Chapter Three - Microbial Destruction in Thermal Processing of Foods

Abstract

This chapter focuses on microbial survival data in thermal processing, where heat is applied to foods to kill microorganisms. The number of surviving microorganisms, after a selected heating duration, is determined to obtain the decimal reduction time, commonly called the “ D -value.” The chapter then goes on to calculate the effect of temperature on the rate of microbial destruction, expressed by the thermal resistance factor called the “ z -value,” which is unique for each microorganism. Experiments involving thermal resistance of bacteria are discussed. This involves determining the data on surviving microbes at different temperatures, which are analyzed to obtain the D -values. While conducting sampling for the presence or absence of microbial contamination, it is often desirable to know how many samples should be tested. Statistical analysis using binomial distribution allows the determination of the number of samples needed for such purpose. Problem statements, discussions, and worksheet comments are presented to determine the process lethality for conduction of heating food and to calculate the thermal process time for food with a microorganism. Also, center and mass-averaging sterilizing values are discussed.