EFFECT OF MODEL PARAMETER VARIABILITY ON THE UNCERTAINTY OF REFRIGERATED MICROBIAL SHELF-LIFE ESTIMATES

Monte Carlo procedures can be used to evaluate the uncertainty of food safety and quality estimations caused by the variability in model parameters. This study describes shelf-life predictions based on the growth of Lactobacillus sakei in meat using Ratkowsky-type models, considering the effect of temperature, water activity (A(w)) and modified atmosphere. The shelf life predicted when parameter variability was not considered was 7.0 h for a temperature-only model (Case 1, T = 4C), 184.6 h for a temperature and Aw model (Case 2, T = 4C, Aw = 0.98), 6.4 h for a temperature and CO2 model (Case 3, T = 4C, CO2 = 2,650 ppm) and 241.6 h for a temperature, Aw and CO2 model (Case 4.1, T = 4C, Aw = 0.98, CO2 = 2,650 ppm), whereas 7.4 +/- 3.5, 190.4 +/- 34.8, 7.5 +/- 2.0 and 266.1 +/- 65.8 h, respectively, were the values estimated considering parameter variability. Examining the frequency distribution of the predicted shelf life, as well as imposing a 95% confidence that meat will not spoil before its expiration date, leads to a recommended shelf life of 4, 141, 6 and 176 h for Cases 14.1, respectively. If the standard deviation (SD) of all model parameters in Case 4.1 could be lowered by 10, 50 and 90%, the recommended shelf-life time would increase from 176 to 189, 198 and 202 h, respectively (Case 4.6). The analysis of the impact of lowering the individual SD of the model parameters (Cases 4.24.5) showed an even lower impact. This suggests that lowering the uncertainty of microbial shelf-life predictions is very difficult when multiple factors are considered in the microbial model used for this estimation.