Citric Acid
<p ><b>Citric acid</b> is a <a href="http://en.wikipedia.org/wiki/Weak_acid" title="Weak acid" class="mw-redirect" >weak</a> <a href="http://en.wikipedia.org/wiki/Organic_acid" title="Organic acid" >organic acid</a>. It is a natural <a href="http://en.wikipedia.org/wiki/Preservative" title="Preservative" >preservative</a>/conservative and is also used to add an acidic, or <a href="http://en.wikipedia.org/wiki/Taste#Sourness" title="Taste" >sour</a>, taste to foods and<a href="http://en.wikipedia.org/wiki/Soft_drink" title="Soft drink" >soft drinks</a>. In <a href="http://en.wikipedia.org/wiki/Biochemistry" title="Biochemistry" >biochemistry</a>, the <a href="http://en.wikipedia.org/wiki/Conjugate_base" title="Conjugate base" class="mw-redirect" >conjugate base</a> of citric acid, citrate, is important as an intermediate in the <a href="http://en.wikipedia.org/wiki/Citric_acid_cycle" title="Citric acid cycle" >citric acid cycle</a>, and therefore occurs in the <a href="http://en.wikipedia.org/wiki/Metabolism" title="Metabolism" >metabolism</a> of virtually all <a href="http://en.wikipedia.org/wiki/Life" title="Life" >living things</a>.</p>
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Citric acid can be added to e.g. <a href="http://en.wikipedia.org/wiki/Ice_cream" title="Ice cream" >ice cream</a> as an emulsifying agent to keep fats from separating, to <a href="http://en.wikipedia.org/wiki/Caramel" title="Caramel" >caramel</a> to prevent sucrose crystallization, or to recipes in place of fresh lemon juice. Citric acid is used with <a href="http://en.wikipedia.org/wiki/Sodium_bicarbonate" title="Sodium bicarbonate" >sodium bicarbonate</a> in a wide range of <a href="http://en.wikipedia.org/wiki/Effervescence" title="Effervescence" >effervescent</a> formulae, both for ingestion (<i >e.g.</i>, powders and tablets) and for personal care (<i >e.g.</i>, <a href="http://en.wikipedia.org/wiki/Bath_salts" title="Bath salts" >bath salts</a>, <a href="http://en.wikipedia.org/wiki/Bath_bomb" title="Bath bomb" >bath bombs</a>, and cleaning of <a href="http://en.wikipedia.org/wiki/Petroleum" title="Petroleum" >grease</a>). </p>
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Citric acid is also often used in cleaning products and sodas or fizzy drinks.</p>
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Citric acid is a commodity chemical, and more than a million tonnes are produced every year by fermentation. It is used mainly as an acidifier, as a flavoring, and as a <a href="http://en.wikipedia.org/wiki/Chelating_agent" title="Chelating agent" class="mw-redirect" >chelating agent</a>.</p>
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Citric acid exists in greater than trace amounts in a variety of fruits and vegetables, most notably <a href="http://en.wikipedia.org/wiki/Citrus" title="Citrus" >citrus fruits</a>. Lemons and <a href="http://en.wikipedia.org/wiki/Lime_(fruit)" title="Lime (fruit)" >limes</a> have particularly high concentrations of the acid; it can constitute as much as 8% of the dry weight of these fruits (about 47 <a href="http://en.wikipedia.org/wiki/Gram_per_litre" title="Gram per litre" >g/L</a> in the juices<sup id="cite_ref-8" class="reference" ><a href="http://en.wikipedia.org/wiki/Citric_acid#cite_note-8" >[9]</a></sup>). The concentrations of citric acid in citrus fruits range from 0.005 <a href="http://en.wikipedia.org/wiki/Molarity" title="Molarity" class="mw-redirect" >mol/L</a> for oranges and grapefruits to 0.30 mol/L in lemons and limes. Within species, these values vary depending on the <a href="http://en.wikipedia.org/wiki/Cultivar" title="Cultivar" >cultivar</a> and the circumstances in which the fruit was grown.</p>
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The dominant use of citric acid is as a <a href="http://en.wikipedia.org/wiki/Flavoring" title="Flavoring" class="mw-redirect" >flavoring</a> and preservative in food and beverages, especially soft drinks.<sup id="cite_ref-ullmann_4-2" class="reference" ><a href="http://en.wikipedia.org/wiki/Citric_acid#cite_note-ullmann-4" >[5]</a></sup> Within the <a href="http://en.wikipedia.org/wiki/European_Union" title="European Union" >European Union</a> it is denoted by <a href="http://en.wikipedia.org/wiki/E_number" title="E number" >E number</a> <b>E330</b>. Citrate salts of various metals are used to deliver those minerals in a biologically available form in many <a href="http://en.wikipedia.org/wiki/Dietary_supplement" title="Dietary supplement" >dietary supplements</a>. The <a href="http://en.wikipedia.org/wiki/Buffering_agent" title="Buffering agent" >buffering</a> properties of citrates are used to control <a href="http://en.wikipedia.org/wiki/PH" title="PH" >pH</a> in household cleaners and <a href="http://en.wikipedia.org/wiki/Pharmaceutical" title="Pharmaceutical" class="mw-redirect" >pharmaceuticals</a>. In the United States the purity requirements for citric acid as a food additive are defined by the <a href="http://en.wikipedia.org/w/index.php?title=Food_Chemical_Codex&action=edit&redlink=1" class="new" title="Food Chemical Codex (page does not exist)" >Food Chemical Codex</a>, which is published by the <a href="http://en.wikipedia.org/wiki/United_States_Pharmacopoeia" title="United States Pharmacopoeia" class="mw-redirect" >United States Pharmacopoeia</a> (USP).</p>
<h3 >[<a href="http://en.wikipedia.org/w/index.php?title=Citric_acid&action=edit§ion=9" title="Edit section: Foods, other" >edit</a>]Foods, other</h3>
<p >Citric acid can be added to e.g. <a href="http://en.wikipedia.org/wiki/Ice_cream" title="Ice cream" >ice cream</a> as an emulsifying agent to keep fats from separating, to <a href="http://en.wikipedia.org/wiki/Caramel" title="Caramel" >caramel</a> to prevent sucrose crystallization, or to recipes in place of fresh lemon juice. Citric acid is used with <a href="http://en.wikipedia.org/wiki/Sodium_bicarbonate" title="Sodium bicarbonate" >sodium bicarbonate</a> in a wide range of <a href="http://en.wikipedia.org/wiki/Effervescence" title="Effervescence" >effervescent</a> formulae, both for ingestion (<i>e.g.</i>, powders and tablets) and for personal care (<i>e.g.</i>, <a href="http://en.wikipedia.org/wiki/Bath_salts" title="Bath salts" >bath salts</a>, <a href="http://en.wikipedia.org/wiki/Bath_bomb" title="Bath bomb" >bath bombs</a>, and cleaning of <a href="http://en.wikipedia.org/wiki/Petroleum" title="Petroleum" >grease</a>). Citric acid is also often used in cleaning products and sodas or fizzy drinks.
Citric acid sold in a dry powdered form is commonly sold in markets and groceries as "sour salt", due to its physical resemblance to table salt. It has use in culinary applications where an acid is needed for either its chemical properties or for its sour flavor, but a dry ingredient is needed and additional flavors are unwanted (e.g., instead of vinegar or lemon juice).</p>
<h3 >[<a href="http://en.wikipedia.org/w/index.php?title=Citric_acid&action=edit§ion=10" title="Edit section: Cleaning and chelating agent" >edit</a>]Cleaning and chelating agent</h3>
<p >Citric acid is an excellent <a href="http://en.wikipedia.org/wiki/Chelation" title="Chelation" >chelating agent</a>, binding metals. It is used to remove <a href="http://en.wikipedia.org/wiki/Limescale" title="Limescale" >scale</a> from boilers and evaporators.<sup id="cite_ref-ullmann_4-3" class="reference" ><a href="http://en.wikipedia.org/wiki/Citric_acid#cite_note-ullmann-4" >[5]</a></sup> It can be used to soften water, which makes it useful in soaps and laundry <a href="http://en.wikipedia.org/wiki/Detergent" title="Detergent" >detergents</a>. By chelating the metals in <a href="http://en.wikipedia.org/wiki/Hard_water" title="Hard water" >hard water</a>, it lets these cleaners produce foam and work better without need for water softening. Citric acid is the active ingredient in some bathroom and kitchen cleaning solutions. A solution with a 6% concentration of citric acid will remove hard water stains from glass without scrubbing. In industry, it is used to dissolve rust from steel. Citric acid can be used in <a href="http://en.wikipedia.org/wiki/Shampoo" title="Shampoo" >shampoo</a> to wash out wax and coloring from the hair.</p>
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<h3 >Heavy metal detoxification</h3>
<div class="rellink relarticle mainarticle" >Main article: <a href="http://en.wikipedia.org/wiki/Chelation_therapy" title="Chelation therapy" >Chelation therapy</a></div>
<p >Chelation therapy is the use of chelating agents to detoxify <a href="http://en.wikipedia.org/wiki/Poison" title="Poison" >poisonous</a> metal agents such as <a href="http://en.wikipedia.org/wiki/Mercury_poisoning" title="Mercury poisoning" >mercury</a>, <a href="http://en.wikipedia.org/wiki/Arsenic" title="Arsenic" >arsenic</a>, and <a href="http://en.wikipedia.org/wiki/Lead" title="Lead" >lead</a> by converting them to a chemically inert form that can be excreted without further interaction with the body, and was approved by the <a href="http://en.wikipedia.org/wiki/U.S._Food_and_Drug_Administration" title="U.S. Food and Drug Administration" class="mw-redirect" >U.S. Food and Drug Administration</a> in 1991. In <a href="http://en.wikipedia.org/wiki/Alternative_medicine" title="Alternative medicine" >alternative medicine</a>, chelation is used as a <a href="http://en.wikipedia.org/wiki/Autism_therapies#Chelation_therapy" title="Autism therapies" >treatment</a> for <a href="http://en.wikipedia.org/wiki/Autism" title="Autism" >autism</a>, although this practice is controversial due to the absence of scientific plausibility, lack of FDA approval, and its potentially deadly side-effects.<sup id="cite_ref-14" class="reference" ><a href="http://en.wikipedia.org/wiki/Chelating_agent#cite_note-14" >[15]</a> </sup></p>
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Although they can be beneficial in cases of heavy metal poisoning, chelating agents can also be dangerous. Use of disodium EDTA instead of calcium EDTA has resulted in fatalities due to <a href="http://en.wikipedia.org/wiki/Hypocalcemia" title="Hypocalcemia" class="mw-redirect" >hypocalcemia</a>.<sup id="cite_ref-15" class="reference" ><a href="http://en.wikipedia.org/wiki/Chelating_agent#cite_note-15" >[16]</a></sup></p>
<h3 >Other medical applications</h3>
<p ><a href="http://en.wikipedia.org/wiki/Antibiotic" title="Antibiotic" class="mw-redirect" >Antibiotic</a> <a href="http://en.wikipedia.org/wiki/Medication" title="Medication" class="mw-redirect" >drugs</a> of the <a href="http://en.wikipedia.org/wiki/Tetracycline" title="Tetracycline" >tetracycline</a> family are chelators of <a href="http://en.wikipedia.org/wiki/Calcium" title="Calcium" >Ca</a><sup >2+</sup> and <a href="http://en.wikipedia.org/wiki/Magnesium" title="Magnesium" >Mg</a><sup >2+</sup> ions.
EDTA is also used in <a href="http://en.wikipedia.org/wiki/Endodontic_therapy" title="Endodontic therapy" >root canal treatment</a> as a way to irrigate the canal. EDTA softens the dentin facilitating access to the entire canal length and to remove the smear layer formed during instrumentation.
Chelate complexes of <a href="http://en.wikipedia.org/wiki/Gadolinium" title="Gadolinium" >gadolinium</a> are often used as <a href="http://en.wikipedia.org/wiki/Contrast_medium" title="Contrast medium" >contrast agents</a> in <a href="http://en.wikipedia.org/wiki/MRI" title="MRI" class="mw-redirect" >MRI scans</a>.</p>
<h3 >Chemical applications</h3>
<p ><a href="http://en.wikipedia.org/wiki/Homogeneous_catalyst" title="Homogeneous catalyst" class="mw-redirect" >Homogeneous catalysts</a> are often chelated complexes. A typical example is the <a href="http://en.wikipedia.org/w/index.php?title=Ruthenium(II)_chloride&action=edit&redlink=1" class="new" title="Ruthenium(II) chloride (page does not exist)" >ruthenium(II) chloride</a> chelated with <a href="http://en.wikipedia.org/wiki/BINAP" title="BINAP" >BINAP</a> (a bidentate <a href="http://en.wikipedia.org/wiki/Phosphine" title="Phosphine" >phosphine</a>) used in e.g. <a href="http://en.wikipedia.org/wiki/Noyori_asymmetric_hydrogenation" title="Noyori asymmetric hydrogenation" >Noyori asymmetric hydrogenation</a> and asymmetric isomerization. The latter has the practical use of manufacture of synthetic <a href="http://en.wikipedia.org/wiki/Menthol" title="Menthol" >(–)-menthol</a>.</p>
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<a href="http://en.wikipedia.org/wiki/Citric_acid" title="Citric acid" >Citric acid</a> is used to <a href="http://en.wikipedia.org/wiki/Citric_acid#Water_softening" title="Citric acid" >soften water</a> in <a href="http://en.wikipedia.org/wiki/Soap" title="Soap" >soaps</a> and laundry <a href="http://en.wikipedia.org/wiki/Detergent" title="Detergent" >detergents</a>. A common synthetic chelator is <a href="http://en.wikipedia.org/wiki/EDTA" title="EDTA" class="mw-redirect" >EDTA</a>. <a href="http://en.wikipedia.org/wiki/Phosphonate" title="Phosphonate" >Phosphonates</a> are also well known chelating agents. Chelators are used in water treatment programs and specifically in <a href="http://en.wikipedia.org/w/index.php?title=Steam_engineering&action=edit&redlink=1" class="new" title="Steam engineering (page does not exist)" >steam engineering</a>, e.g., <a href="http://en.wikipedia.org/w/index.php?title=Boiler_water_treatment_system&action=edit&redlink=1" class="new" title="Boiler water treatment system (page does not exist)" >boiler water treatment system</a>: <i>Chelant Water Treatment system.</i>
Products such as Bio-Rust and Evapo-Rust are chelating agents sold for the removal of rust from iron and steel.</p>