Extension Education: Applied Reproductive Management Symposium: Beef and Dairy Cattle Topics

From 1948 to 1988, there were 6 confirmed foodborne disease outbreaks in the U.S. transmitted with domestically produced hard cheeses as the food vehicle. Various research reports have raised concerns about the public health protection provided by the current 60-day aging period in the manufacture of hard cheeses made with unpasteurized milk. The objective of this study was to investigate the adequacy of the 60-day minimum aging to eliminate the foodborne pathogens and evaluate milk thermalization as a process to improve the safety of hard cheeses made from unpasteurized milk. Hard cheese was made from unpasteurized milk inoculated with a five-strain cocktail of acid-tolerant E. coli O157:H7. Samples of unpasteurized milk, curd and whey were collected during the cheese manufacturing process. After pressing, the blocks of hard cheese were packaged into plastic bags, and sealed with a vacuum-packaging machine, and aged at 7 oC. After 1 week, the cheese blocks were cut into smaller uniform-sized pieces, and vacuum sealed in clear plastic pouches for ease of sampling at the various aging intervals. Samples were plated and enumerated for E. coli O157:H7. Populations of E. coli O157:H7 increased during the cheese making operations. Population of E. coli O157:H7 in cheese aged for 60 and 120 days at 7 oC, decreased less than 1 log and 2 logs, respectively. Experiments were conducted at 64.4 oC for 16 seconds on milk inoculated with E. coli O157:H7 at 10 5 CFU/ml. Supply milk and thermalized milk were taken at 0, 45 and 90 minutes to determine the levels of E. coli O157H7. Thermalization runs resulted in a 5-D E. coli O157:H7 reduction.