Chapter 16
Protection of Foods with
Low-Temperatures, and
Characteristics of Psychrotrophic
Microorganisms
The use of low temperatures to preserve foods is based on the fact that the activities of 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 (Q 10 ) may be generally defined as follows:
Q 10 =
(Velocity at a given temp. +10
◦ C)
Velocity at T
The Q 10 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 pathogens and spoilage organisms, most of the discussion that follows will be devoted to the effect
of low temperatures on these microorganisms. It should be remembered, however, that temperature
is related to relative humidity (RH) and that subfreezing temperatures affect RH as well as pH, and
possibly other parameters of microbial growth as well.
DEFINITIONS
The term psychrophile was coined by Schmidt-Nielsen in 1902 for microorganisms that grow at
0
◦ C.
31 This term is now applied to organisms that grow over the range of subzero to 20
◦ C, with an
optimum range of 10–15
◦ C.
47 Around 1960, the term psychrotroph (psychros, cold, and trephein, to
nourish or to develop) was suggested for organisms able to grow at 5
◦ C or below.
13,50 It is now widely
accepted among food microbiologists that a psychrotroph is an organism that can grow at temperatures
395
Protection of Foods with
Low-Temperatures, and
Characteristics of Psychrotrophic
Microorganisms
The use of low temperatures to preserve foods is based on the fact that the activities of 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 (Q 10 ) may be generally defined as follows:
Q 10 =
(Velocity at a given temp. +10
◦ C)
Velocity at T
The Q 10 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 pathogens and spoilage organisms, most of the discussion that follows will be devoted to the effect
of low temperatures on these microorganisms. It should be remembered, however, that temperature
is related to relative humidity (RH) and that subfreezing temperatures affect RH as well as pH, and
possibly other parameters of microbial growth as well.
DEFINITIONS
The term psychrophile was coined by Schmidt-Nielsen in 1902 for microorganisms that grow at
0
◦ C.
31 This term is now applied to organisms that grow over the range of subzero to 20
◦ C, with an
optimum range of 10–15
◦ C.
47 Around 1960, the term psychrotroph (psychros, cold, and trephein, to
nourish or to develop) was suggested for organisms able to grow at 5
◦ C or below.
13,50 It is now widely
accepted among food microbiologists that a psychrotroph is an organism that can grow at temperatures
395