# Evaluation of Probiotic _Saccharomyces boulardii_ Yeast as a Distillery Strain
## 1 Introduction  
For centuries, humankind has used yeast to obtain products such as bread, kephir, wine, beer, and other traditionally fermented products. However, it is relatively recently that new remarkable properties of yeast as probioticic organisms have begun to be discovered. The only organism classified as yeast with proven probioticic activity is _Saccharomyces cerevisiae_ var. _boulardii_. The discovery of this yeast species is linked to a trip by the French microbiologist [PERSON] to Indochina (today, Vietnam, Laos, and Cambodia). At the time of his research, there was a cholera epidemic in that region. In 1920, [PERSON] noticed that people who drank tea drink with the addition of lychee and mangosteen fruit peels did not contract cholera. He decided to isolate the yeast found on the surface of these fruits. The isolated organism was named \(S\). _boulardii_ and subsequently patented. Biocodex purchased the rights to the patent in 1947 [1]. Genetic studies to determine exact systematics have shown that \(S\). _boulardii_ shares more than 99% of its genome with \(S\). _cerevisiae_, with the closest affinity being shown to be wine strains [2]. Due to this close genetic relationship, the name _Saccharomyces cerevisiae_ varieties _boulardii_ should be used for the correct terminology for this strain, or it should be noted in the text that the abbreviated name is used. The detailed genetic analysis revealed that there are groups of genes with increased copy numbers in the \(S\). _boulardii_ genome. These genes are responsible for encoding proteins that can be classified into two groups: stress resistance (HSP26, SSA3, SED1, HSP42, HSP78, PBS2) and protein synthesis (RPL31A, RPL41A, RFS24B, RPL2B, RSA3). The increasedcopy number of these genes may allow these yeasts to better adapt to stress conditions such as low pH [2]. The yeast _S. boulardii_ is characterised by higher acetic acid production compared to the distiller strain Ethanol Red belonging to _S. cerevisiae_. This is due to the mutation and variable copy number of the SDH1 and WHI2 genes compared to _S. cerevisiae_. Increased acetic acid production at 37 \({}^{\circ}\)C correlates with antimicrobial activity [3]. The traditional classification of yeasts is based on biochemical criteria and morphological characteristics. In 2014, selected biochemical features of nine _S. boulardii_ strains were compared--Table 1 [4]. Two strains were from ATTC pure culture collection; the other seven were isolated from commercially available probiotic preparations. Faced with the compounds tested as potential carbon or nitrogen sources, none of the strains exhibited the ability to assimilate L-arabinose, L-xylose, xylitol, inositol, D-sorbitol, N-acetylglucosamine, D-lactose, D-melozitose, potassium nitrite, or ethylamine. The term \"probiotic\" was first used in 1965 and means \"for life.\" In this context, a probiotic can be an organism or substance that benefits the host's health. Since then, the need for a strict definition of the term has emerged in the scientific and legal world. In 2001, a definition emerged, created by WHO and FAO specialists, that states that a probiotic is a living microorganism that benefits the host's health when administered in the correct dose [2]. There are several ways in which a probiotic can improve health, including modulation of the immune system, interaction with the brain-gut axis, antagonism towards pathogenic organisms, metabolic regulation, antitoxic properties, cell adhesion, mucin production, regulation of the microbiota, trophic actions, and modification of signalling pathways [5]. The probiotic effects of _S. boulardii_ yeast can be divided into four main categories: trophic effect, immune system regulation, antimicrobial activity, and pathogen cell adhesion [6; 7]. Initially, fermentation was mainly used to preserve food. The process also makes creating new products with specific taste qualities possible.