Biodegradation of perishable foods takes place naturally unless some stratagem is adopted to prevent or delay this process, Perishable foods can, for example, be frozen, chilled, dried or placed in ambient - or controlled-atmosphere storage (see Table).

According to international agreements, frozen products should be held at temperatures lower than -12°C, at which significant biodegradation cannot take place (Economic Commission for Europe, 1991; Council of the European Communities, 1991), When product temperature rises above the -12°C threshold for carriage the risk of biodeterioration becomes greater, and at about -10°C actual biodeterioration can begin, with eventual detectable effects.

Many products are carried chilled (Economic Commission for Europe, 1991), The respiration of fruits and vegetables generates heat, uses oxygen and creates carbon dioxide and water vapor, and ethylene gas may be produced which accelerates ripening, Chilling slows these processes, The aim is to reduce the product’s temperature and maintain it at the lowest possible value without causing damage.

Controlled-atmosphere carriage is used with respiring fruits, such as bananas, where both the temperature and the gas composition in contact with the product must be held very precisely to ensure that ripening does not occur in an uncontrolled way, Both chilling and atmosphere control are delicate procedures demanding fine control.

Dried products can remain stable, without significant biological activity, but they do deteriorate if they lack appropriate packaging to prevent them from absorbing or releasing water vapor, If bulk products, such as grain, that cannot be packaged readily are loaded at high ambient temperature, the water content should be reduced more than is necessary at lower temperatures to maintain product stability (Milton and Jarrett, 1970; Milton and Pawsey, 1988).

The stability of other products when stored under ambient conditions is largely determined by their prior processing and packaging, Sterile packaged products, such as canned foods, are stable over a wide temperature range.