# How Different Fermentation Type Affects Volatile Composition of Plum Jerkums
## 3 Results and Discussion
### Volatile Compounds of Fresh Plum Musts

Table 4: _Cont._The next largest groups of volatile compounds were alcohols and carbonyl compounds. Hexanol (with herbal ethereal alcoholic green aroma) was the most abundant of the nine alcohols detected in fresh musts and constituted of over 90% of alcohols. This is in agreement with the results presented in other studies which indicated hexanol as a characteristic compound in plums [24; 25; 29]. The origin of C6 alcohols, e.g., 1-hexanol, is related to the lipoxygenase activity, which occurs in plants mainly in fruits. It brakes unsaturated fatty acids and the products of such reaction are precursors of short chain alcohols. After fermentation, in analyzed samples some of other alcohols have occurred, e.g., propanol and isobutanol. Those compounds could be produced by yeast from amino acids and they naturally occur in wines [30; 31]. As well as in the case of esters, the concentration of most of these compounds were higher in juices fermented with _H. uwarum_ H2 or _S. cerevisiae_ S1, especially in Wegierka Zwykla and Stanley cultivars in comparison to samples fermented with Ethanol RED (Table 5). Musts fermented with _S. cerevisiae_ S1 demonstrated higher concentrations of propanol, isobutanol, butanol, and 2-phenylethanol. Concentration of the last of these compounds was also high in samples fermented with Ethanol RED (_S. cerevisiae_). It is claimed, that _Saccharomyces_ genus is able to produce significant amounts of 2-phenylethanol and it is currently receiving attention as yeast having a great prospect in development of biotechnological production of this substance [32]. Increased production of higher alcohols by _H. uwarum_ was claimed, but there is no information on the increased synthesis of methanol by this strain. However, according to our studies, concentration of methanol in samples fermented with _H. uwarum_ H2 was the highest and exceeded 950 mg/L. According to results presented by other authors, concentration of methanol in plum wines varies from 175 mg/L to almost 1000 mg/L [33; 34]. Methanol is produced by the hydrolysis of methyl ester groups in pectins from fruits, so it is present in wines and spirits. The enzyme which catalyzes that reaction (pectin methyl esterase) occurs not only in plants, but it may also be produced by various microorganisms [9]. The main reason standing behind high methanol concentrations in our samples was the application of pectinolytic preparation and using whole plum fruits, including skins and stones. \begin{table}
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In the current study, the most abundant aldehydes in fresh musts were 5-methyl-3-hexanone (fruity aroma) and hexanal (grassy scents). Moreover, except for hexanal, we identified other aldehydes and alcohols of six-carbon atoms in all cultivars. 2-hexenal, hexanal, 2-hexenol, 3-hexenol, and hexanol are characteristic for plums and contribute to the green note of the fruit. Those compounds might be formed when the fruit tissues are crushed or blended and the compounds of cytosol and cell walls are exposed to lipoxygen-nases. The presence of these compounds is probably due to lipoxygenase activity, which is initialized by the disruption of the fruit tissues when it is crushed or blended [35]. Other carbonyl compound identified in plum musts was nonanal (woody-like aroma) which could be found in waxes that cover the skin of plum fruit [35]. Some carbonyl compounds were characteristic for particular cultivars (regardless of the type of fermentation carried out), e.g., 2-heptenal in fermented musts obtained from Wegierka Dabrowicka and Wegierka Zwyklad and 2-buten-1-one, from Wegierka Dabrowicka and Cacanska Lepotica.