Low-Temperature Food Preservation and Characteristics of Psychrotrophic Microorganisms

Abstract

The use of low temperatures to preserve foods is based on the fact that the activities of foodborne microorganisms can be slowed at temperatures above freezing and generally stopped at subfreezing temperatures. The reason is that all metabolic reactions of microorganisms are enzyme catalyzed and that the rate of enzyme-catalyzed reactions is dependent on temperature. With a rise in temperature, there is an increase in reaction rate. The temperature coefficient (Q10) may be generally defined as follows: $${Q_{10}} = \frac{{\left( {Velocity\;at\;a\;given\;tem. + {{10}^o}} \right)}} {{Velocity\;at\;T}}$$The Q10 for most biological systems is 1.5–2.5, so that for each 10°C rise in temperature within the suitable range, there is a twofold increase in the rate of reaction. For every 10°C decrease in temperature, the reverse is true. Because the basic feature of low-temperature food preservation consists of its effect on spoilage organisms, most of the discussion that follows will be devoted to the effect of low temperatures on foodborne microorganisms. It should be remembered, however, that temperature is related to relative humidity (R.H.) and that subfreezing temperatures affect R.H. as well as pH, and possibly other parameters of microbial growth as well.