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Pediococcus pentosaceus and Pediococcus acidilactici are homofermentative Gram-positive cocci that are regularly found in the nonstarter population of raw milk cheeses at the end of ripening. They are known to contribute to the ripening process by their ability to degrade amino acids resulting in important precursors for flavor compounds [1]. In this study, we determined the impact of the above-mentioned species on the amino acid profiles of a cheese with propionic acid fermentation. They were applied as single or mixed cultures Pep1 (P. pentosaceus FAM 19132 [1] & FAM 19144), Pep2 (P. pentosaceus FAM 18321) and Pac1 (P. acidilactici FAM 20063 & FAM 13473 [1]) with two different Propionibacterium freudenreichii cultures in a full factorial experiment. Pep1 had a significant impact on proteolysis in cheese by increasing the amount of free amino acids. Therefore, all amino acids originating from casein were more abundant in cheeses with Pep1 with the exception of arginine whose content was low in all cheeses because of an active arginine deiminase pathway in all three Pediococcus cultures. Although P. pentosaceus exhibits serine dehydratase activity in vitro, no effect on serine degradation was found in cheese. For Pep2, no relevant effects could be observed. Pac1 proved to have an active amino acid degrading ability; in the cheeses with Pac1, serine and threonine had been converted to alanine and -amino butyric acid. P. acidilactici had previously been shown to possess a threonine dehydratase [2], which catalyses the degradation of serine and threonine to pyruvate. Moreover, the contents of glutamic acid, glutamine, glycine, leucine, methionine, valine and ornithine were increased in the presence of Pac1. References [1] S. Irmler, T. Bavan, A. Oberli, A. Roetschi, R. Badertscher, B. Guggenbühl, H. Berthoud, Applied and Environmental Microbiology, 2013, doi.org/10.1128/AEM.03085-12 [2] A. Wenger, R. S. Schmidt, R. Portmann, A. Roetschi, E. Eugster, L. Weisskopf & S.Irmler, AMB Express 2020, doi.org/10.1186/s13568-020-01034-2