# Impact of Selected Yeast Strains on Quality Parameters of Obtained Sauerkraut
## 3 Results and Discussion
### Volatile Compounds
lusitanie_ Cl6, which generally contained the highest amounts of volatile compounds, including alcohols (Table 3). This strain was characterised by the production of the highest amounts of volatile compounds on model media among representatives of this species. It was also characterised by weak killer activity and developed to contain a lactic acid content of 8 g/L [5]. 2,3-Butanediol (2,3-BD) is a bacterial metabolite produced via several intermediates, including \(\alpha\)-acetolate, acetoin (AC) and diacetyl, from pyruvate. The ability to produce 2,3-BD is widespread in bacteria. The Voges-Proskaurer reaction, which is related to the intermediates of 2,3-BD production, is a fundamental test for bacterial classification [29]. Analyses of sauerkraut showed that the highest concentrations of 2,3-butanediol were found in the control sample. The addition of _P. fermentans_ Pf9 yeast reduced the amount of the compound in question by almost 16 times. Yeast can grow on 2,3-butanediol as the sole carbon and energy source, indicating that they have the ability to degrade these metabolites. The resulting product is acetoin, which can be further degraded into simpler substances [30]. The most abundant group of carbonyl compounds in sauerkraut was of aldehydes. Most aldehydes originate from the raw material. They can be formed microbiologically during fermentation as a result of oxidation from alcohols, and the reverse process can occur simultaneously [31]. These compounds play an important role in the flavour formation of food products due to their very low aroma thresholds [32]. Of the five carbonyl compounds detected, nonanal, decanal and dodecanal had the greatest impact on the aroma of sauerkraut. Their levels were, in most cases, higher in sauerkraut to which yeasts had been added, especially _D. hansenii_ and _Cl. lusitanie_. The second largest group of volatile compounds after alcohols was of esters (Table 4). These are mostly formed via the enzymatic condensation of alcohols and organic acids [31]. The largest amounts contained ethyl acetate, dibutyl succinate and ethyl 2-methylocanoate. The lowest number of esters was found in the control sample and in sauerkraut obtained with _P. fermentans_ Pf9 and _W. anomalus_ Wa7. The highest number was found in samples with _D. hansenii_ and _Cl. lusitanie_, which differed significantly in their ester profiles. For example, sauerkraut fermented with _Cl. lusitanie_ contained the most ethyl acetate, dibutyl succinate, benzyl benzoate and ethyl hexadecanoate, _D. hansenii_ Dh17--phenethyl acetate, ethyl decanoate and 1-methylethyl dodecanoate, while _W. anomalus_ strains contained the most 2-butoxyethyl acetate and ethyl dodecanoate. Therefore, an excessive amount of esters may indicate a yeast infection during fermentation. Lactones are a group of volatile organic compounds (VOCs) that are classified as esters of hydroxy acids and are defined by a cyclic ring. They are produced through lipid metabolism and have low perception thresholds [33]. Previous research has indicated lactic acid bacteria as the main producers of gamma-lactones during the fermentation of sauerkraut [34]. The results of our research indicate that yeast can also influence the formation of larger amounts of compounds from this group. The highest amounts of gamma-lactones were found in sauerkraut obtained with the addition of _Cl. lusitanie_. This could be due to the direct synthesis of these compounds by yeast or the provision of appropriate precursors to lactic acid bacteria.