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(lĕv`yəlōs'), or

fruit sugar,

simple sugar found in honey and in the fruit and other parts of plants. It is much sweeter than sucrosesucrose
, commonest of the sugars, a white, crystalline solid disaccharide (see carbohydrate) with a sweet taste, melting and decomposing at 186°C; to form caramel. It is known commonly as cane sugar, beet sugar, or maple sugar, depending upon its natural source.
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 (cane sugar). It is best obtained by hydrolysis of inulin, a polysaccharide found in dahlia bulbs and the Jerusalem artichoke. Chemically it is a monosaccharide (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).
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) with the empirical formula C6H12O6. It has the same formula as glucose but differs from it 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.
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). It is often found with glucose in nature. Glucose and fructose are formed in equal amounts when sucrose is hydrolyzed by the enzyme invertase or by heating with dilute acid; the resulting equimolar mixture of fructose and glucose, called invert sugar, is the major component of honey. Fructose reacts with Fehling's solutionFehling's solution
, deep-blue, alkaline solution used to test for the presence of aldehydes (e.g., formaldehyde, HCHO) or other compounds that contain the aldehyde functional group, -CHO.
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 and can be differentiated from glucose by its reaction with lime water to form a water-insoluble precipitate, calcium fructosate. In solution, fructose exists as a ring compound in equilibrium with a straight-chain form.
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A sugar that is the commonest of ketoses and the sweetest of the sugars. It is also known as d -fructose, d -fructopyranose, and levulose fruit sugar. It is found in free state, usually accompanied by d -glucose and sucrose in fruit juices, honey, and nectar of plant glands. d -Fructose is the principal sugar in seminal fluid. See Carbohydrate

Fructose is readily utilized by diabetic animals. In persons with diabetes mellitus or parenchymal hepatic disease, the impairment of fructose tolerance is relatively small and not at all comparable to the diminution in their tolerance to glucose. See Monosaccharide

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



(fruit sugar, levulose, (β-D-fructose), a colorless crystalline substance, with a sweet taste (1.5 times sweeter than saccharose and three times sweeter than glucose) and a melting point of 102°–104°C.

Fructose is soluble in water. A monosaccharide, it occurs naturally in many fruits and vegetables, such as apples and tomatoes, and in honey (approximately 50 percent) and is a constituent of oligosaccharides and polysaccharides. The phosphates of fructose, such as fructose-l,6-diphosphate and fructose-6-phosphate, are intermediate compounds in the dark phase of photosynthesis (Calvin cycle), in major metabolic processes (glycolysis, alcoholic fermentation), and in the biosynthesis of carbohydrates.

Fructose is a valuable food product and is easily assimilated by the organism. It is obtained from fruits by the hydrolysis of saccharose and inulin, as well as by the action of alkalies on D-glucose. In addition to the furanose (natural) form, the open ketone form and other tautomeric forms of fructose are known. Fructose is used in the food-processing industry and in medicine. Fructose-1,6-diphosphate is a drug administered to persons suffering from shock or various heart conditions.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


C6H12O5 The commonest of ketoses and the sweetest of sugars, found in the free state in fruit juices, honey, and nectar of plant glands. Also known asD-fructopyranose.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


a white crystalline water-soluble sugar occurring in honey and many fruits. Formula: C6H12O6
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005