What Factors Are Required for Microbes to Grow, Survive, and Die?

Abstract

This chapter focuses on the impact of extrinsic and intrinsic factors that impact the growth of bacteria and fungi in foods. A bacterium with a generation time of 20 min can grow from 1 cell to over a million in 7 h. Intrinsic factors that impact microbial growth or survival are those properties within the food itself. Examples of such factors are the amount of available (not chemically bound) water (i.e., water activity), the oxidation/reduction potential (ORP) of the food, its pH, and the type of acid present. Extrinsic factors are those applied to the food such as thermal processes and refrigeration. Sometimes extrinsic factors such as heating result in creation of intrinsic factors such as a reduced ORP. The dynamic interaction between intrinsic and extrinsic factors will have a profound effect on the type of microbiota in the ingredient, food, and factory environment. The extrinsic and intrinsic factors that impact microbial survival and growth in food or in factory niches are manifold and can be quite dynamic. This highlights the need for research to better understand the relationship of microbes to their environments. Food processors should exercise appropriate caution (e.g., via challenge studies, appropriate testing, selection, and monitoring of valid CCPs) when formulating new products. Assumptions about microbial behavior in one product may not necessarily apply to another.