## 4 Discussion  
There are serious economic and quality reasons to certify the authenticity of varieties used in different food commodities. Moreover, as food processing progresses, for example, from apple fruits to ciders, it becomes extremely difficult to distinguish between varieties [13]. In this respect, a volatilomic pattern may be a useful tool to discriminate between food commodities and varieties. The main precursors of VOCs in apple fruits are fatty acids that are catabolized through \(\beta\)-oxidation and the lipoxygenase (LOX) pathway, which produce aldehydes, alcohols, and esters. Among these, aldehydes are predominant in immature apples, whereas alcohols and esters prevail in ripe/over-ripe fruits [22]. Regarding the different investigated variables (such as apple variety, ripening stage, and yeast strain), apple variety proved to be the primary attribute influencing the quality and aroma properties of apple ciders [23]. Three sources of VOCs in ciders, namely, apple juices, yeast, and yeast metabolism, were reported [4]. In the current study, the main chemical families of VOCs found in ciders that conferred the fermentation bouquet were esters and alcohols, and aldehydes and ketones to a lesser extent, as previously reported [24]. Regarding the different chemical families of VOCs, esters positively contribute to the aroma profile of ciders, bringing fruits and floral sensory properties [25]. More specifically, ethyl hexanoate (sweet, fruits, pineapple, waxy, fatty, ester, green, and banana odour descriptions) was reported as a VOC that increases in ciders in comparison with apple juices [26]. This VOC was associated with the fermentative process and the involved yeast strains [27], and, together with ethyl decanoate and ethyl octanoate, determines fruity and floral aromas in fermented fruit beverages [9]. However, there are other VOCs, such as 2-hexenal and 1-hexanol, which were described as the main contributors to the green odour of apple fruits and juices [4; 28]. Regarding the fermentation process of apple juices, [PERSON] et al. [25] found 3-methyl-1-pentanol to be a VOC that increases its concentration in cider samples from spontaneous fermentation in comparison with ciders from commercial _Saccharomyces cerevisiae_. This might be justified by yeast species associated with the spontaneous fermentation of both _Saccharomyces_ and non-_Saccharomyces_ yeasts (_Hanseniuspora_ genus and _Metschnikovaia pulcherrina_) that could affect concentrations of VOCs in ciders [29]. Styrene is another VOC reported in apple brandy and cider, with odour threshold values ranging between 3.6 to 80 \(\mu\)g L\({}^{-1}\)[30], and in apple fruits [31]. The formation of this VOC may be because high cinnamic acid content and yeast pitching rate, in combination with open fermentation management, cause quick and increased styrene formation during fermentation, as was previously reported for wheat beer [32]. Thus, styrene may be used as an important indicator to monitor the cider-making process (as well as in beers) and management with food authentication purposes. In contrast, other VOCs were not detected in cider samples, such as toluene, which may be due to the toluene degradation pathway of _S. cerevisiae_ (M00418 KEGG pathway) producing benzyl alcohol and benzaldehyde. Both VOCs were found in the current study in ciders. Recently, toluene was reported in apples for the first time [31] and was also