Characterisation of the resistance and the growth variability of Listeria monocytogenes after high hydrostatic pressure treatments

Abstract

The use of non-thermal methods for food preservation is due to consumer demands for microbiological safe products, without changes in the sensory and nutritional qualities of the product. High hydrostatic pressure (HHP) has emerged as an alternative to traditional thermal processing methods for foods.Listeria monocytogenes CECT 5672 was treated under HHPs (350, 400 and 450 MPa) for 3, 16 and 23 min. The effects of pH (5, 6 and 7) and sodium chloride concentration (0, 0.5 and 1.0) of the recovery medium were studied on L. monocytogenes. The kinetic parameters were estimated by the method described by Métris, George, and Baranyi (2006). From results obtained, histograms of the lag phase were generated and distributions were fitted. The duration of the lag phase of HHP damaged cells increased with the application of additional stresses. Histograms showed a shift to longer lag phases and an increase in variability with high stress levels in the recovery medium.Using a primary model together with Monte Carlo simulation, predictions of time to growth (100 cfu/g) of L. monocytogenes were established and they were compared with deterministic predictions. It was evidenced that deterministic predictions do not give a good indication of the probability of a certain level of growth.