CONSIDERATIONS FOR CALCULATING HEAT INACTIVATION PROCESSES WHEN SEMILOGARITHMIC THERMAL INACTIVATION MODELS ARE NONLINEAR

Bigelow's method is the basis of all modem thermal process calculation s. These calculations are based on the assumption that the heat inacti vation model follows first order kinetics. However as demonstrated in this paper; Bigelow's method is applicable in all cases when the heat inactivation process can be characterized by a relation of three varia bles: t{T,N} = g{T}.f{N}; where t = heat treatment time at constant te mperature T; T = temperature; and N = number of surviving micro-organi sms at time t. The function g{T} depends only on T and f{N} is another function depending only on N. As shown in this paper the (classic) em pirical kinetic equation satisfies this requirement, however several n on-linear semilogarithmic microbial heat inactivation models do not co nform to the above relationship. In dubious cases, when proper equatio ns for experimentally determined heat inactivation curves are uncertai n or unknown, a simple graphical method is proposed to assess whether these curves correspond to a g{T}.f{N} type function. (C) 1998 Elsevie r Science Limited. All rights reserved.