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[lak-tohs] /ˈlæk toʊs/
Biochemistry. a disaccharide, C 12 H 22 O 11 , present in milk, that upon hydrolysis yields glucose and galactose.
a white, crystalline, sweet, water-soluble commercial form of this compound, obtained from whey and used in infant feedings, in confections and other foods, in bacteriological media, and in pharmacology as a diluent and excipient.
Also called milk sugar, sugar of milk.
Origin of lactose
First recorded in 1855-60; lact- + -ose2 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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Examples from the Web for lactose
Historical Examples
  • The estimation of the butter being accomplished, it is frequently needful to determine the amount of lactose present.

    Legal Chemistry A. Naquet
  • Control of casein or lactose, on the contrary, is not nearly so practicable.

    The Book of Cheese Charles Thom and Walter Warner Fisk
  • These are all characteristic reactions of lactose or milk sugar.

  • Levulose, lactose, and some others are occasionally met with.

    A Manual of Clinical Diagnosis James Campbell Todd
  • The carbohydrates, comprising 4.88% to 5% of the solids in milk, occur as lactose or milk sugar.

    Dietetics for Nurses Fairfax T. Proudfit
  • lactose exists in milk and has the same formula as cane-sugar.

    Encyclopedia of Diet Eugene Christian
  • Galactose occurs in the animal kingdom as one of the constituents of lactose, or milk-sugar.

    The Chemistry of Plant Life Roscoe Wilfred Thatcher
  • There are many varieties of sugar in common use, viz.: cane sugar, grape sugar or glucose, and sugar of milk (lactose).

  • Dextrose, saccharose and lactose are the most used, though many others are used for special purposes.

    The Fundamentals of Bacteriology Charles Bradfield Morrey
  • The mass curdles and separates into a solid curd (proteid and fat) and a clear fluid (the whey), which contains the lactose.

    A Practical Physiology Albert F. Blaisdell
British Dictionary definitions for lactose


/ˈlæktəʊs; -təʊz/
a white crystalline disaccharide occurring in milk and used in the manufacture of pharmaceuticals and baby foods. Formula: C12H22O11 Also called milk sugar
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for lactose

sugar from milk, 1858, from French, coined by French chemist Marcelin-Pierre-Eugène Berthelot (1827-1907) from Latin lac (genitive lactis) "milk" (see lactation) + chemical suffix -ose (2).

Online Etymology Dictionary, © 2010 Douglas Harper
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lactose in Medicine

lactose lac·tose (lāk'tōs')

  1. A disaccharide in milk that hydrolyzes to yield glucose and galactose. Also called milk sugar.

  2. A white crystalline substance obtained from whey and used in infant foods and in pharmaceuticals as a diluent and excipient. Also called milk sugar.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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lactose in Science
  1. A white crystalline disaccharide consisting of a glucose and a galactose molecule, found in milk and used in the manufacture of various other foods. Chemical formula: C12H22O11.

  2. The inability to digest lactose properly is called lactose intolerance. It is caused by a deficiency of the enzyme lactase and marked by abdominal cramping and other symptoms after ingesting lactose.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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