The detection and characterisation of microbial contaminants in raw materials, intermediate and end products is important for improving product quality and process efficiency. The project has addressed research needs that include concentration methods for the detection of extremely low numbers of microorganisms (Concentration subproject), insight into the composition and outgrowth of the microbial spoilage population (Composition subproject), and insight into the physiological state of spoilage microorganisms in order to reduce their survival in food processing and preservation conditions (Physiological state subproject).
In the Concentration subproject we have developed milk pretreatment 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 subproject 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 compared 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 subproject, 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.