denying moisture to the microorganisms when the temperature is below freezing. The
rate of destruction by high temperatures depends upon the time and temperature, the
presence of moisture, the kind of microorganisms present, the number of
microorganisms present, and the pH of the medium in which the microorganisms are
located.
c. Chemical Agents. There are many chemical agents that may inhibit or kill
microorganisms. Soap and detergents are important because they will physically
remove microorganisms, and they also have an antiseptic action. Alkalies are effective
by altering the pH. Alcohol in 70 percent concentration is germicidal. Organic acids,
such as acetic and lactic acid, are widely used as antiseptics. Chlorine is the most
widely used of all disinfectants. Its efficiency is reduced by the presence of organic
materials. Chlorine is added to drinking water in quantities varying from 0.25 to 10 ppm
(parts per million). Chlorine is extensively used in dairy plants and other food
processing plants to disinfect vats, pipelines, and many other pieces of equipment.
MD0703
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