Characterization and stress-protective action of Saccharomyces cerevisiae extracellular peptide factors on propionic acid bacteria

Protective effect of Saccharomyces cerevisiae exometabolites (RF1 and RF2) on seven strains of propionic acid bacteria under exposure to bile salts and acid stress was studied. RF2 had a stronger protective effect than RF1. Comparison of the analytical profiles of RF1 and RF2, separated by RP-HPLC, showed that nearly 80% of RF1 components were present in RF2. Separation of S. cerevisiae RF1 into individual components by means of semi-preparative RP-HPLC was used for structural characterization of the active component of the RF1 fraction. It was found to contain two pentapeptides (<1 kDa) with identical amino acid sequences (1Gly-Pro-Tre-Gly-Pro5), differing in one hexose residue. The RF2 separation method based on three-stage liquid chromatography at low and high pressure was developed, which involved analytical high-pressure gel chromatography. The use of the latter method made it possible to separate high-molecular components and perform enrichment of low-molecular peptides. Peptide origin of the RF2 active substances with molecular masses allegedly below 300 Da was confirmed.