Cheddar cheese was made by the stirred-curd procedure from pasteurized milk inoculated with Salmonellea typhimurium and with a slow acid-producing strain of Streptococcus lactis. The Most Probable Number technique was used to enumerate salmonellae in milk and in cheese during its manufacture and ripening. Salmonellae grew rapidly during manufacture and limited additional growth occurred in cheese during the first week of ripening at 13 C after which there was a gradual decline in population. Salmonellae survived during ripening for up to approximately 7 months at 13 C and 10 months at 7 C. Cheese made in 2 of 5 trials exhibited a limited increase in number of salmonellae during the first 2 weeks at 7 C followed by a decline in population of these bacteria. Other cheeses held at 7 C exhibited a reduction in number of viable salmonellae without the initial increase. Growth of salmonellae during the early stages of ripening and subsequent extended survival of these organisms may, in part, be attributable to high moisture (average 43.2%) and high pH (5.75 after overnight pressing) of the cheese which resulted from use of a slow acid-producing starter culture.
1Published with the approval of the Director of the Research Division of the College of Agricultural and Life Sciences, University of Wisconsin.