Fundamental Food Microbiology, Third Edition - Fuad Fathir

MICROBIAL SPORULATION AND GERMINATION 99
Many species of Bacillus, Clostridium, and Desulfotomaculum are associated
with food spoilage and foodborne diseases. Due to 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 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. 1,2
In the canning of low-acid food, very high heat treatment is employed to achieve
commercial sterility that kills spores of all pathogenic bacteria and most spoilage
bacteria (except some of thermophilic spoilage bacteria). To prevent germination of
spores, depending on the food type, nitrite (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. 5 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. 6 Table 8.1 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.
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VI. CONCLUSION
Spore formation by certain yeasts, molds, and bacterial species is a means of survival
and continuation of the life process. In yeasts and molds, sporulation occurs by
asexual and sexual process; in bacteria, it occurs through differentiation, regulated
and expressed by many genes.
Spore formation enables the dissemination of the species widely in the environment
as well as contamination of foods. Their growth in food can be undesirable