Challenge Test Improvement: Analytical Costs and Time Optimization

Abstract

The study’s aim was to develop a quantitative risk assessment model of Listeria monocytogenes in liver chicken paté. The model was performed using the Integrated Challenge Test (Italian Journal of Food Safety, Vol. 1 N. 6 2012) with the objective to reduce the analytical cost and time. The challenge test was carried out on 3 different batches stored at 12°C and inoculated with a mix of Listeria monocytogenes strains. Lactobacillus spp. and Listeria monocytogenes plate counts were performed daily on each sample until the stationary phase was reached by both populations. The challenge test results at 12°C were input in the Combase DMfit software to determine the growth parameters of Listeria monocytogenes and lactic flora which showed mutual interaction. Then, using the Combase Predictor for Listeria monocytogenes and the FSSP (Food Spoilage and Safety Predictor) software for lactic flora, the growth parameters were extrapolated at 4°C and 8°C. The growth parameters of both populations at 4°C, 8°C and 12°C were then used to apply the model in order to predict the maximum daily concentration of Listeria monocytogenes. Model results were assessed against the results of an additional challenge test conducted with the same strain mix inoculum in 3 different batches stored for 4 days at 4°C, 4 days at 8°C and then 4 days at 12°C. The proposed model represents a reliable quantitative risk evaluation which provides realistic results with limited cost.