Brucella melitensis Survival During Manufacture of Ripened Goat Cheese at Two Temperatures

The aim of the current work was to assess the influence of two temperatures, 4°C and 24°C, on pH and water activity and their association with Brucella melitensis survival during the traditional manufacture of ripened goat cheese. Raw milk from a brucellosis-free goat herd was used for the manufacture of ripened cheese. The cheese was inoculated with 5×10⁹ of the B. melitensis 16M strain during the tempering stage. The cheeses were matured for 5, 20, and 50 days at both temperatures. To assess Brucella survival, the pH and a_w were recorded at each stage of the process (curd cutting, draining whey, immersion in brine, ripening I, ripening II, and ripening III). B. melitensis was detected at ripening stage III (1×10³ colony-forming unit [CFU]/mL) from cheeses matured at 4°C with a pH of 5.0 and a_w of 0.90, and at a ripening stage II (1×10⁴ CFU/mL) from cheeses ripened at 24°C with a pH of 4.0 and a_w of 0.89. The remaining stages were free from the inoculated pathogen. In addition, viable B. melitensis was recovered in significant amounts (1–2×10⁶ CFU/mL) from the whey fractions of both types of cheese ripened at 24°C and 4°C. These results revealed the effects of high temperature (24°C vs. 4°C) on the low pH (4) and a_w (0.89) that appeared to be associated with the suppression of B. melitensis at the early stages of cheese ripening. In the ripened goat cheeses, B. melitensis survived under a precise combination of temperature during maturation, ripening time, and a_w in the manufacturing process.