Factors affecting the viability of Staphylococcus aureus and production of enterotoxin during processing and storage of white-brined cheese

摘要

Staphylococcus aureus is a major foodborne pathogenthat causes severe disease in humans. It is commonlyfound in milk and dairy products, particularly in freshbrined cheese. Our aim was to investigate the behaviorof Staph. aureus and enterotoxin production during thestorage of white-brined cheese prepared with or withouta starter culture and stored in a 10 or 15% NaCl brineat 10°C and 25°C for 28 d. NaCl concentration, wateractivity, pH, and number of Staph. aureus and lacticacid bacteria were determined in cheese and brine.Only 1 of 4 Staph. aureus strains (ATCC 439) was positivefor enterotoxin production, and its production wasdetected in unsalted UHT milk, but not in salted milkor in any of the cheese treatments held at 37°C for1, 3, or 7 d. Staphylococcus aureus grew in the cheesestored in both brines at 10°C and 25°C, regardless ofthe presence of a starter culture, although the lattersignificantly reduced Staph. aureus growth in cheese orits brine at 10°C. Staphylococcus aureus numbers wereincreased by 2.26 and 0.47 log_(10) cfu/g in cheese storedin 10 and 15% NaCl brine, respectively, in the presenceof starter culture, and by 2.78 and 2.96 log_(10) cfu/g,respectively, in the absence of starter culture at 10°C.Nonetheless, the pathogen grew, but at a lower numberin the brines. The salt concentration of cheese storedin 10% brine remained at approximately 5% duringstorage; however, in 15% brine, the salt concentrationincreased to almost 8% (wt/wt) by 28 d. The additionof a starter culture, high salt concentration, low temperature,and pH (～5.2) had inhibitory effects on thegrowth of Staph. Aureus. Moreover, lactic acid bacterialnumbers increased considerably in cheese and brineby d 28. The use of starter cultures, salt (15%), andlow storage temperature (10°C) reduced the growth ofStaph. Aureus, and salt may have prevented enterotoxinproduction in white-brined cheese.