Staphylococcus aureus growth and enterotoxin production during the manufacture of uncooked, semihard cheese from cows' raw milk.
Staphylococcus aureus growth and enterotoxin production during the manufacture of model Saint-Nectaire, Registered Designation of Origin Saint-Nectaire, and Registered Designation of Origin Salers cheeses, three types of uncooked, semihard, raw milk cheese, were investigated. Coagulase-positive staphylococci (SC+) grew rapidly during the first 6 h. Between 6 and 24 h, counts increased by less than 0.5 log CFU/ml. Raw milk counts ranged from undetectable (<10 CFU/ml) to 3.03 log CFU/ml. Maximal levels reached in cheese on day 1 ranged from 2.82 to 6.84 log CFU/g. The level of SC+ after 24 h was mainly influenced by the milk baseline SC+ level (correlation coefficient, r > 0.80) but pH at 6 h influenced the SC+ growth observed between 6 and 24 h (r > 0.70). Thus, the initial level of SC+ in raw milk should be maintained below 100 CFU/ml and best below 40 CFU/ml. To limit growth, acidification should be managed to obtain pH values around or below 5.8 at 6 h in Saint-Nectaire cheeses and around or below 6.3 at 6 h in Salers cheeses. Enterotoxins were only detected in two Salers cheeses whose SC+ counts on day 1 were 5.55 log CFU/g and 5.06 log CFU/g, respectively, and whose pH values at 6 h were high (approximately 6.6 and 6.5, respectively).
Delbes
Celine
C
IINRA, Unité de Recherches Fromagères, Aurillac, F-15000, France. cdelbes@clermont.inra.fr
Alomar
Jomaa
J
Chougui
Nadia
N
Martin
Jean-François
JF
Montel
Marie-Christine
MC
D000818:Animals; D002417:Cattle; D002611:Cheese / Q000382:microbiology*; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D004768:Enterotoxins / Q000096:biosynthesis*; D005516:Food Microbiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008892:Milk / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000254:growth & development* / Q000378:metabolism*; D013696:Temperature; D013997:Time Factors
D004768:Enterotoxins