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milk sugar,white crystalline disaccharide (see carbohydratecarbohydrate,
any member of a large class of chemical compounds that includes sugars, starches, cellulose, and related compounds. These compounds are produced naturally by green plants from carbon dioxide and water (see photosynthesis).
..... Click the link for more information. ). It has the same empirical formula (C12H22O11) as sucrose (cane sugar) and maltose but differs from both in structure (see isomerisomer
, in chemistry, one of two or more compounds having the same molecular formula but different structures (arrangements of atoms in the molecule). Isomerism is the occurrence of such compounds. Isomerism was first recognized by J. J. Berzelius in 1827.
..... Click the link for more information. ). It yields the simple sugarssugar,
compound of carbon, hydrogen, and oxygen belonging to a class of substances called carbohydrates. Sugars fall into three groups: the monosaccharides, disaccharides, and trisaccharides. The monosaccharides are the simple sugars; they include fructose and glucose.
..... Click the link for more information. D-glucose and D-galactose on hydrolysishydrolysis
, chemical reaction of a compound with water, usually resulting in the formation of one or more new compounds. The most common hydrolysis occurs when a salt of a weak acid or weak base (or both) is dissolved in water.
..... Click the link for more information. , which is catalyzed by lactase, an enzyme found in gastric juice. People who lack this enzyme after childhood cannot digest milkmilk,
liquid secreted by the mammary glands of female mammals as food for their young. The milk of the cow is most widely used by humans, but the milk of the mare, goat, ewe, buffalo, camel, ass, zebra, reindeer, llama, and yak is also used.
..... Click the link for more information. and are said to be lactose intolerant. Lactose is formed in the mammary glands of all lactating animals and is present in their milk. It is produced commercially as a byproduct of milk processing. When milk sours, the lactose in it is converted by bacteria to lactic acid. Lactose is less sweet-tasting than sucrose and is not found in plants.
Milk sugar or 4-O-β- d -galactopyranosyl- d -glucose. This reducing disaccharide is obtained as the α- d anomer (see formula, where the asterisk indicates a reducing group); the melting point is 202°C (396°F). Lactose is found in the milk ofmammals to the extent of approximately 2–8%. It is usually prepared from whey, which is obtained by a by-product in the manufacture of cheese. Upon concentration of the whey, crystalline lactose is deposited.
(milk sugar), C12H22O11, a disaccharide, formed from D-galactose and D-glucose radicals; it exists in the a- and β- forms. Crystalline lactose is obtained in three modifications: α-form (melting point, 223°C), β-form (melting point, 252°C), and the α-form monohydrate (melting point, 202°C). Lactose is soluble in water, diluted ethyl alcohol, and pyridine and insoluble in ether and absolute alcohol; it separates into galactose and glucose during acidic hydrolysis.
Lactose occurs in free form (2–8.5 percent) in the milk of all mammals and is included in the composition of oligosaccharides, glycolipides, and glycoproteins. It has also been found in the pollen tubes of some plants. Lactose biosynthesis is effected by the enzyme galactosyl transferase, which catalyzes the transfer of the galactose radical from uridine diphosphate galactose to D-glucose. The enzymatic hydrolysis of lactose proceeds upon action of β-galactosidase. The absence of galactosidase in the mucous membrane of a newborn’s intestines is a hereditary disease that may lead to death if lactose is not excluded from the diet.
D. M. BELEN’KII