DYNAMICS OF HEAT DESTRUCTION OF SPORES - A NEW VIEW

Discrepancies between actual, viable spore populations and those predi cted by a classical model during heat sterilization of food and pharma ceutical products have long concerned food engineers and scientists as they pursue new sterilization techniques, including ultra-high temper ature processes. Among potential causes of those discrepancies, activa tion of dormant spores is significant, and models addressing that fact or were developed recently. This paper reviews historic and current vi ews on the biology and models of microbial spore populations during he at sterilization. Activation and inactivation of viable spores are emp hasized, with each viewed as a first-order reaction. Rate constants of those reactions may differ significantly, inactivation rates of dorma nt and activated spores may differ, and variations of all rate constan ts with temperature appear to be well described by Arrhenius equations . Model-based analyses show how categories of survivor response curves observed during isothermal heat treatments can arise from simultaneou s activation and inactivation of spores in an overall population. Effe cts of different distributions of initial subpopulations, different di stributions of rate constants, and 'heat shock' for homogenizing an in dicator population are shown. The complexity of new, multiple process models has not increased greatly, but the potential for accurate, dyna mic prediction of product safety after prescribed sterilization has. T he relevant biology is understood and accounted for more thoroughly, a nd it is anticipated that the new models will aid design and evaluatio n of new and improved sterilization processes for food and pharmaceuti cals.