# Impact of Selected Yeast Strains on Quality Parameters of Obtained Sauerkraut
## 1 Introduction  
Yeasts play a minor role in sauerkraut production compared with lactic acid bacteria (LAB), but they still contribute to the fermentation process. While lactic acid bacteria are primarily responsible for converting sugars into lactic acid, which preserves the cabbage and gives sauerkraut its tangy flavour, yeasts can also be present in the fermentation environment. Yeasts can occur naturally on the surface of the cabbage or be introduced from the surrounding environment [1].  
In sauerkraut production, yeasts can contribute to the fermentation process by metabolising sugars and producing alcohol and carbon dioxide. However, their contribution to the overall flavour and texture of sauerkraut is usually less significant than that of lactic acid bacteria. Furthermore, the acidic environment produced by lactic acid bacteria restricts the growth of the majority of yeasts, thereby limiting their activity during the fermentation process [2].  
Although yeast is not as prominent in sauerkraut production as lactic acid bacteria, its presence underlines the complexity of the microbial interactions involved in the fermentation process. In general, the combined activity of yeast and lactic acid bacteria contributes to the unique flavour, texture and preservation of sauerkraut [3].  
The quality of sauerkraut is significantly impacted by the conditions under which fermentation occurs and the microbiota involved in the process. In Poland, it is common practice to add NaCl at a concentration of 2-2.5% and to ferment the cabbage in tanks, often made of concrete. To isolate the cabbage from the external environment duringferentation and release the juice necessary for fermentation, these tanks are often covered with a plastic bag filled with water and pressure is applied [2]. However, this system is not completely airtight and allows oxygen to enter the tank, which alters fermentation conditions and the microbiota present. The proliferation of yeasts, particularly film-forming strains, is encouraged as a result, which alters the chemical composition of the fermented vegetable. These yeasts use organic acids, especially lactic acid, as a carbon source, resulting in a decrease in acidity and an increase in pH. These changes can lead to the growth of spoilage bacteria and other spoilage microorganisms [3].  
Our previous research has shown that cultures of _Debaryomyces hansenii_, _Rhodotorula mucilaginousa_ and _Pichia fermentans_ are consistently detected during sauerkraut fermentation, irrespective of the cabbage variety used and the fermentation conditions (anaerobic/semiaerobic). Representatives of the two species _Clavispora lusitanae_ and _Wickerhamomyces anomalus_ only occur in environments with or without oxygen [4].  
The aim of this research was to determine the influence of yeast strains (previously isolated from different stages of the fermentation process) on selected quality parameters of sauerkraut. The most important parameters for the quality of sauerkraut were analysed, such as the content of the main organic acids, sugars and polyols, the profile of volatile compounds and the CIE LAB colour, and a sensory analysis of the aroma of sauerkraut was carried out using the QDA (quantitative data analysis) method.