Microorganisms and Viruses

Even before the discovery of the microbial world, heat was used to control microorganisms. For example, Aristotle (384-322 B.C.) advised Alexander the Great to have his armies boil their drinking water to prevent disease. Today heat treatment is still one of the most useful methods of microbial control, because it is fast, reliable, and inexpensive relative to most other methods and it does not introduce potentially toxic substances into the material being treated.

Some types of heat treatment, such as autoclaving, are used to sterilize products, whereas other treatments, such as pasteurization, are used to decrease the numbers of microorganisms. Table 5.2 summarizes the methods, limitations, and uses of heat to control microorganisms and viruses.

Moist Heat

Moist heat, such as boiling water and pressurized steam, destroys microorganisms by coagulating their proteins irreversibly. Boiling (100°C) for 10 minutes readily destroys most microorganisms and viruses. The notable exception is endospores, including those of the food-poisoning bacteria Clostridium perfringens and C. botu-linum, which can survive many hours of boiling. Pressurized

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