Behavior of Staphylococcus aureus in Cheddar Cheese Made with Sodium Chloride or a Mixture of Sodium Chloride and Potassium Chloride

Abstract

Stirred-curd Cheddar cheese was manufactured from milk artificially contaminated with < 1000 Staphylococcus aureus cells/ml. Lactic starter culture was added to the milk at the rate of 1.0 or 0.5% (v/v). Curds were divided and salted with either NaCl or a mixture of KCl/NaCl to achieve final salt concentrations of approximately 2.4 or 1.2%. Some portions of curd remained unsalted. Cheeses were analyzed for moisture and salt content and were stored at 4 or 10°C for 8 weeks. Bacterial counts and pH values were determined during manufacture and storage of cheeses. Unsalted cheeses had the lowest and the 2.4%-salted cheese had the highest S. aureus counts. Cheeses salted with KCI/NaCl had considerably lower S. aureus and non-S. aureus counts than did cheeses salted with NaCl. All cheeses made with 1.0% starter culture had appreciably lower counts of S. aureus than did cheeses made with 0.5% starter culture. Low levels (0.05 to 0.52 ng/g) of enterotoxin A were found in 16 of 17 samples tested with the radio immunoassay procedure. Presence of enterotoxin was not directly associated with the kind or amount of salt used to produce the cheese.