This section covers the ACMSF’s views and recommendations for the control of non-proteolytic Clostridium Botulinum in chilled vacuum packed and modified atmosphere packed foods.
Further information can be found in Food Standards Agency guidance, which summarises ACMSF advice, on the hazards and controls associated with vacuum and modified atmosphere packed chilled foods. The guidance is essential reading for small businesses and local authority environmental health officers.
The ACMSF has recommended control factors to prevent the growth of non-proteolytic Clostridium botulinum in chilled foods where the organism has not been eliminated or is not sufficiently controlled by some other factor. The committee recommends that food manufacturers, caterers and retailers should take account of the time it takes for the organism to grow and/or produce toxin at the actual temperatures the food is expected to encounter during its shelf-life. This must take into account storage, transport, distribution, retail, catering and domestic stages, as appropriate.
It is recognised that certain bulk vacuum packaged foods are stored for a period under strictly-controlled conditions at temperature between -2ºC and 0ºC. These temperatures are sufficient to prevent growth and toxin production by non-proteolytic Clostridium botulinum.
However, the ACMSF does not believe it is realistic to maintain temperatures of 3ºC or less consistently during all the parts of the chill chain. The committee also does not believe it is acceptable to rely on chill temperatures as the only method of preventing growth of non-proteolytic strains of Clostridium botulinumin chilled foods that have an assigned shelf-life of more than ten days.
In addition to chill temperatures of less than 8ºC, the ACMSF recommends that prepared chilled foods with an assigned shelf-life of more than ten days should contain one or more controlling factors at levels that prevent growth and toxin production by strains of non-proteolytic Clostridium botulinum.
Growth and toxin production by non-proteolytic Clostridium botulinum have been studied under a range of conditions. The only evidence for growth and toxin production by non-proteolytic Clostridium botulinum below 10ºC in less than ten days are in laboratory experimentation conditions, which are extremely unlikely to be found in foods. However, products with an assigned shelf-life of less than ten days must not be stored above 8ºC – this is the statutory maximum temperature specified in the temperature control regulations (subject to the requirements and exemptions of the Food Hygiene (England) Regulations 2006 or their equivalent in Scotland, Wales and Northern Ireland).
The ACMSF believes that there is minimal risk of toxin production by non-proteolytic Clostridium botulinum in chilled foods stored below 10ºC with an assigned shelf-life of less than ten days.
The ACMSF recommendation of storing below this temperature predates the introduction of the temperature control regulations and the statutory maximum temperature.
There are two key ACMSF recommendations that relate to the safety of vacuum packed food products.
Firstly, for products with a shelf-life of more than ten days:
- In addition to chill temperatures, the following control factors should be used singly or in combination to prevent growth of non-proteolytic Clostridium botulinum:
- a heat treatment of 90ºC for ten minutes or equivalent
- a pH of 5 or less
- a minimum salt level of 3.5% (in the aqueous phase)
- an aw of 0.97 or less
- a combination of heat and preservative factors shown to prevent growth
Secondly:
- In the absence of demonstrated safety factors, shelf-life must be restricted to less than ten days and the product must be stored at 8ºC or below (see note below).
Note: The ACMSF’s original recommendation, refers to a temperature of 10ºC, which predates the introduction of the temperature control regulations. The statutory maximum temperature is 8ºC (subject to the requirements and exemptions of the Food Hygiene (England) Regulations 2006 or their equivalent in Scotland, Wales and Northern Ireland).
The ACMSF recommended that a comprehensive and authoritative code of practice should be developed for the manufacture of vacuum packed or modified atmosphere packed chilled foods, with particular regard to the risks of botulism.
This task was given to Campden BRI, which published ‘A code of practice for the manufacture of vacuum packed and modified atmosphere packed chilled foods’ (Guideline No.11) in 1996 and updated in 2009.
Copies of the guidelines are available from the Campden BRI website via the link below. Please note that the publication is not free. Campden BRI members can buy the guidelines at a reduced (members) rate.
See the guide, available from the Campden BRI website, which provides advice to assist manufacturers with the safe production of vacuum packaged and modified atmosphere packaged food product.
A food business operator that applies a shelf-life of more than ten days to its products must be able to demonstrate to the local competent food authority how the company is controlling the potential hazard of non-proteolytic Clostridium botulinum growth, based on the ACMSF’s recommendations.
If the food business operator is unable to demonstrate these control factors, the product’s shelf-life must be restricted to less than ten days at storage and display temperature of ≤ 8ºC.
The practical application of these control measures are considered in Module 3.
Different foods will vary in their inherent risk with respect to Clostridium botulinum and as a result their priority for enforcement attention. For example, hot smoked fish would have a greater inherent risk relative to a hard cheese like cheddar. The importance of recognising the different risks is considered further in Module 3 and Module 4.
The 1992 ACMSF report contains further examples and details of inherent risk in respect of Clostridium botulinum. See Table 12 of the report or see an adapted version in Module 4 - Section 3.
The ACMSF report identifies three categories of products in respect of inherent risk:
The basis for these categories and relevance for enforcement officers is discussed in Module 3 and Module 4.
Industry guidance, produced by Campden BRI, also contains a table of examples of inherent risks. See Table 1 in ‘A code of practice for the manufacture of vacuum packed and modified atmosphere packed chilled foods’ (Guideline No. 11) on the Campden BRI website via the link below. Please note that the publication is not free. Campden BRI members can buy the guidelines at a reduced (members) rate.
See Table 1 in ‘A code of practice for the manufacture of vacuum packed and modified atmosphere packed chilled foods’ (Guideline No. 11) on the Campden BRI website.