CITRIC encyclopedia topics

CITRIC - 5 reference results

citric acid cycle: see Krebs cycle.

The Columbia Electronic Encyclopedia Copyright © 2004.
Licensed from Columbia University Press

citric acid or 2-hydroxy-1,2,3-propanetricarboxylic acid, HO₂CCH₂C(OH)(CO₂H)CH₂CO₂H, an organic carboxylic acid containing three carboxyl groups; it is a solid at room temperature, melts at 153°C;, and decomposes at higher temperatures. It is responsible for the tart taste of various fruits in which it occurs, e.g., lemons, limes, oranges, pineapples, and gooseberries. It can be extracted from the juice of citrus fruits by adding calcium oxide (lime) to form calcium citrate, an insoluble precipitate that can be collected by filtration; the citric acid can be recovered from its calcium salt by adding sulfuric acid. It is obtained also by fermentation of glucose with the aid of the mold Aspergillus niger and can be obtained synthetically from acetone or glycerol. Citric acid is used in soft drinks and in laxatives and cathartics. Its salts, the citrates, have many uses, e.g., ferric ammonium citrate is used in making blueprint paper. Sour salt, used in cooking, is citric acid.

The Columbia Electronic Encyclopedia Copyright © 2004.
Licensed from Columbia University Press

tricarboxylic acid cycle

or Krebs cycle or citric-acid cycle

Last stage of the chemical processes by which living cells obtain energy from foodstuffs. Described by Hans Adolf Krebs in 1937, the reactions of the cycle have been shown in animals, plants, microorganisms, and fungi, and it is thus a feature of cell chemistry shared by all types of life. It is a complex series of reactions beginning and ending with the compound oxaloacetate. In addition to re-forming oxaloacetate, the cycle produces carbon dioxide and the energy-rich compound ATP. The enzymes that catalyze each step are located in mitochondria in animals, in chloroplasts in plants, and in the cell membrane in microorganisms. The hydrogen atoms and electrons that are removed from intermediate compounds formed during the cycle are channeled ultimately to oxygen in animal cells or to carbon dioxide in plant cells.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

citric acid

Colourless, crystalline organic compound (C₆H₈O₇), one of the carboxylic acids. It is present in almost all plants (especially citrus fruits) and in many animal tissues and fluids. It is one of a series of compounds involved in the physiological oxidation (see oxidation-reduction) of fats, proteins, and carbohydrates to carbon dioxide and water (see tricarboxylic acid cycle). It has a characteristic sharply sour taste and is used in many foods, confections, and soft drinks. It is added to certain foods to improve their stability in metal containers. Industrially, it is used as a water conditioner, cleaning and polishing agent, and chemical intermediate.