## 3 Results and Discussion
### Physicochemical and Chemical Characterization of Juices
Similar observations were noted in a previous study on New Zealand Jazz apple juices submitted to different stabilization treatments, in which the amount of 2-hexenal was higher in HPP-processed juices compared with the heated products [9]. Other typical apple flavor compounds are esters with fruity aromatic notes; among those, hexyl n-valerate, hexyl caproate, butyl caproate, and hexyl butyrate were the more abundant in fruits (Supplementary Table S1). All these volatiles have been identified as characteristic of different apple cultivars' flavor [50; 51; 52]. Regarding juices, the statistically lowest ester quantity was found in GD fresh and pasteurized juices in respect to the other cultivars (Supplementary Table S2). Among the stabilization treatments, the TT induced an increase in total ester amounts in all the considered cultivar volatile fractions: in PIN and RD juices, the ester content was statistically more affected by heating in respect to GD products, while HPP treatment maintained, statistically unchanged, the initial ester concentration (Figure 3). The behavior of these components seemed to be related to the cultivar, as observed in previous studies in which the content of hexyl acetate contributed to differentiate apple juices on the basis of the variety [49]. No significant differences were detected among the total alcohol amount calculated for the three cultivars. The main representative compounds were hexanol and 2-hexen-1-ol with herbal and leafy notes, as shown in a previous study [21]. HPP treatment induced a significant decrease in total alcohol content only in RD juices, compared with NT; among the treatments, TT and HPP processes leaded to a diminution of total alcohol amount, in both PIN and RD juices, while in GD cultivar, alcohols were preserved after processing. This trend was mainly determined by hexanol, while 2-hexen-1-ol content was diminished by processing (Supplementary Table S2). While [PERSON] et al. (2004) hypothesized that a decrease in alcohols could be caused by heating [49], other studies showed a rise of these compounds in the volatile fraction of apple juice, after the thermal treating, in comparison with the fresh and the HPP-processed product [12]. Among terpen, \(\alpha\)-farnesene resulted the most representative compound, both in fruit and juices (Supplementary Tables S1 and S2), as reported for several cultivars as \"Mela rossa Val Metauro\" [53], Red Delicious, Mc Inthosh, Gala, and Empire [54]. Results obtained for  
Figure 3: Volatile composition and amount of juices pertaining to three apple cultivars and different processes. juces showed a statistically significant interaction between factors, cultivar, and treatment, for total terpene amounts and for \(\alpha\)-farnesene. Among cultivars, only for GD a statistically higher concentration of terpen was found in HPP-treated product (\(1.23\pm 0.6\) ppm), while only with HPP did the GD samples show a statistically higher content of terpen and \(\alpha\)-farnesene compared with the other two cultivars (\(0.09\pm 0.0\) ppm for PIN and \(0.43\pm 0.2\) ppm for RD) (Figure 3). The trend of \(\alpha\)-farnesene is probably linked to fruit variety, as it was indeed demonstrated in previous studies; the amount of \(\alpha\)-farnesene was fundamental in the classification of apple juice samples pertaining to different cultivars, such as Jonagold and Bramley [28]. Even though no statistically significant differences were found among fruit aromatic fractions, GD showed higher \(\alpha\)-farnesene concentration than the other two cultivars (Supplementary Table S1). For this reason, HPP-treated GD juice presented a more elevated \(\alpha\)-farnesene amount. However, this aromatic compound is lost during stabilization treatments, as verified by [PERSON] et al. (2004) [49]. Finally, sulcato resulted the only ketone maintained in juice aromatic fraction, with a statistically higher concentration in GD juice treated with high pressure (0.13 \(\pm\) 0.0 ppm).