P3-36 Development of a Decision-making Matrix for Assessing the Shelf Stability of Cheeses

Wednesday, August 3, 2016
America's Center - St. Louis
Wan Mei Leong, University of Wisconsin-Madison, Madison, WI
Steve Ingham, Wisconsin Department of Agriculture, Madison, WI
Barbara Ingham, University of Wisconsin, Madison, WI
Introduction: The FDA Food Code defines foods with pH <4.2 and any aw, or aw <0.88 and any pH as “time/temperature control for safety (TCS) foods.” TCS foods require refrigeration at <5°C, or must be discarded after unrefrigerated storage for >6 h at temperature <21°C. Many cheeses are deemed TCS foods according to Food Code criteria.

Purpose: Our goal was to combine laboratory data and published research to develop a decision-making matrix that could assist industry personnel, retailers, and regulators in assessing suitability of cheeses for extended room temperature storage at retail.

Methods: One hundred two cheeses in sliced forms were challenged with single-pathogen cocktails: Listeria monocytogenes (10 strains), Salmonella spp. (6), Escherichia coli O157:H7 (5), and Staphylococcus aureus (5), at starting concentration ca. 104 CFU/g. Inoculated cheeses were vacuum-packaged and stored at 25°C. Samples were measured for pH and enumerated on selective agars at day 0, 3, 6, 9, 12, and 15. Un-inoculated cheeses were analyzed for % moisture, salt, and titratable acidity. Background flora of inoculated cheeses were determined on day 0, 6, and 15. Survival under temperature cycling (alternating between 4°C and 25°C at every 12 h) and aerobic storage were tested for 35 of 102 cheeses and surviving bacteria enumerated.

Results: Natural cheeses made from pasteurized cow’s milk, with the exception of mold-, bacterial surface-ripened, and Swiss-style cheeses, which meet one of the requirements below, are safe for non-refrigerated storage up to 15 days, at temperatures < 25°C: i) pH ≤ 5.10, ii) pH > 5.10 and % moisture ≤ 39, iii) pH > 5.10 and % salt-in-the-moisture phase ≥ 7.20, or iv) pH > 5.10 and water activity (aw) ≤ 0.95.

Significance: Cheese may be stored at retail for up to 15 days at up to 25°C when a letter guaranteeing cheese pH and either % moisture, % salt-in-the-moisture-phase, or aw accompanies the cheese on shipment to retail establishments.