Demonstrating control of Listeria in food

Gail Betts, Microbiology Group Manager

A challenge for food business operators when showing effective control of Listeria in ready-to-eat foods is the uncertainty of whether their evidence to control this pathogen will be accepted by the competent authorities. In this video, microbiologist Gail Betts discusses how her new member-funded research project will tackle this issue.

About Gail Betts

Dr Gail Betts has worked at Campden BRI for over 40 years. She started working in our Thermal Microbiology group in 1984 and was part of the research team that produced the data on the heat resistance of Listeria monocytogenes and Clostridium botulinum that forms the basis of industry accepted heat processes of 70°C for 2 minutes or 90°C/10minutes aimed at producing safe chilled food products. Gail then moved on to manage the Processing, Preservation and Spoilage section within the Microbiology department where she studied predictive food microbiology, the growth and survival of spoilage organisms and food pathogens and use of traditional and novel food preservation systems. She did her industrial PhD at Surrey University during this time on the predictive microbiology of meat products.

Gail has written many guidance documents on shelf-life protocols and challenge testing and has been a member of the European Working group that produced the technical guidance document for conducting shelf-life studies on Listeria monocytogenes in ready-to-eat foods. She was also part of the ISO working group that produced the international standard on challenge testing. Gail is a member of the MicroVal Technical Committee which is responsible for validation of alternative microbiological test methods and regularly attends meetings of the Advisory Committee on the Microbiological Safety of Foods as an invited member of the public.

Gail became the Head of Microbiology at Campden BRI in July 2021 and now manages over 50 experts and technical staff focussing on molecular microbiology and methods, emerging microbiology and viruses, microbiological safety and spoilage, industrial process microbiology, brewing microbiology and microbial risk assessment.

Working at Campden BRI has given Gail insights into many areas of the food, drink and allied industries. She has helped many companies to develop new products, evaluate new processing options, optimise packaging solutions and ensure the safety of chilled, ambient and frozen food products. She is still as passionate as ever about translating scientific knowledge into practical solutions for the food industry within the UK and globally.

Read more...


All food business operators must show that their ready-to-eat foods are safe in terms of Listeria monocytogenes. It's really important that they do this because it's a legal obligation and in European microbiological criteria legislation. There's a particular regulation number 2073/2005 which has limits for different categories of ready-to-eat foods so all food business operators must show compliance with that regulation.

The challenge that arises when you're trying to show effective control of Listeria ready-to-eat foods is that you're not sure exactly what type of evidence is going to be acceptable to either your customers or to the competent authorities and there's some examples in the media of how food business operators have recently failed to do this. There have been incidences of Listeria outbreaks through foods or there have been cases where ready-to-eat food products have had to be recalled because the food business operators have not been able to show that they've got effective control of this organism in those food products.

There are a number different types of evidence that food business operators can gather. The first of these is challenge testing this is where you take a food product and deliberately inoculate it with Listeria and you store it over its normal storage conditions and see if it grows in the product during its life. Another method you can use is predictive modelling this is where you're using a mathematical model to effectively predict a likelihood of Listeria growing in the food product and you do this based on the properties of the food such as its pH and water activity. Another one durability studies and again you're looking for the growth of Listeria in the food project but this time you're not inoculating it, you're just hoping that you can find a naturally contaminated batch and therefore you see what would happen to the levels of Listeria in that food product if it ever happened to become contaminated. Finally there's what we call historical evidence. So all food business operators will gather information on the likelihood of finding Listeria when their food factories or in their products and if you collect all that data together then it will show the competent authorities the likelihood of their food from being contaminated in the first place with this organism.

The problem with looking for evidence for Listeria controllers is that are the reason to general consensus across the whole of the food industry, so competent authorities on customers might give more credence to one piece of evidence than another. So what we're really hoping to do is to get a broad approach that everyone can buy into, so everyone views the different types of evidence in the same way.

We're just about to start a new research project at Campden BRI which is looking into the whole issue of effective control of Listeria ready-to-eat in foods. So I'm quite excited to have the opportunity to work with industry and we're going to gather a group of experts together which represent manufacturers retailers scientific experts and competent authorities to sit down and look at some evidence that we're going to gather from case studies. We're going to go into two or three different factory environments produce some different types of food and I'm going to gather evidence from the different approaches that I've mentioned before. We're going to do some challenge tests on the foods we're going to look at historical evidence durability studies if we can find some naturally contaminated batches and some predictive model modeling and then we'll get their group together and I'll look at the impact of the different sources of evidence. Hopefully you'll be able to assign scores to these so that anyone wanting to see if they've got control of Listeria in their factories know that if they get a score of 15 then they're safe, if they get a score of maybe five then there isn't enough evidence to show that they have Listeria under control.

More on NPD and reformulation

People preparing food in a kitchen with sensory booths attached

Tools for streamlined and successful product development

Two solutions to help your product development effectively and efficiently keep pace with market demand – facilitating a complete understanding of your produ...

Range of high fat, salt and sugar foods

Promotional restrictions in the UK for products that are high in fat, sugar and salt (HFSS)

An open consultation for England was opened in December 2022 on the introduction of secondary HFSS legislation for the further advertising restrictions on TV...

Sensory panel tasting food

Track the quality of your products using benchmarking

Benchmarking is an excellent, cost-effective way to get an ‘informed consumer’ perspective on your products, without the need to pay for input from real cons...

Young woman eating chocolate

The power of using time-based sensory mapping with consumers to characterise your product

The power of sensory data from consumers. A guide to the key outputs of conducting time-based sensory mapping with consumers , the valuable applications of t...

Sensory panel analysing biscuit product

Leveraging sensory insights throughout the product lifecycle

Explore the benefits of applying sensory analysis to produce robust sensory data and make more informed commercial decisions, as well as the risks of not inc...

Woman biting a small chocolate

The benefits of applying consumer insights

Whether developing a new product, optimising an existing one, or looking to leverage insights into consumer journeys, we can help you produce winning product...

Contact an expert