## 3 Results
### Contribution of Apple Matrices (Fruit, Juice, and Cider) on Volatile Profile  
As stated above, this study allowed for identifying common VOCs among 3 matrices studied from 3 different varieties (Figure 2), and other specifics for each commodity (Table 1). In order to differentiate apple-fruit, -juice, and -cider samples by volatilomic profile, principal-component analysis (PCA) was performed (Figure 3). Figure 3: Principal-component analysis (PCA) of volatile profile of apple fruits, juices, and ciders based on apple variety (\(n=3\) for each data point). Peak number attribution shown in Table 1.  
Figure 2: Relative concentration of volatile organic compounds (VOCs) common to all apple fruits (\(\mathrm{ug}\) kg\({}^{-1}\)), juices, and ciders (\(\mathrm{ug}\) L\({}^{-1}\)) (\(n=3\) for each data point). Thus, effective separation according to apple matrices was achieved. The closeness of the samples on the PCA score plot indicated a similar volatile profile, and the PCA biplot showed the relationship between loadings (VOCs) and variables (fruits, juices, and ciders). The variance of PC1 and PC2 was 41.6% and 19.1%, respectively, representing 60.7% of the total variability of data, allowing for good differentiation among apple fruits, juices, and ciders. Combining the variable-importance-in-projection (VIP) values from PLS-DA higher than 1.6 (data not shown), 15 VOCs were selected as putative markers for discrimination among apple fruits, juices, and ciders. These putative markers were 2-propanol (5), toluene (18), hexanal (22), propyl butanoate (25), 2-hexenal (41), styrene (47), 2-hexen-1-ol isomer (73), ethyl octanoate (79), ethyl nonanoate (96), ethyl decanoate (110), diethyl butanedioate (117), ethyl 9-decenoate (119), 3-(methylthio)-1-propanol (120), 2-phenylethylly acetate (125) and octanoic acid (139). In addition, heat-map clustering based on significant features from ANOVA and [PERSON]'s post hoc test was carried out to display data distribution and to compare the respective relatively quantified levels of VOCs throughout the apple matrices (Figure 4). More specifically, in apple fruits, esters such as butyl butanoate (42), hexyl propanoate (66), butyl hexanoate (75) were related to sweet fruity green apples and over-ripe fruit as odour attributes. One ketone (1-octen-3-one (55)), 1 terpenoid as \(\alpha\)-farnesene isomer ((Z-E)-\(\alpha\)-farnesene) (121), and 1 lactone (2-hydroxy-\(\gamma\)-butyrolactone (141)) were only detected in fruit samples in at least 2 varieties, not identifying either in juices or in ciders. Figure 4: Hierarchical-cluster analysis (HCA). Heat-maps of putative markers identified in apple fruits, juices, and ciders generated by Euclidean distance through Ward agglomerative method (peak number attribution shown in Table 1). Regarding juices, several VOCs were exclusively identified in this matrix, namely, butanal (4), 2,4,5-trimethyl-1,3-dioxolane (7), 1-penten-3-ol (28), 2-penten-1-ol (58), and 2-butoxyethanol (70) with pungent, horseradish, green vegetables, and a tropical-fruit odour description; these VOCs were not identified in either fruit or cider samples. The main chemical families of VOCs found in ciders that formed the fermentation bouquet were esters and alcohols, and aldehydes and ketones to a lesser extent (Figure 1). In this way, among esters, methyl octanoate (71), ethyl nonanoate (96), ethyl decanoate (110), diethyl butanedioate (117), ethyl 9-decenoate (119), and 2-phenylethyl acetate (125) were identified in all cider samples from the 3 investigated varieties (Table 1). Acids could also be important odour compounds in the ciders, such as octanoic acid (139), with a sweaty cheese aroma that was only found in ciders, but not in fruits or juices. However, this VOC was semiquantified below its odour threshold (OT \(\sim\)3000 \(\mu\)g L\({}^{-1}\)). Among alcohols detected in ciders, 2 (3-methyl-1-pentanol (62) and 3-(methylthio)-1-propanol (120)) were identified in the ciders from the 3 varieties.