## 2 Results and Discussion
Alcohol dehydrogenase in the fruit mesocarp accumulates throughout ripening [20], and alcohols are usually left undetectable by the consumers. Relatively low alcohol quantities suggest that the fruit is not overripe [42]. Fruit juice pH effectively converts alcohols and aldehydes into flavoring agents [42]. Esters are the main VOCs produced by horticultural crops. Esters, especially straight chain esters, are generally metabolized from fatty acids [43]. The higher the amount of esters, the more pronounced the aroma and the taste of the fruit [44]. Esters, accounting for 25% of the identified compounds, represented the largest group. The composition of esters differed both qualitatively and quantitatively among the peach samples. It has to be noted that the ester distribution is reported to be different within the part of the fruit [36]. The total ester content varied between 25.51% and 34.61% of TIC. Esters contribute to the fruity aroma of peaches [45]. Ethly hexanoate (in the range from 1.38% to 5.76% of TIC) and ethyl tiglate (between 2.78% and 5.4% of TIC) were present at the highest relative concentrations among the estimated esters. Although the amount of esters was predominant in all eight varieties, the relative TIC was two times smaller than the reported literature average [46]. This is most likely due to the specificity of orchard location, light availability, temperature, and season specificity, as well as ecological location. The presence of butanoates (B) and hexanoatees (H) confirms the ripeness of the studied varieties from the averages of 9.48 (B) and 3.89 (H), 10.5 (B) and 2.61 (H), and 7.19 (B) and 5.33 (H) of the TIC in peaches, flat peaches, and nectarines, respectively. Seven hydrocarbons were identified, of which tetradecane and tridecane were dominant. The total content of hydrocarbons was in the range from 7.23 to 10.20% of the TIC among the peach varieties. [PERSON] et al. [47] reported the presence of several hydrocarbons in peaches. Tetradecane is considered a creamy descriptor, whereas dodecane is a woody descriptor [48]. The authors reported the presence of (E)-2-nonen-1-ol, 2-methylpropyl acetate, ethyl butanoate, butyl acetate, 3-methyl-1-butyl acetate, ethyl pentanoate, ethyl hexanoate, hexyl acetate, methyl octanoate, and hexyl hexanoate [47]. Other researchers differentiate ethyl acetate as the major ester compound in both peaches and nectarines [49]. Limonene, linalool, and p-cymene are listed as key flavor compounds that form the characteristic aroma profile [27; 50]. The predominant compound in the nectarine varieties was \(\beta\)-mycrene, while linalool was the most abundant in the peach varieties, bringing out the floral aroma in them. Terpenes contribute to a floral flavor of fruits [51], and a sweetening taste [20], and are the principal components in plant essential oils. Among the eight identified terpen, limonene (0.60-3.26% TIC) and linalool (1.1-2.75% TIC) were in the highest relative concentrations. Linalool was also the major terpenoid compound in other peaches and nectarines [13]. Linalool is reported to possess a floral and citrus-like aroma [52]. Mycrene is a precursor of linalool and is reported as an usual representative in peaches and nectarines, characterizing their aroma with a woody note. The currently established results also prove that the more the linalool, the less the mycrene. Other authors also advocate the thesis that mycrene is found in higher amounts in nectarines [35], which is further supported by the current values. Terpene compounds (i.e., linalool) and alcohols (i.e., 1-hexanol) are reported to be less abundant than aldehydes in apricots and were detected to decrease with ripening [53]. The relative presence of terpen in the eight studied varieties was lower compared to the aldehydes, in accordance with the results mentioned above. The distribution of the main chemical families is presented in Figure 1. The volatile compounds were relatively uniformly distributed.