The 1992 ACMSF report discusses these and other pathogens that may be present in the raw materials used in preparing chilled foods or that may contaminate foods during processing.
This is a general environmental contaminant and traces may be found on virtually all raw agricultural products and many processed ones.
It is generally regarded to be of particular concern in chilled foods because of its ability to grow at temperatures close to freezing and survive/grow under a wide range of pH and aw values.
For information on pH and aw, see Module 3
Control of listeria is achieved by a variety of techniques:
- heating at 70ºC for two minutes, or an equivalent heat process
- selecting and disinfecting raw materials to reduce the number and incidence of contamination
- using high care areas in the manufacture of foods to reduce the risk of contamination of cooked material
- limiting the shelf-life of products
This is a non spore-forming organism that grows as low as temperatures of -1ºC. Yersinia will grow well in vacuum packaged products, particularly in the absence of any other controlling factors.
This bacterium can be found everywhere and is a common contaminant of vegetable and dairy products. Most strains do not grow below 10ºC. However, there have been reports that some strains can grow at temperatures as low as 4ºC and can produce toxin at 8ºC.