Calculating Salmonella inactivation in nonisothermal heat treatments from isothermal nonlinear survival curves

Salmonella cells in two sugar-rich media were heat treated at various const ant temperatures in the range of 55 to 80 degreesC and their survival ratio s determined at various time intervals. The resulting nonlinear semilogarit hmic survival curves are described by the model log(10)S(t) = -b(T)t(n(T)) where S(t) is the momentary survival ratio N(t)/N-0, and b(T) and n(T) are coefficients whose temperature dependence is described by two empirical mat hematical models. When the temperature profile, T(t), of a nonisothermal he at treatment can also be expressed algebraically, b(T) and n(T) can be tran sformed into a function of time, i.e., b[T(t)] and n[T(t)]. If the momentar y inactivation rate primarily depends on the momentary temperature and surv ival ratio, then the survival curve under nonisothermal conditions can be c onstructed by solving a differential equation, previously suggested by Pele g and Penchina, whose coefficients are expressions that contain the corresp onding b[T(t)] and n[T(t)] terms. The applicability of the model and its un derlying assumptions was tested with a series of eight experiments in which the Salmonella cells, in the same media, were heated at various rates to s elected temperatures in the range of 65 to 80 degreesC and then cooled. In all the experiments, there was an agreement between the predicted and obser ved survival curves. This suggests that, at least in the case of Salmonella in the tested media, survival during nonisothermal inactivation can be est imated without assuming any mortality kinetics.