Theoretical comparison of a new and the traditional method to calculate Clostridium botulinum survival during thermal inactivation

When published isothermal survival data of Clostridium botulinum spores in the range 101-121 degreesC were plotted in the form of logS(t) vs t relatio nships, where S(t) is the momentary survival ratio, they were all non-linea r. They had a noticeable upward concavity, in violation of the assumption t hat sporal inactivation is a process that follows first-order reaction orde r kinetics. They could be described by the power law model logS(t)=-b(T)t(n (T)), where b(T) and n(T) are temperature-dependent coefficients of the ord er of 0.1-6 and about 0.4 respectively. These coefficients were used to con struct simulated survival curves under different heating regimes with a rec ently proposed model. The model is based on the assumption that the local s lope of the non-isothermal survival curve, or the momentary inactivation ra te, is determined solely by the momentary temperature and survival ratio, w hich in turn are functions of the population thermal history. The survival curves calculated with this model differ considerably from those produced b y the standard method based on the traditional D and Z values. The shortcom ings of the standard model are that these values depend on the number of po ints taken for the regression, and that its predicted survival ratios depen d on the selected reference temperature. The differential equation which is proposed to replace it can be solved numerically using a program such as M athematica(R). Its predictions solely depend on the observed survival patte rns under isothermal conditions and not on any preconceived kinetic model. Nevertheless, the method still needs verification with experimental non-iso thermal survival data, as has already been done with Listeria and Salmonell a cells. (C) 2001 Society of Chemical Industry.