New model predicts listeria growth

The project has run over several years and is supported by the Danish Ministry of Food and Agriculture through the so called GUDP funds (Green Development and Demonstration Program).  Ole Mejlholm, Senior Researcher at the division of Industrial Food Research at Technical University of Denmark (DTU), led the project in cooperation with Niels Bøknæs, Process Developer at Royal Greenland and Industrial Ph.D.. Royal Greenland supplied samples from the production of cold smoked Greenland halibut and salmon and the researchers at DTU worked with these in the lab, developing the mathematical model predicting the development of listeria, including the effects of 12 environmental factors such as storage temperature, pH, salt content, smoke content and processing procedures. Subsequently, Royal Greenland tested the model and implemented the findings from the project in the daily operations in the smokehouse.

Food safety and listeria are to be taken seriously and for that reason the model has been tested thoroughly. Senior Researcher Ole Mejlholm states: "It has taken several years to develop the mathematical model for Listeria monocytogenes. Actually, we began to develop it in collaboration with Royal Greenland more than 12 years ago and today we have a successful model, which the Danish Veterinary and Food Admonistration last year recommended to all companies working with this type of products and food safety."

Simplified development process

To Royal Greenland, the development of the mathmatical model has meant a significantly simplified product development process. Niels Bøknæs says about the model: "This new tool is brilliant. With the model we can save both time and money when developing new products. Before we had to do lengthy trials if we wanted to, for example, lower the salt content of a product. Now, all we have to do is start up the computer and enter the new data in the software and at the push of a button, we get a clear idea of what the new values will mean for the safety of the product and how it will affect the growth of bacteria during the product lifetime. It simply shortens our development process in these challenging semi-preserved products."

Stabilization of listeria growth

Not only has the research project allowed Royal Greenland to predict how listeria and other bacteria develops under a number of different environmental factors, but, it also showed that lowering the pH value of a product with organic acids, meant that listeria was not able to grow. This was a very important discovery as listeria can grow under conditions where other bacteria are not able to, e.g. at refrigerator temperature and in the absence of oxygen.

Mejlholm explains: "It is possible to use organic acids such as lactic acid and acetic acid to control bacterial growth, but we are also examining certain spices or spice extracts and the possibility of adding other harmless bacteria cultures inhibiting the growth of the dangerous ones". Royal Greenland has implemented this in their production of cold smoked and marinated fish, adding a mixture of harmless organic acids, which do not affect the taste of the final product, in the salting process, resulting in a product in which listeria is not able to grow. Read more here It is important to note though, that stabilization cannot stand alone, but needs to be complemented by thorough cleaning routines and control of raw material supply – read more here.

Lowering salt levels

In the past, the procedure in the industry has been to add a lot of salt in order to be on the safe side when it comes to bacterial growth and shelf life, as the content of salt has a growth inhibiting effect on many bacteria. With the mathematical model it is possible to predict what will happen when salt levels are lowered. Bøknæs states: "The goal for our first GUDD project with DTU was to lower the salt content by 4% per year in our cold smoked and marinated ranges and we have reached that goal. But, we want to go as low as we possibly can, while still ensuring safe and tasty products. No one really knows how low we can go, but we will continue to challenge this in collaboration with DTU". The reduction in salt content is important from a health perspective and today about 80% of the salt consumed comes from processed foods. Bøknæs explains: "We are experiencing an increasing demand for products with lower salt content from our customers, especially from the UK and Scandinavia, and from consumers in general, and we want to be the frontrunner in the industry in this field."

The future

The software based on the model is available online for anyone to use and today, the program has more than 6000 users from 100 different countries, who continuously reviews it. The credibility and independence of the model is guaranteed by DTU.  Originally the program was developed for the seafood sector, but it is also now verified for use in the meat and dairy industries. Bøknæs concludes: "We are happy that other actors in the industry can use the software and hope that this will help put food safety on the agenda in the industry, considering the recent outbreak of listeriosis in Denmark. We have a common responsibility to do so. Also, we hope that food safety will be put on the agenda as a demand to suppliers from both retail and food service businesses."