ABSTRACT
The physical factors discussed in this chapter can affect the growth and/or survival of microorganisms, hence they can be used for microbial control in food or its surroundings. Occasionally, the theoretical straight line is a curve showing that some cells in the population are more resistant to the lethal effect than are other cells. The decimal reduction time is affected by several factors, which need to be considered when using heat as a lethal agent: In the food industry, high temperatures are applied in several ways to kill microorganisms. It is possible that some cells will die, but for all practical purposes, chilling and freezing should never be considered as techniques for killing microorganisms. However, ultra-violet light and atomic radiations such as x-rays and gamma-rays can kill microorganisms. Operators should not be present when the lights are in use because of their danger to eyesight, and their carcinogenic effect on skin..
