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TOTAL PLATE COUNT

Definition

(quote: Swiss Handbook of Foods / ISO 4833:2003)

 

The total plate count TPC (aerobic, mesophilic organisms) defines how many aerobic (oxygen-loving), mesophilic (moderate-temperature-loving) micro-organism colonies such as bacteria, yeast and mould fungi will grow in 72 hours on an agar plate that was normed for microbiological testing at a controlled temperature of 30 °C.

 

Determination

Precisely defined amounts of the sample will be mixed in petri dishes with nutrient solution and kept in an incubator at 30 °C. After 3 days, the colonies grown on the samples will be counted, thereby determining the number of aerobic, mesophilic organisms per g or per ml of sample.

The result will be given in colony forming units (cfu/g or cfu/ml).

 

Application

Apart from the undesirable, pathogen organisms, the total plate count or plate count also includes the desirable micro organism such as lactic acid bacteria in fermented foods (yoghurt or cheeses). The count of aerobic, mesophilic organisms can therefore be used to determine the hygienic status of these foods.

 

A high total plate count generally points to a poor microbial quality of a non-fermented product. For specific details, further tests will have to be done.

 

However, drawing the reverse conclusion is not that simple, as it does not necessarily mean that a product with a low total plate count is good - for determining that, further testing of indicator organisms is needed.

 

 

Guideline values for a few products

  Guideline value Notes
Chocolate 50’000 cfu/g  
Smoked salmon 100’000 cfu/g  
Ice-cream sold by scoop 100’0000 cfu/g not counting lactic acid bacteria
Instant products 100’000 cfu/g  
Mixed salad packaged 10’000’000 cfu/g  
Dried fruit 10’000 cfu/g  
Ravioli, tortellini packaged 1’000’000 cfu/g including lactic acid bacteria
Butter 100’000 cfu/g  
Margarine 1’000 cfu/g  
Pasteurized milk 100’000 cfu/g  
UHT milk 100 cfu/g after 15 days at 30 °C
Whipped cream 1’000’000 cfu/g including  lactic acid bacteria
Refined oils and fats 10 cfu/g  

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