Survival of a Five-Strain Cocktail of Escherichia coli O157:H7 during the 60-Day Aging Period of Cheddar Cheese Made from Unpasteurized Milk
Abstract:The U.S. Food and Drug Administration Standard of Identity for Cheddar cheeses requires pasteurization of the milk, or as an alternative treatment, a minimum 60-day aging at ≥2°C for cheeses made from unpasteurized milk, to reduce the number of viable pathogens that may be present to an acceptable risk. The objective of this study was to investigate the adequacy of the 60-day minimum aging to reduce the numbers of viable pathogens and evaluate milk subpasteurization heat treatment as a process to improve the safety of Cheddar cheeses made from unpasteurized milk. Cheddar cheese was made from unpasteurized milk inoculated with 101 to 105 CFU/ml of a five-strain cocktail of acid-tolerant Escherichia coli O157:H7. Samples were collected during the cheese manufacturing process. After pressing, the cheese blocks were packaged into plastic bags, vacuum sealed, and aged at 7°C. After 1 week, the cheese blocks were cut into smaller-size uniform pieces and then vacuum sealed in clear plastic pouches. 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°C decreased less than 1 and 2 log, respectively. These studies confirm previous reports that show 60-day aging is inadequate to eliminate E. coli O157:H7 during cheese ripening. Subpasteurization heat-treatment runs were conducted at 148°F (64.4°C) for 17.5 s on milk inoculated with E. coli O157:H7 at 105 CFU/ml. These heat-treatment runs resulted in a 5-log E. coli O157: H7 reduction.
Document Type: Research Article
Affiliations: 1: National Center for Food Safety and Technology, Food and Drug Administration, Moffett Campus, Summit-Argo, Illinois 60501, USA 2: National Center for Food Safety and Technology, Illinois Institute of Technology, Moffett Campus, Summit-Argo, Illinois 60501, USA 3: Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, Maryland 20740, USA; Food Safety Inspection Service USDA, Washington, D.C. 20050, USA 4: National Center for Food Safety and Technology, Illinois Institute of Technology, Moffett Campus, Summit-Argo, Illinois 60501, USA; Cerebos Paci?c Limited R&D Division, Singapore 048423
Publication date: May 1, 2006
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