## 4 Conclusions  
Over the decades, we have looked at food spoilage yeasts as unnecessary and unwanted without considering whether they may possess any positive properties. This often led to oversights and the loss of many potentially interesting strains. The screening procedure used in this study identified eleven isolates, selected on the basis of their gastrointestinal viability at levels similar to or higher than the reference strain _S. cerevisiae_ var. _boulardii_. The strains included the following: one strain of _Candida metapsilosis_ from fermented red kale, six strains of _Metschnikova pulcherrima_ from fermented fruit juice, and four strains of _Pichia kudriavzevii_ isolated from fermented strawberry jam, pumpkin jam, and sourdough. Some of these isolates showed survival rates approximately 1.5-2 times higher than the reference strain. The elimination factor for 107_Metsch_pulcherrima and 111_Metsch_pulcherrima appeared to be the ability to produce biogenic amines, while for 110_Metsch_pulcherrima it was the enzymatic activity of trypsin and beta-glucuronidase. Many of the strains tested were similar to the reference strain or even better in terms of their autoaggregation capacity, hydrophobicity, or antioxidant properties. All isolates showed no haemolytic or antimicrobial activity against important foodborne pathogenic bacteria. We selected the two most promising strains from the screening procedure, 113_Metsch_pulcherrima and 101_Pich_kudriavzevii. However, these yeasts require further genetic and safety studies, including in vivo testing, to confirm their probiotic potential and to conclusively prove that they are safe for humans, although they have been used in biotechnological processes for years. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c} \hline \hline
095 & + & + & \(-\) & + & + & \(-\) & \(-\) & + & \(-\) & \(-\) & \(-\) & + & + & \(-\) & + \\ \hline
096 & + & + & \(-\) & + & + & \(-\) & + & + & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & \(+\) \\ \hline
099 & + & + & \(-\) & + & + & \(-\) & + & + & \(-\) & \(-\) & \(-\) & \(+\) & \(-\) & \(-\) & \(+\) \\ \hline
101 & + & + & \(-\) & + & + & \(-\) & \(-\) & + & \(-\) & \(-\) & \(+\) & \(-\) & \(-\) & \(+\) \\ \hline
105 & + & + & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & + & \(-\) & \(-\) & \(+\) & \(+\) & \(-\) & \(+\) \\ \hline
106 & + & + & \(-\) & + & + & \(-\) & \(-\) & + & \(-\) & + & \(-\) & \(+\) & \(+\) & \(+\) & \(-\) \\ \hline
107 & + & + & \(-\) & + & + & \(-\) & + & + & \(-\) & \(-\) & \(-\) & \(+\) & \(+\) & \(-\) & \(+\) \\ \hline
108 & + & + & \(-\) & + & + & \(-\) & \(-\) & \(-\) & \(-\) & \(+\) & \(-\) & \(+\) & \(+\) & \(+\) & \(-\) \\ \hline
109 & + & + & \(-\) & + & + & \(-\) & + & \(-\) & \(-\) & \(-\) & \(-\) & \(+\) & \(+\) & \(+\) & \(-\) & \(+\) \\ \hline
110 & + & + & \(-\) & + & + & + & + & + & + & + & + & + & + & + & + \\ \hline
111 & + & + & \(-\) & + & + & + & + & + & + & + & + & + & + & + & + \\ \hline
112 & + & + & \(-\) & + & + & \(-\) & + & \(-\) & \(-\) & \(-\) & \(-\) & \(+\) & \(+\) & \(-\) & \(+\) \\ \hline
113 & + & + & \(-\) & + & + & \(-\) & + & \(-\) & \(-\) & \(-\) & \(-\) & \(+\) & \(+\) & \(-\) & \(+\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._As far as we know, this is the first study to focus on the probiotic potential of yeast isolates obtained from spoiled food and beverages by unwanted fermentation. Our research shows that some of the spoilage-derived yeast strains could have probiotic properties, and spoiled food could be used as a source of potentially probiotic strains. We hope that our work will encourage other researchers to look into this direction. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app142411698/s1](https://www.mdpi.com/article/10.3390/app142411698/s1)]([https://www.mdpi.com/article/10.3390/app142411698/s1](https://www.mdpi.com/article/10.3390/app142411698/s1)), Spreadsheet S1: Figure S1. Survivability_Tukey results, Figure S2. Autoaggregation_Tukey results, Figure S3.