Effect of temperature and pH on the community dynamics of coagulase-negative staphylococci during spontaneous meat fermentation in a model system

摘要

Coagulase-negative staphylococci (CNS) contribute to the product quality of fermented meats. In spontaneously fermented meats, CNS communities are variable and difficult to predict, as their compositions depend on a superposed combination of different processing factors. To partially disentangle this superposition, a meat model system was used to study the influence of temperature and pH on the CNS community dynamics. Therefore, cured pork mince was prepared that was divided into three batches of different initial acidity levels, namely pH 5.7, pH 5.5, and pH 5.3. These three batches were incubated at three different temperatures, namely 23 degrees C, 30 degrees C, and 37 degrees C. Hence, the experimental set- up resulted in nine combinations of different temperature and initial pH values. Samples were analysed after 3 and 14 days to monitor pH, colony counts, and species diversity of the CNS communities, based on mannitol-salt-phenol-red agar (MSA) medium. At conditions of mild acidity (pH 5.7) and low temperature (23 degrees C), as often encountered during artisan-type meat fermentations, a co-prevalence of Staphylococcus xylosus, Staphylococcus equorum, and Staphylococcus saprophyticus occurred. At the same initial pH but higher incubation temperatures (30 degrees C and 37 degrees C), Staphylococcus lugdunensis became the prevailing CNS species, besides S. saprophyticus (30 degrees C) and the coagulase-positive species Staphylococcus aureus (37 degrees C). When the initial pH was set at 5.5, S. saprophyticus was the prevailing CNS species at both 23 degrees C and 30 degrees C, but it was replaced by Staphylococcus epidermidis and Staphylococcus simulans at 37 degrees C after 3 and 14 days, respectively. At the most acidic conditions ( pH 5.3), CNS counts declined and many of the MSA isolates were of non-staphylococcal nature. Among others, Staphylococcus carnosus (23 degrees C), Staphylococcus warneri (30 degrees C), and S. epidermidis (37 degrees C) were found. Overall, the results of the present study indicated that the processing factors temperature and pH had a clear impact on the shaping of staphylococcal communities during meat fermentation.