Microorganisms are often responsible for the rapid spoilage of foods. Of special concern is the growth of bacteria such as Clostridium botulinum which generate poisonous products. Enzymatic action in stored food produces changes which can adversely affect the appearance of food or its palatability. Spoilage by chemical action results from the reaction of one group of components in the food with others or with its environment, as in corrosion of the walls of metal containers or the reaction of fats with oxygen in the air to produce rancidity. Sprouting is a naturally occurring phenomenon in stored potatoes, onions, carrots, beets, and similar root vegetables.
Insect infestation is a problem of importance chiefly in stored grain.
The presence of parasitic organisms such as Trichinella spiralis in pork introduces another factor which must be dealt with in food processing. To permit the storage of food for long periods of time, a method of preservation must accomplish the destruction of microorganisms and inhibition of enzymatic action. Food treated in this manner and protected from recontamination by aseptic methods of packaging and containment presumably could be stored for long periods without refrigeration. Less severe thermal treatment as by blanching or scalding serves to inactivate enzymes. It furnishes a means of destroying insects in stored grain products as well as certain parasitic organisms present in meats.