# Impact of Selected Yeast Strains on Quality Parameters of Obtained Sauerkraut
## 3 Results and Discussion  
### Organic Acids and Sugars  
Yeast is consistently present during sauerkraut fermentation. The conditions prevailing during this process may increase or limit their proliferation. They also influence the qualitative composition of the yeast microbiota [4]. Previous studies have demonstrated that representatives of the species _Debaryomyces hansenii_, _Rhodotorula mucilaginousa_ and _Pichia fermentatus_ are present during sauerkraut fermentation regardless of the prevailing conditions. Aerobic conditions facilitate the growth of the yeast _Wickerhamomyces anomalus_, while anaerobic conditions promote the development of _Clavispora lusitaniae_. In the current research, our aim is to demonstrate how isolated yeast strains influence the quality of sauerkraut produced. To achieve this, we introduced cells of different yeast isolates into salted cabbage in quantities sufficient for them to propagate and colonise the environment. We selected the Galaxy variety for fermentation, which is commonly utilised by sauerkraut producers in Poland. Lactic acid is widely acknowledged as the most crucial component of sauerkraut, as it not only contributes to its characteristic sensory attributes but also enhances its microbiological stability. Fully fermented sauerkraut usually contains 1.8-2.3% acid, which is calculated as lactic acid, resulting in a pH of 3.5 or lower [7]. Throughout the fermentation process, the content of lactic acid, the main product of sauerkraut, gradually increases, ranging from 6.99 to 9.78 g/kg on day 30 [8]. Sauerkraut produced without the addition of yeast contained 9.3 g/kg of lactic acid. The remaining samples can be categorised into two groups: those exhibiting a higher content compared with that of the control and those with a lower lactic acid concentration compared with that of the control (Table 2). The former group includes sauerkraut produced with the yeast _D. hansenii_, while the latter comprises the rest of the samples. There have been no reports so far regarding the ability of the yeast _D. hansenii_ to produce lactic acid. However, as indicated by previous research, certain yeast cultures have been shown to facilitate the growth of lactic acid bacteria [9]. Furthermore, _D. hansenii_ has been suggested to provide essential growth factors for bacteria, including vitamins (such as lactoflavone, thiamine, pantothenic acid, nicotinic acid, folic acid and biotin), amino acids, and aroma components, as well as lipolytic and proteolytic enzymes, all of which contribute to the ripening process of certain fermented foods [10]. Yeast can potentially pose a risk as a food spoilage microorganism by consuming lactic acid, raising the pH and creating favourable conditions for the proliferation of other spoilage microorganisms [11]. The most significant reduction in lactic acid, by 2.8 g/kg compared with that of the control, was observed in sauerkraut obtained with the yeast strains _W. anomalous_ Wa1 and _P. fermentans_ Pf9 (Table 2). Representatives of the former _Pichia_ genus are known for their ability to assimilate various carbon substrates, including organic acids [12]. Their presence, particularly in the form of a film on the surface of the product, often leads to deacidification and sensory alterations in the product [13]. The second important organic acid formed during fermentation is acetic acid [14]. Once again, the highest levels of acetic acid were observed in sauerkraut produced with the yeast _D. hansenii_. In contrast, the lowest amount of this compound, nearly half of that in the control, was generated in samples inoculated with _R. mucilaginous_ Rm26 and _P. fermentans_ Pf9 (Table 2). Yeast species can produce varying amounts of acetic acid, influenced by their specific characteristics and the prevailing fermentation conditions. Some yeast strains have the ability to metabolise acetic acid into biomass, as well as a wide variety of aroma compounds, such as acetates [15].