DEHYDRATION as method — a way of elimination of water from various materials for the purpose of receiving the dehydrated product; it is widely applied in histology, in medical, chemical and pharmaceutical, food and other industries. The lake is made for the purpose of reduction of the weight (weight) of material, increase in its stability and creation of conditions for long-term storage.
The island is carried out by various ways: 1) mechanically — without change of aggregate state of moisture; 2) with change of aggregate state of moisture, i.e. by transition of liquid to steam (see. Evaporation ) or transition of ice to steam, passing a liquid phase (see. Lyophilizing ).
At O. by the first way for removal of moisture centrifuges, various types of press and filters are used. At O. in the second way for phase change of liquid or ice in steam it is necessary to bring heat to material. The second way O. is widely used during the receiving dry medical drugs and pharmaceuticals (antibiotics, blood substitutes, extracts of medicinal plants, etc.). Vacuum drying ovens, drum, tape, aero gushing and spray driers are for this purpose used. Lyophilizing is applied by hl. obr. during the receiving proteinaceous, fermental and other medical drugs. Feature of dehydration of medical drugs is that many of them in a dry form shall be sterile, it defines a design of the drying apparatuses used in the medical industry. Spray driers are used when O. subject thermosensitive drugs (krovezamenyayushchy liquids, antibiotics, enzymes, solutions of sugars, etc.). The essence of process of O. consists in the raspylitelny way that initial solution by means of quickly rotating disks (18 000 — 24 000 rpm) or nozzles is dispersed in volume of the drying chamber and its drop, getting to a flow of heated air, instantly evaporate since between the heat carrier and an object O. there is intensive warm also a mass exchange. By selection of such parameters O. as air consumption, a consumption of solution, air temperature on an entrance and escaping of the drying chamber, it is possible to regulate physical. - chemical properties of dry drugs, including the volume weight (weight), particle sizes, residual humidity, etc. Additional O. to the constant weight (weight) allows to define residual humidity of dry drugs, edges for many medical drugs shall not exceed 1-2%.
Use of dehydration in histologic practice
In histologic practice of O. is applied to elimination of water from pieces of bodies and fabrics in the course of preparation gistol, drugs and to dehydration of the reactants used in histologic researches (see. Histologic methods of a research ).
Pieces of bodies and fabrics before paraffin embedding or in photoxylin for their best treatment dehydrate by means of ether, acetone, chloroform or a xylol, however most often for this purpose use ethanol of the ascending concentration (from 50% to absolute alcohol). The recorded pieces of body or fabric wash out in running water and consistently place in vessels with ethanol of the ascending concentration, maintaining in each vessel till some hours. Ethanol and other organic solvents before the use in turn dehydrate by means of anhydrous (calcinated till white color) a copper vitriol or synthetic zeolite (aluminosilicate), to-rye «select» water from the processed liquid reactant.
Use of dehydration for conservation of products
is widely applied by O. to conservation of foodstuff. Advantage of conservation of food stuffs in the way of O. before other methods of conservation is reduction of their volume and weight that leads to decrease in economic costs of construction of warehouse, packaging and transportation.
The foodstuff preserved by method O. remains rather long time, without spoiling since removal of moisture from them creates unfavorable conditions for life activity of microorganisms and course of enzymatic and non-enzymatic processes.
The way O. of foodstuff influences their organoleptic properties, outward and ability to swelling at an ovodneniya. The lyophilizing of berry which is dried up by method, fruits, fish, meat unlike the products which are dried up by method of thermal drying well keep the initial qualities — color, aroma, taste, a form and the sizes. In the course of an ovodneniye of the food stuffs which are dried up by method of freeze drying initial humidity of a product almost completely is recovered, and under favorable conditions and cellular turgor, especially if decrease in temperature was carried out to freezing time of a product quickly and the formed small kristallik of ice did not break structure of fabrics (see. the Foodstuff lyophilized and sublimated ).
Thermal drying even if it is carried out at moderate temperatures (apprx. 60 °), leads to jump of structure of fabrics, to their so-called shrinkage and change of a form of a product, influences on their organoleptic and tastes, and also nutrition value. The ovodneniye of foodstuff after thermal drying requires their long soaking or processing at high temperatures (cooking).
Drying of food stuffs at high temperatures (60 °) gives to change of quality of a product owing to melting of fat and a kleysterization of starch above. Degree of a denaturation of proteins at such drying is higher, than at sublimation drying (lyophilizing) though comprehensibility of nitrogenous substances at food the products which underwent high-temperature drying depends on a way O a little.
Various ways O. of foodstuff differently affect content of vitamins in them. At sublimation drying in many products about 80% ascorbic to - you whereas at thermal drying in strawberry, e.g., remains apprx. 3%, and in raspberry to 1% of initial quantity ascorbic to - you remain.
Bibliography: Burich O. and Berki F. Drying of fruits and vegetables, the lane with Wenger., M., 1978; Volkova O. V. and Yelets Yu. K. Fundamentals of histology and histologic equipment, page 135, M., 1971; Genin S.A. Technology of drying of potatoes, vegetables and fruits, M., 1971; Ginzburg A. S. Bases of the theory and technology of drying of foodstuff, M., 1973; Histology, under the editorship of V. G. Yeliseyev, etc., M., 1972; Golubev JI., Sazhin B. S. and Valashek E. P. Drying in chemical pharmaceutical industry, M., 1978, bibliogr.; L y-kov A. V. The theory of drying, M. — L., 1950, bibliogr.; A small workshop on cytology, under the editorship of Yu. S. Chentsov, page 257, M., 1977; Merkulov G. A. Course of the patologogistologichesky equipment, page 24, etc., L., 1969; Podolsk M. V. Drying of blood preparations and blood substitutes, M., 1973, bibliogr.; Soboleva A. D. Reaction of cells and fabrics to dehydration, Novosibirsk, 1975; Tkachenko E. C. The nutritional and biological value of the foodstuff preserved by method of sublimation, M., 19-66, bibliogr.
M. V. Podolsky; L. S. Sutulov (gist.), E. A. Lebedeva (pitas.).