U.S. Food and Drug Administration Center for Food Safety and Applied Nutrition

Three Year Research Plan
National Food Safety Initiative
Produce and Imported Foods Safety Initiative
2000-2002 Update
May 2001

Project No. 13: Survival of Food Pathogens During the 60-Day Aging Period of Hard Cheeses Made from Unpasteurized Milk

(Table of Contents)

CFSAN Regulatory Codes: V.A.1
CFSAN Program Priority Code:
Start Date: 10/98    Completion Date: 9/20/02

Statement of Research Problem:
Research is needed to assess whether the 60-day aging process of cheese made from unpasteurized milk is adequate to eliminate foodborne pathogens. Cheddar cheese will be made from milk inoculated with food pathogens (Escherichia coli O157:H7 or S. typhimurium DT 104). Food pathogen levels will be monitored during the cheese making and aging period. Heat treatment of 64.4 °C for 16s in combination with 60-day aging will also be evaluated. The data will be incorporated into microbial risk assessment models to assist in validating that the control measures used in the cheese making practice provide an adequate level of public health protection.

Statement of Project Objective(s):

  1. Evaluate adequacy of the minimum aging period of hard cheeses made from unpasteurized milk to eliminate food pathogens.
  2. Evaluate and validate alternative/improved methods to provide the desired level of public health protection.
  3. Validate techniques to monitor and control and processing conditions used in the manufacture of hard cheeses.

Anticipated Impact on FDA Regulatory Program:
In the event that 60-day aging is found to be inadequate to provide the appropriate level of public health protection, an evaluation of alternative control measures would assist the agency in the development of policy in this area. Validation of the effectiveness of current or alternative process control measures used in the manufacture of aged hard cheese would result in a greater assurance of a safe food supply and enhanced public confidence in these products.

Project Priority Changes During FY2000:
Work on E. coli O157:H7 survival in unpasteurized milk cheese is being continued. Three to five-strain cocktail of E. coli O157:H7 have been inoculated into the unpasteurized whole milk to give a final cell concentration of 105-6 cells per mil. Work on L. monocytogenes survival in unpasteurized milk cheese has been dropped because of the need to focus on running lower levels of E. coli O157:H7. Levels of E. coli O157:H7 will be inoculated into the unpasteurized whole milk to give a final cell concentration of 103-4cells per ml.

 Project Associated Personnel Administrative Liaison(s): Dave Armstrong: 708/728-4108

Research Personnel:
Name Office/Division FTE [00, 01, 02] Component
J. E. Schlesser OPDFB/DFFP 0.8, 0.8, 0.8 1
 
Total FDA FTE's:  
0.8, 0.8, 0.8  
Non-FDA NCFST scientist support   2.0, 2.0, 2.0 1
Collaborators: David Henning/South Dakota State Univ.; Mohammad Modarres/University of Maryland

 Component 1: <single component project>
Component 1 Objectives:
  1. Evaluate adequacy of the minimum aging period of hard cheeses made from unpasteurized milk to eliminate food pathogens.
  2. Evaluate and validate alternative/improved methods to provide the desired level of public health protection.
  3. Validate techniques to monitor and control the processing conditions used in the manufacture of hard cheeses.
Component 1 FY 2000 Deliverables:
  1. Produce cheese made from unpasteurized milk inoculated with E. coli O157:H7.
  2. Monitor the food pathogen levels during the cheese making process and the aging period.
Component 1 Progress:
Pilot plant cheese making equipment was installed into the NCFST bio-safety level II (BSL-II) to conduct research using food pathogens on the pilot plant scale. Standard operation procedures were developed and validated for working with pathogens in the BSL-II lab. Procedures for sampling of cheese, and enumeration of coliforms, total bacterial counts, and pathogens were developed. A five-strain cocktail of E. coli O157:H7 was inoculated into the unpasteurized whole milk to give a final cell concentration of 105 cells/ml. Freshly made cheeses containing the food pathogen were packaged into plastic bags, sealed with a vacuum-packaging machine, and aged at 7 °C. During aging, cheese samples were sampled for enumeration of coliforms, total bacterial counts, and pathogens on nonselective and selective media. The initial cheese trials showed a 1 to 2-D reduction by day 60.
Technical Barriers to Meeting Component 1 Objectives or Deliverables:
During the milling step of a cheese run, aerosol production was noted. The milling process was modified. After modification, containment of the aerosol was shown. SOP training with surrogates had to be completed before pathogen runs could be resumed.
Component 1 FY 2001 Deliverables:
  1. Produce cheese made from unpasteurized milk inoculated with E. coli and heat-treated at 64.4 °C for 16s.
  2. Monitor the food pathogen levels during the cheese making process and the aging period.
  3. Produce cheese made from unpasteurized milk inoculated with S. typhimurium DT 104 and heat-treated at 64.4 °C for 16s (Henning).
  4. Validate techniques to monitor and control the processing conditions used in the manufacture of Cheddar cheese.
Component 1 FY 2002 Deliverables:
  1. Validate techniques to monitor and control the processing conditions used in the manufacture of Cheddar cheese.
  2. Incorporate data into microbial risk assessment models to assist in validating that the control measures used in the cheese making practice provide an adequate level of public health protection.

FY 2000 Publications Associated with the Project: none listed


Table of Contents

National Food Safety Programs
Foods Home  |  FDA Home  |  Search/Subject Index  |  Disclaimers & Privacy Policy  |  Accessibility/Help

Hypertext updated by jms/dav 2001-OCT-02