Critical evaluation of restrictions used to optimize sterization processing conditions

A computer program, using a finite differences method, was developed to model the heat sterilization for cylindrical packaged conduction heating foods. This program was introduced into an optimization routine to calculate optimum processing conditions, maximizing the surface or the volume average quality, using different restrictions. Depending on the pack dimensions and the heating rate of the product the least-lethality point is at the geometric center or along the radius or the vertical axis. Therefore, sterility values specified at the center and at the least-Iethality point were used as sterility criteria for calculating optimum conditions. The effect of an integrated sterility value constraint on optimal temperature was also investigated. Depending on the product thermal properties, processing conditions and target lethality the optimum temperature calculated using the sterility value at the center as restriction can overestimate the correct value by as much as 4°C.