Response to the FSA consultation on Guidance on the safety and shelf-life of vacuum and modified atmosphere packed chilled foods

Submitted on behalf of IFR by
Prof Mike Gasson and Prof Mike Peck

August 2004

Major comments

Title

Intended user

The document is too broad and too vague for the intended users. Supplementary material (e.g. Table 1) should be removed, and the document must contain “do” and “don’t” rather than “may” and “may not”.

What is Clostridium botulinum?

To avoid misunderstanding about the oxygen content of food (for example, botulism outbreaks have been associated with baked potatoes, and most users of this document might not consider these anaerobic), and since spores germinate under aerobic conditions, revisions are suggested to the section “What is Clostridium botulinum”. This section should read “Clostridium botulinum is a spore-forming, anaerobic bacterium. This bacterium produces a very powerful toxin in the food which causes the serious paralytic illness botulism, a frequently fatal form of food poisoning. Botulinum toxin is the most potent substance known. The spores are widely distributed in the environment, and are also liable to present in food. Toxin is produced when the spores are able to germinate, and then to grow in favourable oxygen-free environments. Such environments frequently occur locally in foods that might not be expected to be depleted of oxygen. For example, outbreaks of botulism have been associated with baked potatoes in aluminium foil. VP/MAP foods are therefore likely to present a suitable growth environment for C. botulinum. Indeed outbreaks of foodborne botulism have been associated with VP/MAP foods, the most commonly implicated food being smoked fish.”

What does the guide cover?

The present document is based on ACMSF advice (1992 and 1995) and it is not consistent with the Code of Practice, since the Code did not include the 1995 ACMSF advice. Thus, the final sentence of this section is incorrect and requires revision. This issue and also others mentioned in this response may need to be considered by the ACMSF.

Mesophilic C. botulinum has led to outbreaks of foodborne botulism following temperature abuse of products intended for chill storage in other countries and indeed is listed as of potential concern in Table 1. Thus the statement “Mesophilic C. botulinum is not considered a risk” on Line 3 is incorrect. A suggested revision is “Mesophilic C. botulinum does not grow below 10°C, and is therefore not considered a risk in VP/MAP chilled foods properly stored at <=8°C. However, both…..”

Figure 1. Determination of the safety of chilled VP/MAP foods: The 3-Step Principle

The phrase “a combination of heat and preservative factors which has been shown to consistently prevent growth and toxin production by psychrotrophic C. botulinum” at the bottom of Figure 1 fails to specify a quantitative reduction in risk, and is of no benefit to the users of this document. It is essential that a quantitative safety factor be specified. A protection factor of 6 against survival and growth from spores of psychrotrophic C. botulinum has been specified for this group of products, and is provided by a heat treatment at 90ºC for 10 min combined with maintenance at <=8ºC for up to 40 days. The same protection factor must be provided by other combinations of factors. For example, the current phrasing would permit the use of combinations of factors that consistently prevent growth and toxin production from just ten spores. Indeed the current phrasing renders the comments in the previous section of this draft document on heat treatment redundant. To bring this section in line with the section on heat treatment and to provide a quantitative reduction in risk, the phrase should be altered to read “a combination of heat and preservative factors that provides a protection factor of 6 (6 log reduction) against the risk of survival and growth from spores of psychrotrophic C. botulinum throughout the shelf-life of the product at <=8°C.” This change should be applied throughout the document.

When to challenge test

A new final paragraph should be added to “When to challenge test”. It covers an area currently lacking in this draft. “If a shelf-life of >5-10 days at >5-8°C is desired (for example 10 days at 8°C), then the specific controlling factors will need to be demonstrated, and challenge test studies should be carried out”.

In order to reflect more recent information, changes should be made to the final two sentences. It should read “Predictive models can be used as a guide to the need for challenge testing. The following packages are freely available, Growth Predictor (www.ifr.ac.uk/Safety/GrowthPredictor/default.html), Pathogen Modeling Program (www.arserrc.gov/mfs/PMP6_Start.htm), and ComBase (www.combase.cc).”

Annex: Heat treatment

The explanation of the term “protection factor of 6” (as given in brackets) in the heat treatment section in the annex is incorrect. The current text in brackets explains the meaning of the term D-value. D-values are determined with recovery at optimum temperature. A heat treatment of 90°C for 10 minutes (or equivalents) followed by recovery at <=8°C and a shelf-life of 40 days gives a “protection factor of 6”, but if recovery is at optimum temperature or is over a longer time period, this protection factor is not achieved. The piece in brackets should be “(The protection factor is the number of decimal reductions in the probability of survival and growth of the organism in the product. It combines the effect of heat treatment and of inhibitory factors. A heat treatment at 90ºC for 10 mins combined with subsequent maintenance at =8ºC for up to 40 days provides a protection factor of 6, i.e. this combination reduces the probability of survival and growth from spores of C. botulinum by a factor of 106, a 6 log reduction. The same heat treatment combined with maintenance at higher temperatures gives a lower protection factor)”.

The phrase “For long shelf-life foods (>40 days) stored at chill temperatures <=8°C, research published since publication of the ACMSF advice and Industry Code of Practice suggests that in addition to a heat treatment at 90°C for 10 minutes (or equivalent), challenge testing may be needed to establish the maximum shelf-life” that appears as footnote 5 on the first page of the annex does not give clear direction to the user. How is “challenge testing may be needed to establish the maximum shelf-life” to be interpreted? It is suggested that this phrase is replaced with “challenge testing should be carried out to establish the maximum shelf-life”. Furthermore this point is very important, and must also appear in Figures 1 and 2.

Annex: Salt content

The phrase currently in footnote 8 on annex page 2 should also provide the user with clear direction. This should be revised to “For long shelf-life foods (>40 days) stored at chill temperatures <=8°C, research published since publication of the ACMSF advice and Industry Code of Practice suggests that higher sodium chloride levels may be required to inhibit psychrotrophic C. botulinum, and challenge testing should be carried out to establish the maximum shelf-life”. Furthermore this point is very important, and must also appear in Figures 1 and 2.

Annex: Combinations of factors

The final section on combinations of factors should be revised to reflect comments made about delivering a protection factor of 6. The section in italics should be revised to “NB: These specific combinations need to be established using sound scientific principles; this is a highly specialised field and expert advice is needed. Mathematical models (e.g. Growth Predictor, Pathogen Modeling Program) can be used to obtain relevant information on combinations of controlling factors, but it is necessary to demonstrate by challenge testing, that the preservation system chosen can deliver a protection factor of 6 against the risk of survival and growth from spores of psychrotrophic C. botulinum throughout the shelf-life of the product <=8°C.”

Table 1

It is very difficult to see how Table 1 contributes to the implementation of the ACMSF recommendations/Code. Since the purpose of this document is to provide simple and easy to use guidance on the control of C. botulinum, the inclusion of this table is surprising since the ACMSF recommendations/Code do not deal with most of the organisms in the table. In order to promote ease of use, deletion of Table 1 should be very strongly considered. (However, if it is decided to retain Table 1, thought should be given to who would use this table, and how they would use it. Is it intended that Table 1 be used to assess concerns with regard to other foodborne pathogens? (For example, from this Table, B. cereus would appear to be a serious concern). If so there is probably a need to state this explicitly, and to provide more advice on how this might be achieved practically. Also, please note that 90°C/10 min does NOT, in itself, deliver a 6 log reduction for psychrotrophic C. botulinum (see other comments in this response), and in the column headed “minimum a_w for growth”, it should be made clear that the minimum value allowing growth depends on the humectant. In the case of mesophilic and psychrotrophic C. botulinum, the figures given, 0.97 and 0.94, relate to the control of water activity by NaCl. If water activity is not controlled by NaCl, but by other components of the food, growth of mesophilic and psychrotrophic C. botulinum may occur at lower values of a_w. The information given for the other bacteria also needs to be checked; if it all relates to water activity controlled by NaCl then the column should be headed “Minimum a_w for growth (a_w controlled by NaCl)” and a footnote should state “if a_w is controlled by other factors, growth may occur at lower a_w”. A further question is what is the meaning of “f” in the water activity column for S. aureus).

Other comments

The introduction should start by stating that the guidance is based on ACMSF advice (1992, 1995) and subsequent research. [Please note above comment that the current document is not consistent with the code].

Lines 13-14 of the introduction. Please note that C. botulinum is considered an obligate anaerobe. It is also unclear what the phrase “more at risk” means. VP/MAP are more at risk than what? Please consider revising to “As this bacterium grows in the absence of air, VP/MAP products are a risk”.

There would be merit in clarifying the meaning of the term “shelf-life” particularly with regard to the issue of pre-distribution storage at <3°C. The following could be added to Figure 1 “In this document, shelf-life is defined as either: (1) the time from date of production until the “use-by” date, or (2) if the product is maintained at <3.0°C from the date of production to the date of distribution, then the shelf-life is from the date of distribution until the “use-by” date”.

In Figure 1 (and elsewhere). The first category in step 2, should be “Safety with respect to C. botulinum is dependent on storage at <=5°C for up to 10 days”. Products have a specific requirement determined by shelf-life and storage temperature. The same point applies to the second category in step 2. The phrase should be “Safety with respect to C. botulinum is dependent on storage at <=8°C for up to 5 days”.

Consideration should be given to omitting Figure 2, because it is mainly a duplication of information in Figure 1, and thus may confuse the issue. If Figure 2 is retained, then “storage at <=8°C” should be added to the long shelf-life section (since temperature is defined elsewhere in this Figure).

To avoid confusion, the term “salt” should be replaced, or followed by, “sodium chloride” throughout.

The water activity of 0.97 mentioned in Figure 1 and elsewhere relates to when sodium chloride is the controlling factor. Lower water activities may be required if other factors are controlling water activity (for example in chilled pasta). Throughout the document, this should be revised to “an a_w of 0.97 (controlled by sodium chloride) or lower throughout the food”.

In the section “When to Challenge Test”, the final sentence in bold should be revised to “then the shelf-life of the food should be reduced to <=10 days at 3-5°C, or <=5 days at >5-8°C (or the specific control factors detailed in Figure 1 implemented).

Lines 1-4 in the section on “Background information on the specific controlling factors” should be revised. This is proposed since it is unclear why Listeria monocytogenes is introduced into the document, and it is very difficult to understand what specific steps could be used to remove spores of C. botulinum. To aid clarity the following revision is suggested “In an unpreserved VP/MAP food stored at <=8°C, growth of C. botulinum will be slow. Since spores of C. botulinum are ubiquitous in the environment, it is assumed that the food is liable to be contaminated. It is on this basis…..”.

The footnotes contain a substantial number of errors, and require editorial attention. For example, references 1 and 5 are the same, the wrong reference is cited on several occasions, and there are two different footnotes numbered 5, but not one numbered 7.