dehydration

dehydration

Method of food preservation in which moisture (primarily water) is removed. Dehydration inhibits the growth of microorganisms and often reduces the bulk of food. It is an ancient practice, used by prehistoric peoples in sun-drying seeds, by North American Indians in sun-drying meat strips, and by the Japanese in drying fish and rice. It was used to prepare troop rations in World War II, and in recent decades campers and relief agencies have discovered its advantages. Commercial dehydration equipment includes tunnel dryers, kilns, and vacuum dryers. A combination of dehydration and freezing is used in the process of freeze-drying, whereby solid food remains frozen while its liquid escapes as vapour. The dairy industry is one of the largest producers of dehydrated foods, including whole milk, skim milk, and eggs.

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dehydration

Loss of water, almost always along with salt, from the body, caused by restricted water intake or excessive water loss. Early symptoms of water deprivation are thirst, decreased saliva, and impaired swallowing. (When more electrolytes than water are lost, osmosis pulls water into cells, and there is no thirst.) Later, tissues shrink, including the skin and eyes. Mild fever rises as plasma volume and cardiac output decrease, and perspiration decreases or stops, greatly reducing heat loss. Urine output falls, and the kidneys cannot filter wastes from the blood. Irreversible shock can occur at this point. The cause of dehydration is treated first; then water and electrolytes must be given in the correct proportions.