ABSTRACT
Microorganisms exposed to low temperatures will enter a stationary phase. The cessation of growth does not necessarily signify the cessation of metabolic activity. As an organism can by definition grow at cool temperatures, its viability can be affected by such temperatures only if the exposure to cool temperatures results in the organism being cold shocked. The water in foods is mainly in the form of more or less complex solutions. The temperature at which water in a food starts to freeze will then be determined by the concentration of solutes in the water, with the ice fraction increasing over a range of temperatures. Inactivation by cold temperatures of microorganisms used for fermenting or raising foods can restrict commercial options in the preparation and processing of some foods or the maintenance of starter cultures. The minimum temperatures for growth of psychrotrophic organisms should ideally be determined in supercooled media.
