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Microbial risk management: Clostridium botulinum and VP/MAP chilled foods
Project Code: B13006
Betts, R ;
Institute of Food Research Enterprises Ltd
Peck, M; Stringer, S
A substantial quantity of chilled foods has been sold in the UK and overseas in the last two decades, and when correctly stored has not been associated with foodborne botulism. Current practice would therefore appear to have a high degree of safety.
The majority of commercially produced pre-packaged chilled foods have a shelf life greater than 5 days, and some have a shelf life greater than 10 days without receiving any of the control measured specified by the ACMSF (1992). The ACMSF (1995) recommendation of 10 days at 5°C/5 days at 10°C is not adhered to any significant extent in the UK or elsewhere. The 10 day rule at 8°C specified in the 1996 industry code of practice is only adhered to by major producers in the UK and Benelux market. In some countries (e.g. France, Finland), chilled products have been safely produced, over several decades, with shelf lives greater than 10 days. Many of these products will not have received a 6 log non-proteolytic C. botulinum process or any of the other control measured specified by the ACMSF (1992) and their shelf lives take account of lower temperature storage than 8°C.
It is not easy to determine the maximum shelf-life of chilled foods at 8°C (where other controlling factors are not known) on only the data from 1307 independent challenge tests of toxin formation by inoculated non-proteolytic C. botulinum. It is clear that, given the correct circumstances, if present, non-proteolytic C. botulinum is able to form toxin in 10 days or less at 8°C. Also, predictive models indicate that toxin formation can occur in 10 days or less at 8°C (the model in ComBase Predictor estimates toxin formation in 6 days at 8°C). That toxin formation has not occurred in correctly stored short shelf-life chilled foods sold in the UK (and internationally) must be due to presence of one or more “unknown controlling factors”. The difficulty is that the magnitude, variability, and nature of these “unknown controlling factors” is not known, and it is suspected that the magnitude, variability, and nature are not the same for all chilled foods. The position is therefore that while short shelf-life foods have been produced safely in the UK (and internationally) for more than two decades, it is not known why they are safe with respect to foodborne botulism, or what the safety margins are.
Based on the extensive sales of chilled foods without any incidence of foodborne botulism (when correctly stored), current industrial practice (application of GMP, GHP and HACCP principles) would appear to provide a good level of protection. It would seem reasonable, therefore, that current industrial practice be allowed to continue. It is noted that in the UK the majority of commercially produced pre-packaged chilled foods have a shelf life greater than 5 days, and some have a shelf life greater than 10 days without receiving any of the control measured specified by the ACMSF (1992). Consideration should therefore be given to the FSA including *storage at <=8°C and a shelf-life of <=10 days* in their document, rather than *storage at <=5°C and a shelf-life of <=10 days or storage at 5°-8°C and a shelf-life of <=5 days*. It is cautioned, however, that if present, non-proteolytic C. botulinum can form toxin in 10 days and less at 8°C, and there is insufficient clear information as to what the safety margins are in foods as sold, particularly when attempting to take into account the temperature performance of the complete chill chain throughout foods’ shelf lives. It is therefore strongly recommended that extreme caution be used when modifying current industrial practice (e.g. extending the shelf-life of chilled foods over that currently used), and in the development of new products. Since, although current industrial practice appears safe, it is possible that chilled foods could be produced for which a 10 day shelf life at 8°C would not be suitable. It would seem logical to apply this approach to all chilled food sold in the UK.
It was noted in several studies that toxin formation by non-proteolytic C. botulinum was as rapid (or in some circumstances more rapid) in foods packed in air as under VP or low-oxygen MAP. This is presumably because there is no oxygen in the food, i.e. the food is reduced. Packaging under air or a similar oxygen-containing atmosphere is therefore not a guarantee that toxin formation by non-proteolytic C. botulinum will be prevented.
It has been brought to our attention that some chilled VP/MAP foods such as meat may be given a *rolling 10 day shelf-life*. That is, the product is opened during the initial 10 day shelf-life, some is used, and then the remainder is repacked and given a further 10 day shelf-life. Thus, the shelf-life is extended beyond 10 days without the identification of other factors that control toxin formation by non-proteolytic C. botulinum. While we are not aware of this practice leading to outbreaks of botulism, this represents a significant divergence from the guidance and would appear to be a high risk practice. It is therefore proposed that for foods where no other controlling factor can be identified, the maximum shelf-life is 10 days, and that this commences once the product is first vacuum or modified atmosphere packed. The shelf-life must not be restarted if the product is subject to a further packing under vacuum or modified atmosphere, unless other controlling factors (as described by the ACMSF) are applied.
. Improvements in temperature control throughout the chill chain could make a significant contribution to microbiological food safety with respect to foodborne pathogens that are able to grow at chilled temperatures, such as non-proteolytic C. botulinum and Listeria monocytogenes. It is noted that maintenance at a temperature of 5°C was recommended by Richmond in 1991. The chill chain of major UK multiples is targeted at 5°C or below throughout distribution and retail display. In practice, available surveys of all types of UK chilled food outlets (including major multiples, farmers markets, small stores and other outlets) indicated that the average temperature at retail was 4°C-6°C, with 6% of samples at >8°C. In the UK, domestic refrigerators are replaced on average every 8 years, thus the last domestic refrigerator survey that was carried out in 1990 is of date, and needs to be re-run in order to ensure the UK has up to date information on domestic refrigerator temperature performance. The 1990 UK survey found that there was variation in performance between domestic fridges and within each refrigerator over time. Also, different temperatures were recorded in different parts of single refrigerators. The overall mean temperature was 6.6°C, with approximately 9% of the time spent at >9°C. Temperature control in the chill chain appears to be similar in other developed countries.
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