96 ◾ Fundamental Food Microbiology
The sporulation process, as discussed previously, involves irreversible cellular differentiation processes in an unfavorable environment and is regulated and expressed by a large number
of genes. The functions of many genes have been studied with mutants of Bacillus subtilis (spo
mutants) that block formation of different components during the sporulation process. Expression
of these functional genes is regulated by the genes, coding for specific sigma factors (δ). In a favorable environment, germination and outgrowth are also mediated through other genes that enable
an endospore to enter into the cell division cycle. 2
importance of Spores in Food
Spore formation, especially by molds and some bacterial species, enables them to survive for a long
time and provides a basis for the continuation of the species. It also provides a means of their easy
dissemination by dust and air in the environment. 1,2 In this manner, foods can be contaminated
by their spores rather easily from various sources. In a suitable food environment, spores germinate, grow, and produce undesirable (or desirable) effects. Mold and yeast spores are relatively
sensitive to heat, and their growth can also be prevented by storing foods in the absence of air.
Many species of Bacillus, Clostridium, and Desulfotomaculum are associated with food spoilage and foodborne diseases. As a result of high heat resistance, the spores are of special interest
and importance in food processing. Special attention must be given to processing and preserving
the foods so that the spores are either destroyed or prevented from undergoing germination and
outgrowth because ungerminated spores cannot cause spoilage or foodborne disease. Another
possibility is to induce the spores to germinate and outgrow and then expose them to an antibacterial treatment to destroy them. Superdormant spores of the spoilage and pathogenic species pose
another problem. As they are not detected normally with the other spores, a processing condition could be wrongly adopted with the idea that it will eliminate all spores. Subsequently, these
surviving superdormant spores can germinate, outgrow, and grow, and can either cause the food
to spoil or make it unsafe. As it is impossible to destroy all spores in many foods, several specific
methods or a combination of processing and preservation methods have been developed to overcome problems of spores in food. 1–3
In the canning of low-acid foods, very high heat treatment is employed to achieve commercial
sterility that kills spores of all pathogenic bacteria and most spoilage bacteria (except some thermophilic spoilage bacteria). To prevent germination of spores, depending on the food type, nitrites (in
processed meat), low pH (acid products), low A W , or high salt are used. High hydrostatic pressure is
currently being studied to determine its spore destruction potential. Although spores of molds are
destroyed at relatively low pressure (<400 MPa), spores of many pathogenic and spoilage bacteria
need a combination of very high pressure (≥700 MPa) and high temperature (≥90°C) to obtain
commercial sterility. 7 It has been known for long that spores of many foodborne bacteria can be activated to germination and outgrowth at a lower pressure range. Following such a pressure treatment,
another antibacterial treatment, such as another pressure cycle, heat, or antimicrobial preservative
can be given to destroy the germinated and outgrown spores before cell growth starts. The influence
of several parameters on germination, such as pressure range, time of pressurization, pressurization temperature, and holding time following pressurization, is currently being studied. 8 Table 9.1
presents the results of a study. It can be seen that under any given condition, germination induction
varies greatly with species. In general, germination increases with pressure and temperature within
the range studied. More such studies with many strains of the important species will provide more
meaningful data to determine the potential of such treatment to control bacterial spores in food.
The sporulation process, as discussed previously, involves irreversible cellular differentiation processes in an unfavorable environment and is regulated and expressed by a large number
of genes. The functions of many genes have been studied with mutants of Bacillus subtilis (spo
mutants) that block formation of different components during the sporulation process. Expression
of these functional genes is regulated by the genes, coding for specific sigma factors (δ). In a favorable environment, germination and outgrowth are also mediated through other genes that enable
an endospore to enter into the cell division cycle. 2
importance of Spores in Food
Spore formation, especially by molds and some bacterial species, enables them to survive for a long
time and provides a basis for the continuation of the species. It also provides a means of their easy
dissemination by dust and air in the environment. 1,2 In this manner, foods can be contaminated
by their spores rather easily from various sources. In a suitable food environment, spores germinate, grow, and produce undesirable (or desirable) effects. Mold and yeast spores are relatively
sensitive to heat, and their growth can also be prevented by storing foods in the absence of air.
Many species of Bacillus, Clostridium, and Desulfotomaculum are associated with food spoilage and foodborne diseases. As a result of high heat resistance, the spores are of special interest
and importance in food processing. Special attention must be given to processing and preserving
the foods so that the spores are either destroyed or prevented from undergoing germination and
outgrowth because ungerminated spores cannot cause spoilage or foodborne disease. Another
possibility is to induce the spores to germinate and outgrow and then expose them to an antibacterial treatment to destroy them. Superdormant spores of the spoilage and pathogenic species pose
another problem. As they are not detected normally with the other spores, a processing condition could be wrongly adopted with the idea that it will eliminate all spores. Subsequently, these
surviving superdormant spores can germinate, outgrow, and grow, and can either cause the food
to spoil or make it unsafe. As it is impossible to destroy all spores in many foods, several specific
methods or a combination of processing and preservation methods have been developed to overcome problems of spores in food. 1–3
In the canning of low-acid foods, very high heat treatment is employed to achieve commercial
sterility that kills spores of all pathogenic bacteria and most spoilage bacteria (except some thermophilic spoilage bacteria). To prevent germination of spores, depending on the food type, nitrites (in
processed meat), low pH (acid products), low A W , or high salt are used. High hydrostatic pressure is
currently being studied to determine its spore destruction potential. Although spores of molds are
destroyed at relatively low pressure (<400 MPa), spores of many pathogenic and spoilage bacteria
need a combination of very high pressure (≥700 MPa) and high temperature (≥90°C) to obtain
commercial sterility. 7 It has been known for long that spores of many foodborne bacteria can be activated to germination and outgrowth at a lower pressure range. Following such a pressure treatment,
another antibacterial treatment, such as another pressure cycle, heat, or antimicrobial preservative
can be given to destroy the germinated and outgrown spores before cell growth starts. The influence
of several parameters on germination, such as pressure range, time of pressurization, pressurization temperature, and holding time following pressurization, is currently being studied. 8 Table 9.1
presents the results of a study. It can be seen that under any given condition, germination induction
varies greatly with species. In general, germination increases with pressure and temperature within
the range studied. More such studies with many strains of the important species will provide more
meaningful data to determine the potential of such treatment to control bacterial spores in food.