PO24 | DYNAMICS OF COAGULASE-POSITIVE STAPHYLOCOCCI IN ARTISANAL RAW MILK CHEESE: INFLUENCE OF PH

Thomas Dalmonte, Gulnara Guluzade, Serena Giacomozzi, Yitagele Terefe Mekonnen, Ilgar Abdullayev, Chiara Oliveri, Federica Savini, Andrea Serraino, Alessandra De Cesare | DIMEVET, University of Bologna, Italy.

Aim. The aim of this study was to assess the influence of pH on the dynamic of coagulase-positive staphylococci (CPS) counts along the production process of an artisanal raw milk cheese.

Materials and Methods. Coagulase-positive staphylococci were enumerated in 144 samples through a longitudinal sampling of 12 batches of raw milk cheese produced at the same processing plant, using raw milk supplied by two dairy cattle farms. The samples tested were raw milk (n=12) and raw milk cheese after 7 (C7) (n=12), 45 (C45) (n=12) and 90 (C90) (n=12) days of ripening. All samples were analyzed in triplicate. To model the concentration of CPS in raw milk cheese, a frequentist zero-inflated gamma generalized linear mixed model (GLMM), fitted by maximum likelihood, was developed.

Results. CPS in raw milk ranged between 0.3 and 2.1 Log CFU/ml and in raw milk cheese after 90 days of ripening between 0.4 and 2.7 Log CFU/g. The pH values in raw milk ranged between 6.62 and 6.99, at C7 between 5.04 and 5.44, at C45 between 5.08 and 5.43, at C90 between 3.94 and 5.63. The model outputs showed that the initial coagulase-positive staphylococci concentration in raw milk represents the primary driver influencing the dynamics of coagulase-positive staphylococci counts throughout the production process, up to the end of ripening period. The model further showed that a one unit increase in pH during production resulted in a 16.73% increase in coagulase-positive staphylococci Log10 counts in the overall production.

Conclusions. The outputs of the model highlight the critical importance of monitoring the coagulase-positive staphylococci counts in raw milk and the cheese pH to limit the growth of coagulase-positive staphylococci throughout the raw milk cheese production process.
Funding: This study has been funded by the Italian Ministry of Agriculture, Food Sovereignity and Forests under the Contratto di Filiera, Stalla modello, DMI n. 0673777 del 22/12/2021, V Avviso n. 0182458 del 22/04/2022 e s.m.