The narrowing down of inoculated communities of coagulase-negative staphylococci in fermented meat models is modulated by temperature and pH

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Coagulase-negative staphylococci (CNS) are involved in colour and flavour formation of fermented meats. Their communities are established either spontaneously, as in some artisan-type products, or using a starter culture. The latter usually consists of Staphylococcus carnosus and/or Staphylococcus xylosus strains, although strains from other CNS species also have potential for application. However, it is not entirely clear how the fitness of alternative starter cultures within a fermented meat matrix compares to conventional ones and how this may be affected by processing conditions. Therefore, the aim of this study was to assess the influence of two key processing conditions, namely temperature and acidity, on the competitiveness of a cocktail of five different strains of CNS belonging to species that are potentially important for meat fermentation (Staphylococcus xylosus 2S7-2, S. carnosus 833, Staphylococcus epidermidis ATCC 12228, Staphylococcus equorum DFL-S19, and Staphylococcus saprophyticus FPS1). To this end, fermented meat models consisting of cured meat batters with initial pH values of 5.3, 5.5, or 5.7 were inoculated with these strains, stuffed in containers, and incubated at 23, 30, or 37 °C. Both the pH level and the temperature influenced the composition of the CNS communities, giving a competitive advantage to the best adapted species. Staphylococcus xylosus preferred low temperature and mild acidity, whereas an elevated temperature selected for S. epidermidis and a low pH for S. carnosus. Under the conditions tested, S. saprophyticus and S. equorum were outcompeted by the three other CNS species. Hence, CNS communities in fermented meats are not only established based on the initial presence of specific species in the meat batter but also by their subsequent adaptation to the processing conditions during fermentation, potentially overruling the use of starter cultures.