Growth, Survival, and Death of Microbes in Foods

Abstract

Food microbiologists must understand microbiology and food systems and be able to integrate them to solve problems in complex food ecosystems. This chapter addresses this in three parts by (i) examining foods as ecosystems and discussing intrinsic and extrinsic environmental factors that control bacterial growth, (ii) explaining first-order or pseudo-first-order kinetics which govern the log phase of microbial growth and many types of lethality, and (iii) focusing on physiology and metabolism of foodborne microbes. Growth of Clostridium botulinum in foods such as potatoes and sauteed onions exposed to air has caused botulism outbreaks. Bacteria are classified as psychrophiles, psychrotrophs, mesophiles, and thermophiles according to the way in which temperature influences their growth. Additional barriers to microbial growth should be incorporated into refrigerated foods containing no other inhibitors. Food microbiology is concerned with all four phases of microbial growth. Growth curves showing the lag, exponential logarithmic or log, stationary, and death phases of a culture are normally plotted as the number of cells on a logarithmic scale or log10 cell number versus time. These plots represent the states of microbial populations rather than individual microbes. Thus, both the lag phase and stationary phase of growth represent periods when the growth rate equals the death rate to produce no net change in cell numbers. Food microbiologists frequently use doubling times (td) to describe growth rates of foodborne microbes. Developments in molecular biology and microbial ecology will change or deepen the perspective about the growth of microbes in foods.