This thesis examines the development of yeast postbiotics and probiotics. Currently, the only yeast species commercially utilized for its probiotic properties is Saccharomyces cerevisiae var. boulardii. However, there are other yeast species whose properties and composition could contribute to the development of new, health-promoting microbial products.
As part of the theoretical review, probiotics, postbiotics, and the potentioally probiotic species of yeast were generally characterized. Attention was focused on species of the genera Rhodotorula, Metschnikowia, Yarrowia, and Pichia. Based on the growth characteristics of probiotic microorganisms, an analysis of methods for determining probiotic activity was conducted. The experimental part of the thesis involved testing the probiotic growth characteristics by culturing selected yeasts at body temperature and determining their ability to form biofilms. The postbiotic character of the yeast biomass was characterized by determining the fatty acid profile using gas chromatography, determining the content of carotenoids and other isoprenoids using HPLC, and determining the total saccharide content. Furthermore, the antioxidant capacity and antimicrobial activity of the yeast biomass and supernatants were determined. The cytotoxicity of the yeasts on the Caco-2 cell line was determined, and the cultivation of probiotic bacteria in yeast extracts was performed.
The yeast species Rhodotorula mucilaginosa, Metschnikowia chrysoperlae, and Pichia pastoris exhibited excellent growth properties in terms of biofilm formation and tolerance to body temperature. From a nutritional standpoint, yeast biomass has a good ratio of saturated to unsaturated fatty acids, contains a range of antioxidants and other bioactive compounds, serves as an effective prebiotic for probiotic bacteria, and exhibits low cytotoxicity toward model intestinal epithelial cells. The yeast extracts also demonstrated antimicrobial activity against the tested bacteria.