Predicting the reduction in microbes on the surface of foods during surface pasteurisation—the ‘BUGDEATH’ project

Abstract

The prime objective of the BUGDEATH project was to produce accurate predictive models of the reductions in microbial numbers that can be achieved on the surface of foods during surface pasteurisation processes. These models will enable a wide range of food manufacturers to design more effective and efficient surface pasteurisation treatments than can be produced with current microbial death models and data. During the project test apparatus was built and delivered to partners that can create ‘rapid’ heating processes, where surface temperatures rise from 5 to 100 °C in less than 1 min, can be held at a set temperature and then cooled rapidly. Slower heating and cooling processes can be carried out to compare the effects of heating and cooling times on bacterial death. Both dry and wet (steam) heating were possible. The partners carrying out microbiological trials used the test apparatus. Bacterial death was monitored by viable counts and also by specialist techniques including use of a low light-level camera and bacteria tagged with lux genes. Using organisms which have been treated by adding lux genes to make them glow (bioluminescence), and applying them to the food surface to be treated, the scientists can quickly measure changes taking place in the bacteria. If the bioluminescence fades when the food is treated then the process is effective. The bacteria glow brightly when healthy, fade when expiring and stop glowing the moment they stop metabolizing. The major aim of the project was to create a user-friendly heat transfer and microbial death model. These models were validated against published data and data provided by the partners. The programme simulates inactivation kinetics of microorganisms on food surfaces, during dry and wet pasteurisation treatments under constant and time-varying temperature conditions. On the basis of selection of a heating regime of the medium, the programme allows accurate prediction of food surface temperature and simulates the microbial load content along the whole process time. Input data and simulated values can be visualised in graphics or data tables. Printing, exporting and saving file options are available. It includes a useful database of foods (i.e. beef and potato) and related thermal properties, microorganisms (i.e. Listeria monocytogenes and Salmonella) and corresponding inactivation kinetic parameters. The software can be used to simulate results during pasteurisation treatments. The pull off simulations can be valuable to a wide variety of companies in the food industry for developing appropriate and safe processes. The software has also the potential of being exploited for educational purposes. The project involved 8 partners from 5 countries and was coordinated by FRPERC from the University of Bristol, UK. As part of the project the research team recruited an Industrial Advisory Group (IAG) to ensure that the project was relevant and useful to the European food industry.