By Linda Everis - 15 February 2019

From a technical perspective, product shelf-life is the time after production that a product remains safe and retains the desirable attributes of product quality with respect to chemical, sensory and microbiological characteristics. It needs to be free from food borne pathogens and maintain an acceptable level of spoilage organisms. It is illegal to sell food which has deteriorated during storage so as to be injurious to health, or if its quality has deteriorated beyond that which would normally be acceptable.

Assigning the correct shelf-life requires a great deal of thought. Obviously, if it is too long there is the potential for food spoilage or growth of food pathogens - and the product will not meet the requirements of food safety legislation, but if it is too short (i.e. over cautious) then manufacturing costs and wastage may increase, and profit margins drop. Consequently, it is important to assign the shelf-life in a systematic and scientific manner, taking all relevant factors into consideration. It’s also important to re-evaluate shelf-life when products are reformulated – even minor changes in product formulation can have a substantial impact on the growth of micro-organisms. Changing or reducing levels of a preservative, or reducing the salt, sugar or fat levels or types can all impact on shelf-life.

Factors affecting shelf-life

Manufacturing, product formulation and storage conditions all have an influence on shelf-life, so the effect of these on the growth of target microorganisms must be considered.

The food business operator should have enough product knowledge to be able to determine which factors will limit its shelf-life, and the approximate time for which the product will remain fit for consumption (i.e. days, months or years). This could be by comparison with similar products with a clear insight into the differences between these 'similar' products and the product in question.

When microbiological issues are important, there are three basic approaches that are used to assess product shelf-life:

• shelf-life trials
• challenge tests, and
• predictive microbiology

Each has a key role to play in assuring the safety of the product shelf-life chosen.

Shelf-life trials

How long does this product remain within the designated quality parameters during normal production and storage conditions?

That’s the question that shelf-life trials are designed to answer. These tests assess only the growth of naturally present micro-organisms in the product batch being tested. These trials do not determine the potential for growth of foodborne pathogens because it is unlikely that pathogens would be present in the product.

The shelf-life of food products is determined in a logical sequence of events:

• Kitchen/pilot scale assessment: the product and process characteristics are defined and a target shelf-life decided.
• Factory scale trials: the majority of laboratory testing is performed on batches of product produced under routine manufacturing conditions and where the shelf-life of the product isassigned. During this stage, the product is stored under conditions to which it is likely to be exposed during retail distribution and examined for any changes in levels of target micro-organisms.
• Full scale production: any changes to the shelf-life are monitored.

It’s important to note that the shelf-life determined in these studies is only relevant to the product formulation and storage conditions used and cannot be extrapolated to other conditions.

Challenge testing

Will the product formulation and storage conditions control growth of pathogens (or spoilage organisms) during the designated shelf-life if they were present in the ingredients or contaminated the food during manufacture?

Challenge testing answers this question.

With challenge testing, a food is deliberately inoculated with the relevant organisms and the growth of the organism is studied under controlled laboratory conditions. The advantage of this technique is that it provides data to answer the ‘What if?’ questions that may not be answered during shelf-life studies, e.g.

• What would happen if Listeria monocytogenes contaminated my product after cooking?
• What would happen if a preservative resistant yeast survived the processing?

Predictive microbiology

Predictive microbiology uses computer simulations to predict the likely growth of spoilage organisms or food pathogens in different product formulations or storage conditions. It provides a rapid answer for use in new product development and troubleshooting situations. Data can be obtained on the length of lag time, rate of growth and the time taken to reach a target number of organisms. In addition, many models can be used to predict the effect of fluctuating temperature profiles that may be seen during shelf-life.

A more comprehensive description of predictive microbiology (PDF).

Conclusion

The shelf-life of food products is influenced by microbiological, chemical and sensory considerations and, in some cases, legislative requirements. It needs to be determined by applying sound scientific principles that can take into account all the relevant formulation, manufacturing, distribution and storage factors.

Shelf-life is unique to the product and storage conditions tested and cannot be extrapolated to other products or storage conditions. Assigning the correct shelf-life can be the key to the commercial success of a new product and should be carried out in the early stages of new product development.

If you want to learn more about shelf-life testing and how to approach it, you might be interested in our Setting shelf-life: How to do it better seminar on 4th June 2019.

More information on challenge testing is available in: Betts, G.D. (2010) Challenge testing protocols for assessing the safety and quality of food and drink. Guideline No. 63.

More information on shelf-life testing is available in: Betts, G.D., Brown, H.M. and Everis, L.K. (2004) Evaluation of product shelf-life for chilled foods. Guideline No. 46.

This article first appeared in International Food and Meat Topics

Linda Everis
+44(0)1386 842063
linda.everis@campdenbri.co.uk

About Linda Everis

Linda has a wealth of knowledge, experience and expertise from her time in Microbiological Analytical Services and Microbiology Safety and Spoilage. She joined Campden BRI in 1995 as a Senior Technician in the Microbiological Analytical Services group having graduated from the University of Wales Aberystwyth with a BSc in Biology.

Alongside the expert support that Linda provides to our members and clients, Linda conducts project work and research, and has been author and co-author of articles and papers for a variety of microbiological publications and Campden BRI reports.

Linda also lectures on shelf-life, challenge testing and predictive microbiology for our many training courses and seminars.

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