Application of a complete heat-water model to predict microbial growth and inactivation during airflow treatments at the surface of meat products
Résumé
A previously developed water transfer model was combined to a microbial model to predict the growth of Listeria innocua CLIP 20595 during storage and slow drying of meat products. The same water transfer model was coupled to a thermal model to predict the rapid evolution of surface temperature (Ts) and water activity (aw) during dry air decontamination of beef lean meat. Storage predictions were validated in a wind tunnel where bacterial growth was measured at the surface of gelatin gels for several days under constant air temperature and 3 different controlled air velocity and relative humidity conditions. The predictions of Ts and aw during decontamination treatments were validated in a rig where the surface temperature was measured by a calibrated infrared sensor under controlled air conditions. Water activity was determined from sample weight losses measured at different time intervals during the treatment. Wind tunnel experiments showed that L. innocua growth was stopped at a relative humidity of 92.5% and a velocity of 4.6 m/s. The maximum population did not exceed 5 log10(CFU/cm2). The different behaviours of L. innocua under the 3 drying conditions were accurately predicted by the combined water transfer/growth models. For the surface decontamination treatment, comparison with measurements proved that the coupled heat-water model was able to accurately calculate temperature and water activity at the surface of a meat sample even under rapidly changing conditions. The surface temperature and aw calculated by the transfer model were used in an inactivation model to predict microbial decontamination of S. typhimurium based on parameters estimated in the literature.