-active volatiles including ethyl-2-methyl butanoate, ethyl acetate, ethyl butanoate, (_E_)-2-hexenal and 1-butanol are considered as being responsible for apple juice aroma [16; 17; 25; 26]. In the present work, the amount of some of these ester and aldehyde volatile compounds has significantly decreased during storage in all processed samples (see Table 2). This shows that the fresh, green and fruity note of apple juice seem to drop as a function of shelf life. Moreover, esters and aldehydes seem to be the main chemical groups significantly changing during shelf life in all thermal, HPP- and PEF-pasteurized apple juices (Table 2).