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From the moment an edible raw material is harvested, gathered, caught or slaughtered, it undergoes progressive deterioration. The process may be very slow, as with seed or nuts, or so rapid as with milk or fish that the food becomes virtually useless in a matter of hours. Bacteria, yeasts, moulds, insects and rodents are in constant competition with man for his food supply. Foods are also subject to destruction by nearly every variable in the natural environment. Heat and cold, light, oxygen, moisture, dryness and natural enzymes within the food, all tend to cause deterioration
Efforts to preserve food aim to minimize the factors that lead to deterioration by processes such as drying, salting, pickling, sugaring, smoking, fermentation, even in refrigeration, packaging and frozen storage. A recently developed preservation technique is food irradiation which appears to hold considerable promise for some purposes in both developing and developed countries.
Most food-borne diseases are microbial in origin, but a bewildering array of biological and chemical contaminants can make food either inedible, dangerous to eat or lethal. Mycotoxins produced by fungi cause illness and numerous deaths every year, and leads to the loss of substantial amounts of food. The ever-increasing complexity of modern industrial society and the wide-ranging nature of the international food trade have increased the risk of the contamination of foods by chemical and biological agents. The contaminants may arise from environmental or industrial pollution (e.g. mercury, lead, arsenic), from agricultural technology (e.g. pesticide or veterinary drug residues) and from food processing practices (e.g. nitrosamines, polynuclear hydrocarbons). If any portion of the food chain should become contaminated, the contaminant is likely to enter the human food supply, presenting a potential hazard to human health as well as an impediment to food trade.
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