Microbial Safety Study of Sous Vide


Microbial Safety Study of Sous Vide


  16/09/2019 10:55:33

What is sous vide?
Sous vide, French for “under vacuum”, is a process of cooking in vacuumised plastic pouches under precisely controlled time and temperature conditions, usually via submersion in a water bath.

Why cook sous vide?
Vacuum packaging removes air and seals the food within the heat-stable pouch, resulting in a reduced oxygen or anaerobic environment.  This facilitates efficient heat transfer to the food product and can increase the shelf-life of the product by limiting the growth of spoilage microorganisms.  Sealing the food product also reduces the risk of post-cooking contamination and prevents evaporative loss of moisture.  The precise temperature control of sous vide regimes, improves reproducibility and offers greater control of final product taste and texture in comparison with traditional cooking techniques.

Microbial safety of sous vide
Sous vide processed foods can be broadly classified according to heat treatment:

Lightly processed – heat treatment is insufficient for microbial inactivation; survival of vegetative pathogens and parasites present in the raw food product is probable.  The survival of these organisms considerably limits shelf life, therefore the microbiological quality of the raw product is critical.  Safety should be assessed on a case-by-case basis

Processed at 70°C for 2 min (or equivalent)– based on a 6 log inactivation of Listeria monocytogenes, considered the most heat resistance of the vegetative foodborne pathogens which can also survive and grow at refrigeration temperatures.  Shelf life of these products is limited to 10 days, as the restriction of oxygen and lack of microbial competition provides a favourable environment for psychrotrophic anaerobic spore forming organisms, such as non-proteolytic Clostridium botulinum and psychotrophic B. cereus.

Processed at 90°C for 10 min (or equivalent)– based on a 6 log inactivation of spores of non-proteolytic C. botulinum. Required for extended shelf life (>10 days) cook chill foods.

Cooked – cooked to acceptable taste, texture and appearance but may not be pasteurised.  These treatments are most likely encountered in home sous vide, restaurants and within the wider catering industry.  This includes a wide variety of time-temperature heat treatments.   

Sous vide methods are increasingly used within restaurants and the catering industry.  Where the time/temperature combinations deviate from traditional pasteurisation, there may be implications for the safety of the food product, highlighting the significance of understanding the ability of foodborne pathogens to survive lower temperature cooking processes.  Although temperature/time combinations have been established for temperatures between 60 and 69oC, microbial inactivation data is insufficient at sub 60oC.

When assessing the safety of sous vide cooking at temperatures below 60˚C, the main pathogen of concern is Listeria monocytogenes as this organism demonstrates the most heat resistance of the vegetative foodborne pathogens and can survive and grow at refrigeration temperatures.  This is especially relevant for cook-chill sous vide, which involves refrigerated storage and potential heat regeneration following the cook stage. 
For cook-serve sous-vide regimes, where the food product is either served immediately following sous vide cook, or rapidly chilled, stored and consumed within 2 days; Salmonella, and verocytotoxigenic Escherichia coli are of primary concern. Furthermore, temperatures below 55°C could promote spore germination and subsequent growth of Clostridium perfringens and Bacillus cereus. Therefore the increased risk of foodborne illness with these organisms need to be considered in products cooked this way.

QIB Extra recently completed a short research project determining current sous vide practices in Ireland and their safety. Results are to be made available after project evaluation which is likely to be concluded late 2019/early 2020. A link to these results will be available on this site when ready. 

Do you have a simaliar project that you would like to talk to QIB Extra about? Contact us on +44 (0) 1603 255 342 or info@qibextra.co.uk

 


 

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