3. Read and translate the text. Carbohydrates

Carbohydrates are one of three great classes of foods which are very important from a physiological standpoint since they include the sugars and the starches. In addition to starches and sugars the term carbohydrate includes cellulose. Carbohydrates contain three tasteless elements: carbon, hydrogen and oxygen.

Carbohydrates comprise one of the major groups of naturally occurring organic substances. They are found in all parts of celluiar material as both structural and functional components. The dry weight of plants is typically composed of 50 to 80 % of the polymeric carbohydrate cellulose. Carbohydrates are the structural backbone of the nucleic acids, RNA and DNA, and are the sugars that provide the storehouse for energy derived from the sun through photosynthesis.

it's worth mentioning that isolation, purification, and modification of carbohydrates arc the basis for many important industries. Wood, when chemically modified through pulping operations, becomes the source of paper. Sugar and starch products derived from plant materials play a major role in nutrition and the related food — processing industries.

Carbohydrates are defined precisely as compounds with the molecular formulas C_m(H₂0)_n. There are several ways of classifying the carbohydrates. In general they form two classes: those that are sweet, crystalline solids, called sugars; and those that are tasteless noncrystalline solids, called starches and celluloses. Sugars, also known as saccharides, are generally treated as the typical carbohydra­tes. From their chemical behaviour with water (hydrolysis), carbohydrates may be classified according to the number of saccharide group in their molecules. Monosaccharides arc carbohydrates which usually possess three to nine carbon atoms. The connection of two or more monosaccharides through oxygen bridges leads to oligosaccharides and to polysaccharides.

D-Glucose is the most common monosaccharide, and it may be the most abundant organic compound in nature. It occurs free in blood (blood sugar) and numerous other body fluids and in plant juices (grape sugar), and it is the major monosaccharide component of many oligosaccharides and polysaccharides. Glucose is metabolized directly by the body, ft is obtained commercially by the hydrolysis of starch followed by crystallization from an aqueous solution.

It is often important to discover if glucose is present in foods, or in urine where it is the only sugar of physiological significance. There the presence of glucose indicates glycosuria, the chief symptom of diabetes. Glucose is found in the blood to the extent of about 0.1 %, although after meals this amount may be greatly increased. Insulin is supposed to control the utilization of glucose.

Sucrose, the common table sugar, is a disaccharide composed of the two monosaccharides d-glucose and d-fructose bonded together. It is obtained from sugar beets and sugar cane, and it is one of the major industrial organic products.

Lactose (milk sugar) is a disaccharide which is present in the milk of mammals. It is composed of d-galactose and d-glucose. Lactose is commonly obtained from whey, a byproduct in the manufacture of cheese.

Carbohydrates obtained by the reduction of carbonyl to hydroxy groups in monosaccharides are known as alditols. The alditols d- mannitol and d-glucitol (sorbitol) are used commercially as wetting agents and sweeteners.