Discovering why some foods spoil and how bacteria survive heat treatments designed to preserve our produce has got one step closer Being able to identify contaminants accurately, and early on, could allow us to buy crunchier vegetables and less highly processed food in the future according to the researchers.
Food microbiology is at the heart of improvements in both the quality and safety of our food today. However, it has become apparent in recent years that novel approaches are needed if further improvements in food microbiology are to be achieved.
This is evident in preservation processes in which a preservation treatment such as heat is applied, but whose effect can only be measured indirectly after a few days by counting numbers of surviving cells in a classical ablack box' approach.
The direct effect of this treatment on target organisms, however, remains unclear and in many cases the result can be over-treatment of food with a subsequent waste of energy and reduction in food quality. By taking a novel approach to opening this black box, Dutch scientists are hoping to make major improvements in food microbiology.
The genomic response
A cell can be seen as a highly organised collection of biomolecules including DNA, RNA, proteins, sugars, metabolites and minerals. An alteration in environmental conditions, for example a rise in temperature, will prompt a cascade of biological reactions (transcription, protein synthesis, metabolic changes and more) specific to that alteration. By measuring all the changes in all the biomolecules, the particular condition (in this case, the temperature) can be accurately described.
This measurement has only recently become technically feasible with the latest developments in genomics technologies now enabling scientists to perform these genome-wide measurements of biomolecular changes. Put simply, genomics measures changes in all RNA transcripts (transcriptomics), proteins (proteomics) or metabolites (metabolomics).
The new scientific approach has been developed to fully exploit the power of these novel technologies. The reductionist approach that had governed most research in the area of life sciences for the past decades has the drawback of causing the scientist, prior to performing an experiment, to focus on a single detail, based on a agut feeling hypothesis'. The novel genomics technologies, on the other hand, make use of a holistic unbiased approach in which the whole set of biomolecules is studied under specific experimental conditions. The application of bioinformatics, for example pattern recognition, will result in a proper characterisation of the genomic response of the micro-organism relevant for the condition under study.
Known as applied microbial genomics (AMG), this new approach directly measures to total response of the spoilage microorganism's biomolecules to the preservation methods applied.
In a food science initiative supported by the Dutch government, scientists from the University of Amsterdam looked at the way the Bacillus group of bacteria can produce exceptionally heat resistant spores. These spores can survive the processes meant to kill them, like pasteurisation, and go on to grow, multiply and contaminate our food
"We are using molecular techniques to uncover the heat resistance secrets of these spores, and to find out how they survive the preservation processes,“ said Bart Keijser from the University of Amsterdam. ""Once we have identified their unique genetic fingerprint, we can design new detection systems to find any micro-organisms that have survived heat treatment. This will give the food industry the chance to adjust their food production and preservation processes.“
Until now the food industry has had to assume that in every case, the worst possible type of contamination has already happened, leading to over-processing of most foods. Using the scientists' results, companies will be able to pre-screen ingredients, use the best preservation method in each case, and reduce energy costs and losses from contamination while maintaining safety levels.
"I hope this will mean we need less preservation techniques, and so less processing for most food. That should give us enhanced food structure such as crispier vegetables, while still maintaining a long shelf time,“ added Keijser.
Research work has already identified more heat resistance from the bacteria when some food ingredients such as milk powder and spices are used. The amount of minerals the spores can absorb also seems to contribute to their heat resistance.
A key advantage of AMG is that all the relevant responses can be measured in one experiment. To this end, Dutch scientists have developed mRNA micro-arrays with thousands of genes of micro-organisms of our food spoilage micro-organism database. This will result in a robust micro-array for applied research, enabling them to predict the outcome of a preservation treatment and to define additional preservation steps if necessary. Their experience in food microbiology, including knowledge and collection of food spoilage organisms, skills for extraction of microbial DNA and RNA of food product samples and the input of the large data-analysis group appear to be crucial in this type of applied microbial genomics research.
As an example, to measure changes in RNA molecules (transcriptomics) induced by heat treatment, target micro-organisms were grown in a food matrix and subjected to various heat treatments. RNA molecules of micro-organisms subjected to the various treatments were isolated and used for transcriptomics analysis. Expression patterns of various conditions were generated and analysed by principal component analysis. The effects of different temperatures on growth can be clearly distinguished on the basis of this analysis. So this approach can be used for a rapid analysis of efficacy of a heat treatment on target organisms in food.
In addition, the application of AMG is not limited to preservation technologies. In principle, all processes which involve living micro-organisms are amenable to the concept. A number of applications are currently being developed with industrial partners. These include: quality control systems for fermented foods; development of an integrated system for tailor-made process control for processed food; development of microbial detection systems for the quality control of raw materials; identification of novel antimicrobial compounds; and development of novel diagnostic systems for pathogens.
