Inhibition of Staphylococcus aureus Growth and Enterotoxin-A Production in Cheddar Cheese Produced with Variable Starter Activity

Abstract

Twelve cheese batches were made with variable starter activity, from milk inoculated with Staphylococcus aureus. At the end of cheddaring, only half the curd of each batch was salted and each portion was then pressed separately, cut and stored at 11 and 4 C for 6 weeks. Changes in bacterial counts, pH, enterotoxin A concentration and organoleptic properties were monitored. At the end of cheddaring, enterotoxin was detected in batches made with large initial inocula of S. aureus and/or low starter activities. At the end of pressing, the count of S. aureus, pH and enterotoxin concentration in the unsalted cheese (USC) were significantly lower than in salted cheese (SC), due to the adverse effect of salting on growth of microorganisms other than S. aureus. No change in enterotoxin concentration was detected in USC during storage at 11 and 4 C, and a sharp decline in S. aureus count occurred. The rate of such decline at 11 C exceeded that at 4 C. Increases in S. aureus count and enterotoxin concentration occurred in some SC batches stored at 11 C, whereas a slight decrease in S. aureus count and no change in enterotoxin concentration occurred in all SC stored at 4 C. At the end of storage, no cheeses had gas defects or significant flavor defects, which could have prohibited further processing.