Estimation of the survival curve of Listeria monocytogenes during non-isothermal heat treatments

Published survival curves of Listeria monocytogenes under several constant temperatures in the range of 50-65 degreesC could be described by the model Log(10)[S(t)] = -b(T)t(n(T)), where S(t) is the momentary survival ratio, and b(T) and n(T) coefficients whose temperature dependence was expressed b y empirical models. When the temperature history T(t) is also expressed alg ebraically, b(T) and n(T) are transformed into time dependent terms, b[T(t) ] and n[T(t)] respectively. If there is no growth and damage repair during the heating process, and the momentary inactivation rate only depends on th e momentary temperature and survival ratio, then the solution of the differ ential equation dLog(10)[S(t)]/dt = -b[T(t)] * n[T(t)] * {- Log(10)[S(t)]/b [ T(t)]} <^> (n[T(t)] - 1)/n[T(t)] provides the survival curve under the sp ecified non-isothermal conditions. The validity of this model is demonstrat ed by the agreement of its predictions, calculated numerically using Mathem atica (R), to reported survival data of Listeria during heating at a consta nt and varying rates. Unlike in the traditional calculation methods of micr obial survival, the one employed here does not require that microbial morta lity be a process following a first or any other order kinetics model. (C) 2001 Elsevier Science Ltd. All rights reserved.