Growth of Staphylococcus aureus, staphylococcal enterotoxin formation, and the effect of scalding temperature during the production of Alpine cheese in a laboratory cheese-making model.

To reduce the number of potential S. aureus contaminated cheese reaching consumers, European legislation stipulates that all cheese must be tested for coagulase-positive staphylococci (CPS) at the point in production when numbers are expected to be highest. If CPS counts exceed 105 CFU/mL, enterotoxin tests must be conducted. In the case the enterotoxin test shows positive results the cheese must be destroyed. Manufacturers of Swiss Alpine cheese are exempt from this legislation because enterotoxin formation in hard cheese is expected to be very unlikely, given the high scalding temperatures the cheese is exposed to during its production. Such temperatures result in inactivation of CPS in the curd. However, this assumption has not yet been scientifically demonstrated. Therefore, a laboratory-scale cheese production experiment was performed, in which the conditions corresponded with certain limitations to practical cheese-making conditions in terms of temperature and time exposure like in Gruyere or Tete de Moine Swiss type cheese. Raw milk aliquots (200 ml) were inoculated with five different strains of CPS, and scalding temperatures, ranging from 46-56° C, were applied during cheese production. The temperatures applied after pressing the curd aimed at reproducing the temperature curve in the peripheral zone of a real cheese wheel. Contrary to expectations, enterotoxin formation occurred and changed with the different scalding temperatures (52-56° C).The differences in enterotoxin formation were more associated with strain type rather than temperature. Based on these results, the mechanism of enterotoxin formation in cheese requires further study.