The detection and characterisation of microbial contaminants in raw materials, intermediate and end products is important for improving product quality and process efficiency. The Detection project has addressed research needs that include concentration methods for the detection of extremely low numbers of microorganisms (Concentration), insight into the composition and outgrowth of the microbial spoilage population (Composition) and insight into the physiological state of spoilage microorganisms in order to reduce their survival in food processing and preservation conditions (Physiological state).
In the Concentration sub-project we developed milk pre-treatment methods based on proteolytic digestion. These methods have allowed the entrapment and enumeration of microorganisms on a microsieve. Experiments for the detection of spores in clear media by the microsieve method showed a detection limit of approximately 103 spores per ml. In the Composition sub-project we applied mass sequencing to monitor the spoilage population in a ready-to-eat rice meal, during spontaneous spoilage in the absence or presence of weak organic acids, in order to assess the effects of these acids on outgrowth and compare the results to those obtained by conventional plate counting. In addition, we monitored the presence and outgrowth of a mixture of bacterial spores in a soup matrix using a very similar approach. In the Physiological state sub-project, analysis of heterogeneity in the heat-stress-resistance of Bacillus subtilis was carried out using live/dead stains followed by single-cell analysis. The differences observed in stress sensitivity appeared subtle.
The project was successfully completed in 2013 and has resulted in a paper in the peer-reviewed journal Applied Environmental Microbiology (Yu et al), and a cross-project collaboration with Biofilm and Detection – another project within the theme Food Safety and Preservation. The project also delivered a manuscript with active input from the two industry partners involved in the project. Moreover, the outcomes were received with interest at the SPOILERS 2013 congress in Quimper (France). A review on cultivation-independent detection of extremely low amounts of micro-organisms is under preparation, initiated by Wageningen UR Food & Biobased Research – one of the research partners in the project.