# How Different Fermentation Type Affects Volatile Composition of Plum Jerkums
## 3 Results and Discussion
### Volatile Compounds of Fresh Plum Musts
Some of the carbonyl compounds were also identified in jerkums and their concentration was usually higher in samples fermented spontaneously than in other types of fermentation. These compounds included, e.g., hexanal, benzaldehyde, and 2-heptenal. The acetaldehyde is one of the most important carbonyl compounds produced during fermentation, which at low levels contributes to fruity flavors, while high concentrations (200 mg/L) cause flatness in wines [36]. It was present in all analyzed jerkums. Its concentration did not exceed this value and was not dependent on the type of fermentation used. Among terpenoids, linalool, p-cymene, geraniol, and geranyl acetone were dominant compounds in analyzed plum musts. Those compounds (with the exception of geraniol) were also detected in plums _Prunus domestica_ L. cv. [PERSON] as described by [PERSON] et al. [25]. The terpenoids, namely the monoterpenols, were reported as volatile components of fruits responsible for a wide spectrum of aromas, mostly perceived as very pleasant. The compounds are responsible for the varietal aroma of fruits, and at least some of them are present in their glycosidic compounds. The concentration of linalool, which is also present in fresh plum, may increase during technological processing, mostly, by its release from glycosidic forms. That process may occur due to the heat release [37; 38]. Bornylene is an interesting compound which was not detected in plum fruit, so far, however its occurrence was confirmed in kiwi fruit and wines obtained from that fruit [39]. However, this compound was present in Wegierka Zwykla and Cacanska Lepotica cultivars in the current study. After fermentation, the profile of terpenoids was changed and the highest concentration of those compounds was determined in samples fermented spontaneously or with _H. uwarum_ H2. Despite the fact that analyzed samples were immediately frozen after fermentation and stored at \(-18\)\({}^{\circ}\)C, some volatile compounds could be oxidized or transformed into each other. Probably, linalool oxidized to cis-linal oxide (which was present after fermentation) and the aroma of the latter volatile is less intense. In addition to the oxidation processes, other enzymatic and non-enzymatic reactions occur during storage. Terpenoids are reduced by 50-60% after 3 months of storage of wines [40]. It was also noted that during that period those compounds undergo various transformations which result in the formation of cyclic compounds, ketones, lactones (\(\alpha\)-(alpha), \(\beta\)-ionone (beta), and vitispirane [40]. Transformation of terpenoids requires appropriate conditions, e.g., in acidic solutions, geraniol is converted to the cyclic terpene \(\alpha\)-terpineol [41], which also occurred in jerkums (Table 5). The last group of volatile compounds in the analyzed plums was lactones. Among them, \(\gamma\)-nonanolactone and \(\gamma\)-decanolactone were detected. Lactones are formed from the corresponding hydroxy acids. These compounds, particularly \(\gamma\)-lactones, are important compounds in terms of their contribution to the aroma and, in general, pleasant fruity aroma descriptors [37]. Some studies confirmed \(\gamma\)-dodecalactone as the major lactone in plums, especially in Japanese plum (_P. salicina_) and candied plum (_P. domestica_) [25; 37]. Completely different lactones were found in the fermented samples--\(\gamma\)-butyrolactone and \(\varsigma\)-dodecalactone. The \(\gamma\)-butyrolactone, the most common and important lactone in -fermented foods, has a creamy, oily, fatty, or caramel aroma and a milky, creamy taste, with fruity peach-like after-scents [42].