The preservation of foods by drying is probably the oldest food preservation process practiced by humans. It is believed that many foods, especially grains and fruits of high sugar content, were preserved by primitive peoples by allowing them to dry in the sun. Spices and fish, cut into thin strips, were also preserved in this manner.
There are number of different methods of drying foods for preservation. The most important are sun drying, tunnel or cabinet drying, drum drying, spray drying and freeze drying.Foods to be dried must be washed, and some peeled and cut. Others may be pre cooked. Cut fruits are subjected to darkening through enzymes action and must be either blanched or treated with salts or sulfur dioxide. However if treated with sulfur dioxide, the product must be so labeled, because of known allergenic reactions in some consumers. Certain vegetables may be pretreated in the same manner. Sulfuring may also be required to limit non enzymatic browning (the Maillard reactions). Browning refers to the development of brown color.
Various dried eggs products are also subject to browning and also susceptible to the development of off flavors. In this case, the reaction involves a combination of small amount of glucose, which is naturally present, with proteins. Because of this, dried eggs products, especially egg whites, may be treated with glucose oxidase and catalase. The glucose oxidase converts glucose to gluconic acid (which does not combine with amino groups) and hydrogen peroxide. The purpose of the catalase is to convert the undesirable peroxide to water and oxygen. The elimination of glucose may also be done by natural fermentation using microbes. However this process can be considered unsanitary and in order to avoid product spoilage and even food poisoning, it is necessary to hold the product at 130 degree F for several hours after drying.Pretreatment before Process of Drying
