## 2 Results and Discussion
Some aldehyde compounds are formed in the event of frost damage: octanal, heptanal, and pentanal [26]. The different amounts in the studied samples prove that chilling injuries are variety-dependent, and do not follow the ripening period of the peach. Aldehydes are flavor-contributing for premature fruit. They bring out a specific fresh-green odor to the fruit. C\({}_{6}\) aldehyde compounds are desired, especially in not fully ripe pears, plums, and apples. Such compounds decrease in quantity during the process of full ripening of the fruit [27]. Following the abovementioned, it can be concluded that in the absence of other unfavorable conditions, the \"Laskava\" variety, which contains the most aldehydes, can be stored for the longest period, while \"Ufo-4\" and \"Evmolipya\" should reach the market within the shortest time. The median-like flavor of the \"Laskava\", \"Ufo-4\", and \"July Lady\" varieties could be related to (E)-2-nonenal detection [28]. Hexanal is reported in literature [29] as a major compound in the volatile analysis of nectarines, which is further supported in the currently established results for the \"Gergana\" and \"Morsiani 90\" varieties. It is associated with a sweet, fruity taste [30]. Heptanal, 2-hexenal, and octanal, typical for peach varieties, were found to contribute to the fresh odor [31]. Lactones possess high aromatic values in peaches due to their low odor threshold. Lactones, as intramolecular esters of 4- and 5-hydroxy acids, shape the basic peach aroma [22], and have high aroma effects in stone fruits, in general. Among the seven identified ketones, \(\gamma\)-octalactone and \(\gamma\)-dodeclactone, that give peach-like aroma, were in the highest relative concentrations. These lactones act in association with aldehydes, alcohols and terpenoids, which are responsible for the spicy, floral and fruity features in the peach [32]. \(\gamma\)-Decalactone and \(\gamma\)-octalactone are characteristic volatile compounds for peaches. The compound \(\gamma\)-octalactone, which confers a sweet herbaceous, coconut-like odor and taste, was predominant in the \"July Lady\" and \"Laskava\" varieties [33]. \(\gamma\)-Decalactone was most abundant in the two nectarine varieties object of analysis, which supports the literature stating that this is the most common compound identified in the pulp of nectarines [13]. It has to be noted that lactone identification is highly dependent on the extraction conditions, which can be identified as a limitation in every study on the subject. The absence or presence of certain lactones can be due to the assessment methodology being used [34; 35]. For example, other authors have managed to identify more than ten C\({}_{5}\)-C\({}_{10}\)\(\gamma\)-lactones [8; 36]. It has been suggested that lactones in peaches are a result of the \(\beta\)-oxidation pathway of fatty acids [21]. The biosynthesis of fatty acids has been reported to being highly influential on the volatile profile. Eight fatty acids were identified, with hexanoic acid (1.22-6.84% of TIC) being the principle one (Table 1). Nonanoic and dodecanoic acid were the second most abundant of the investigated peach fruits. Fatty acids are important as they serve as carriers for some lipophilic vitamins and bioactive compounds present in fruits, and the presence of essential fatty acids is believed to play an important role in the prevention of cardiovascular diseases [37; 38]. Acids most likely contribute little to the aroma profile though, because they normally have high odor detection thresholds [39]. Alcohols represent approximately 8% of the total identified compounds, with pentanol and nonanol predominating. Pentanol, which is responsible for the bouquet and astringer aroma description [40], was the main alcohol in all the studied samples (in the range from 0.95% to 1.88% of TIC). Benzyl alcohol, found in the highest concentrations in \"Ufo-4\", is described as having a floral aroma [41].