Process and Quality Control Procedures

8 Microbial Testing

Routine cheese microbial analyses should include yeast and molds, Salmonella sp.,  Staphylococcis aeurius,  Listeria sp. and Eshericia coli. Raw milk cheese of some varieties should be considered higher risk and in some cases cheese made from heat treated but not pasteurized milk must also be considered higher risk. Microbial analyses should be performed near the time of retail sale and, preferably also at the time of manufacture.  A positive test for any species of Listeria should be followed up with specific tests fro Listeria monocytogenes.  Similarly, substantial numbers of  E. coli  or Staphylococcus aureus should be followed up with tests for Enterophathogenic E. Coli or coagulase positive Staphylococcus aureus, respectively. Cheese whey should be monitored for the presence of specific for the culture currently in use.

 

Table 8.1. List of Standards for Dairy Products. Fluid cow's milk products, except creams, shall have a freezing point of -0.508°C or lower.

Product Bacteria n c m M
Cheese (pasteurized milk) S. aureus
E. coli
5 2 100 10,000 (/g)
1,000 (/g)
Cheese (unpasteurized milk) S. aureus
E. coli
5 2 100 10,000 (/g)
1,000 (/g)
Cheese (pasteurized) without ripening, including fresh cheeses, lactic curd with a minimum of 50% moisture Coliform 5 2 100 100 (/g)
Fermented dairy products (e.g. buttermilk, yogourt, sour cream) Coliform 5 2 100 100 (/g ou ml)
Pasteurized milk, cream and other non-fermented dairy products Mesophilic aerobic bacteria (32°C)
Coliform
5
5
2
2
10,000
1
25,000 (/ml)
10 (/ml)
Frozen dairy products Mesophilic aerobic bacteria (32°C)
Coliform
5
5
2
2
10,000
10
50,000 (/ml)
100 (/ml)
Butter Mesophilic aerobic bacteria (32°C)
Coliform
5
5
2
2
10,000
10
50,000 (/g)
100 (/g)
Milk powders and other dairy product powders Mesophilic aerobic bacteria (32°C)
Coliform
5
5
2
2
10,000
10
50,000 (/g)
100 (/g)
Evaporated, sweetened and condensed milk Shall be commercially sterile

Adapted from the Canadian Dairy Information Centre (1997), amended July 2005.

n=number of sample units (subsamples) to be examined per lot
c=maximum number of sample units (subsamples) per lot that may have a bacterial concentration higher than the value for “m” without violation of the Regulations.
m=maximum number of bacteria per g or ml of product that is of no concern (acceptable level of contamination)
M=maximum number of bacteria per g or ml of product, that if exceeded by any one sample unit (subsamples) renders the lot in violation of the Regulations

 

The Canadian Food And Drug Act and Regulations defines acceptable limits for several pathogens in cheese made from pasteurized milk and for cheese made from raw or unpasteurized milk. The limits for cheese made from pasteurized milk per g of cheese are: 500 coliform bacteria, 100 Escherichia coli, and 100 coagulase positive Staphylococcus aureus. The permitted numbers per gram of raw milk cheese are  5,000 coliforms, 500 Escherichia coli, and 1,000 coagulase positive S. aureus. The tolerance for Listeria monocytogenes in cheese and any other ready to eat product is zero.

 

Table 8.2. Microbiological Limits for Dairy-Cheese, Hard. Ex. Parmesan, aw<0.95 and pH<5.6. All cheeses are made with pasteurized milk.

Criteria & EMP
Target Microorganism
Microbiological Limit Recommended Action if Limit is Exceeded Comments
Routine Non-Routine
Coliforms <100/g Investigate, implement corrective action
E. coli (generic) <10/g Investigate, implement corrective action; if >100/g, reject lot
Listeria spp. (EMP) Negative for Zone 2 or 3 Investigate, consider Zone 1 and finished product testing, implement corrective action
Listeria spp. (product) Negative in 25 g Reject lot May be in-process vat sample due to the aging process for natural cheese
Salmonella Negative in 275 g Reject lot May be in-process vat sample due to the aging process for natural cheese
S. aureus 100/g Investigate Test for toxin if slow acid development; if positive for toxin, destroy product

Adapted from Wisconsin Association for Food Protection (WAFP) (2018).

Table 8.3. Microbiological Limits for Dairy-Cheese, Soft, Semi-Soft, Surface-Ripened. Ex. Brie, Fresh Mozzarella, aw>0.95 and pH>5.4. All cheeses are made with pasteurized milk.

Criteria & EMP
Target Microorganism
Microbiological Limit Recommended Action if Limit is Exceeded Comments
Routine Non-Routine
Coliforms <100/g Investigate, implement corrective action
E. coli (generic) <10/g Investigate, implement corrective action; if >100/g, reject lot
Listeria spp. (EMP) Negative for Zone 2 or 3 Investigate, consider Zone 1 and finished product testing, implement corrective action
Listeria spp. (product) Negative in 125 g Reject lot 125-g analytical unit composed of 5 x 25-g samples
Salmonella Negative in 375 g Reject lot
S. aureus 100/g Investigate, implement corrective action.
If ≥10^4 /g, reject lot due to potential for enterotoxin production
Test for toxin if slow acid development; if positive for toxin, destroy product

Adapted from Wisconsin Association for Food Protection (WAFP) (2018).

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