Way of shelf-life

Industry is challenging the 10-day shelf-life rule, reports John Dunn

UK chilled foods are characterised by their short shelf-lives. Unlike many other countries, most chilled, ready-to-eat foods such as pizzas, sandwiches, recipe dishes, soups and salads that are made in the UK have shelf-lives as short as one to 10 days. And what bugs many UK food manufacturers is that these self-imposed short shelf-lives put them at a competitive disadvantage against imports.

In new guidelines just published by the Chilled Food Association (CFA) and the British Retail Consortium, British food manufacturers can now get clear and detailed guidance on how to accurately work out the safe shelf-life of their ready-to-eat products. This guidance is based on the implementation of European food regulation 2073/2005 of November 15 2005 on microbiological criteria for foodstuffs.

This requires manufacturers to be able to demonstrate levels of Listeria monocytogenes in ready-to-eat food are not exceeded. But the real problem with safe shelf-lives, say many UK manufacturers, is the basic assumptions behind the shelf-life guidelines that British manufacturers voluntarily stick to.

Drawn up in 1992, the guidelines say that the shelf-life of ready-to-eat foods should be limited to a maximum of 10 days unless they have undergone heat treatment at 90°C for 10 minutes. This is significantly tougher than basic pasteurisation (70°C for two minutes) and can have significant effects on taste and texture as well as processing costs.

In a move to inject some science into these 20-year old guidelines, the CFA is helping to fund a £750,000 three-year Department for Environment, Food and Rural Affairs food LINK project looking at the presence of cold-resistant (psychrotrophic) Clostridium botulinum spores in foods. In the project, which is about halfway through, the Institute of Food Research has been collecting around 1,800 food and ingredient samples from CFA members and project partner Unilever to analyse the spore counts and build a database.

From this it is hoped that the 10-day rule can be safely lengthened significantly and that a new, less-damaging heat treatment regime can be devised for foods destined to have a shelf-life beyond any new limit.

The SUSSLE project

It is known as the SUSSLE project (Sustainable Shelf-Life Extension), but its details and results are being kept confidential for five years from the date of its completion. This is to give UK ready-to-eat food producers an advantage over imports from countries where shelf-life rules are more relaxed.

"We are challenging the scientific basis of the 10-day rule," says Kaarin Goodburn, secretary general of the CFA. Although botulinum is the target of the SUSSLE project, there has never been an outbreak of botulinum poisoning in the UK in chilled foods, says Goodburn.

There have been a few cases in the US, but they were caused by food that had not been stored in a fridge. Britain's voluntary shelf-life rules may hamper the UK chilled food industry. "But until we are sure about safety, we are sticking with them," says Goodburn.

When the SUSSLE project is completed, the CFA hopes its findings will be incorporated into EU food law to ensure that shelf-lives are determined by scientific knowledge and to ensure a level playing field.

The issue is driven by two main factors. One is the pressure to avoid food waste. Supermarkets want to avoid waste by being able to keep food on their shelves a bit longer. And there is pressure from authorities to persuade consumers not to throw away safe food because it has passed its best-before date.

The other driver is the pressure from supermarkets for more rigorous testing for food-borne hazards and pathogens. As Dr Paul Gibbs, principal consultant in food safety and preservation at Leatherhead Food Research, acknowledges, thorough testing for food-borne hazards and spoilage organisms all takes time time that has to be deducted from a product's theoretical shelf-life.

The issue is complicated by the fact that the growth of bugs such as cold-resistant psychrotrophic botulinum can be safely slowed down by keeping foods at temperatures below 34°C. "But most domestic fridges don't run at 3°C or 4°C, says Gibbs. "They run at about 6°C or 8°C and many run at 10°C. psychrotrophic botulinum will grow quite happily at that. Listeria will grow nicely too."

Waste reduction

Barbara Gallani, food safety and science director at the Food and Drink Federation, says there is a big drive to reduce food waste by improving consumers' understanding of the best-before and use-by dates. "The WRAP report [Waste & Resources Action Programme Food Waste Report July 2008] made the headlines because of the very high number of products that were being thrown away daily."

This is largely due to consumers' confusion about on-pack information and what food spoilage means, says Gallani. "So there is this big drive by the Food Standards Agency, the industry and other stakeholders to clarify the difference between quality issues and safety issues. The hope is that this will reduce the food wastage in the home."

But there are other pressures affecting the safety of food products, aside from the desire to increase shelf-life and cut wastage. This is the drive to reduce salt, fats and sugars in our diet. The sodium in salt plays havoc with our blood pressure; fats make us fat; and sugar rots our teeth, as well as making us fat.

"But salt in almost all foods, except perhaps salted crisps, is primarily there as a preservative," says Gibbs at Leatherhead. "It is not just for taste. In bacon and cured hams, for instance, there is a requirement for 3.5% salt in water to inhibit the psychrotrophic strains of botulinum. You start playing about reducing sodium chloride, then there is a real risk of food poisoning from botulinum. Sugar, too, at reasonably high levels, is a preservative."

One of the results of cutting down on salt and sugar can be seen in the reduced preservative effect this is having in sauces, pickles and jams, says Gibbs. "If you look at labels of these products, it will now say 'refrigerate after opening'. The reason is that the levels of acid, salt and sugar, which are hurdles to microbial growth, have been reduced. Everyone seems to have forgotten the CIMSCEE Code," says Gibbs.

The CIMSCEE code (Comité des Industries des Mayonnaises et Sauces Condimentaires de la Communauté Économique Européenne) for the preservation of emulsion products using acetic acid was devised almost 20 years ago as a mathematical model for predicting the shelf-life of pickles and sauces.

Essentially it provides formulae to enable firms to produce an intrinsically safe and stable product in which acetic acid-tolerant micro-organisms will not grow. "It does work very well," says Gibbs." So you change and modify these traditional recipes at your peril."

So are there any alternatives that will help manufacturers reduce salt, fats and sugars and other preservatives and extend shelf-life without compromising safety or having to resort to harsh heat treatment processes? According to Gibbs, there are a number of promising techniques. The one getting the attention is the use of natural preservatives.

Natural preservatives

"Quite a lot of essential oils from fruits and plants are very good antimicrobials. But a lot of them have a very strong aroma or flavour," says Gibbs. "One that has been worked on a lot is oil from rosemary. It is a very good antioxidant and quite a good antimicrobial. But you have to use mind-bogglingly large amounts hundreds of times the sprig of rosemary you put on your Sunday roast lamb. You can deodorise them, but that puts the cost up and you lose quite a bit of the antioxidant activity."

Other promising alternatives are high- pressure processing (popular in the US, but expensive); ohmic heating where you pass an electric current directly through the food (only applicable to liquids); and radio frequency heating (like the domestic microwave but using longer wavelengths for better penetration).

The problem with most of these processing techniques is that they heat up the food, so if it has to be cooled afterwards, there is a cost involved and the heat is not easily recovered.

There is now an alternative to potassium chloride as a salt replacement. Soda-Lo, developed by Eminate in Nottingham, promises the taste of salt without the harmful consequences. Each particle of Soda-Lo is a microscopic hollow ball of salt. Ingredients supplier Naturis has recently signed an agreement to bring Soda-Lo to the market.

As Gibbs says, there are promising options out there. "But it will take quite a while to work its way through onto the supermarket shelves. But in five years time, who knows?"

KEY CONTACTS 