On the common misuse of a constant z-value for calculations of thermal inactivation of microorganisms

Abstract

An analysis clarifies the consequences of using the approximate equation, which is widely used for calculations of the sterilization value (F value etc.) and inactivation of microorganisms in heat processes for food. The first-order kinetics with a temperature dependence, which satisfies Arrhenius equation is reviewed. The accurate equation of the sterilization value, F – equally simple as the approximate – is mathematically clarified. The overestimation of the sterilization value when applying approximate calculations is demonstrated in terms of equations and graphs, which show that the overestimation is not negligible at temperatures that deviates just moderately from the reference temperature. The ultimate consequence is the risk of compromising food safety, particularly as increasing temperatures are more commonly employed in thermal processing of food, such as UHT processes. The article concludes by advocating the use of the exact equation that takes into account the temperature dependence of the z-value that is fully consistent with the Arrhenius equation. A graph and equation for the error is provided. Since safe and lasting food is fundamental in food production, this study is of major significance. The objective is that the literature generally and food industry particularly take the conclusion seriously by adopting the concluded equation.