Citric Acid is an acidulant and antioxidant produced by mold fer-
mentation of sugar solutions and by extraction from lemon juice,
lime juice, and pineapple canning residue. it is the predominant
acid in oranges, lemons, and limes. it exists in anhydrous and mono-
hydrate forms. the anhydrous form is crystallized in hot solutions
and the monohydrate form is crystallized from cold (below 36.5°c)
solutions. anhydrous citric acid has a solubility of 146 g and mono-
hydrate citric acid has a solubility of 175 g/100 ml of distilled water
at 20°c. a 1% solution has a ph of 2.3 at 25°c. it is a hygroscopic,
strong acid of tart flavor. it is used as an acidulant in fruit drinks and
carbonated beverages at 0.25–0.40%, in cheese at 3–4%, and in
jellies. it is used as an antioxidant in instant potatoes, wheat chips,
and potato sticks, where it prevents spoilage by trapping the metal
ions. it is used in combination with antioxidants in the processing
of fresh frozen fruits to prevent discoloration.
Citric acid cycle Citrate, the conjugate base of citric acid is one of a series of compounds involved in the physiological oxidation of fats, proteins, and carbohydrates to carbon dioxide and water. This series of chemical reactions is central to nearly all metabolic reactions, and is the source of two-thirds of the foodderived energy in higher organisms. Hans Adolf Krebs received the 1953 Nobel Prize in Physiology or Medicine for the discovery. The series of reactions is known by various names, including the "citric acid cycle", the "Krebs cycle" or "Szent-Gy?rgyi — Krebs cycle", and the "tricarboxylic acid (TCA) cycle". Other biological roles Citrate is a critical component of bone, helping to regulate the size of calcium crystals.
Citric acid is a weak organic acid with the formula C6H8O7. It is a natural preservative / conservative and is also used to add an acidic, or sour, taste to foods and soft drinks. In biochemistry, the conjugate base of citric acid, citrate, is important as an intermediate in the citric acid cycle, which occurs in the metabolism of all aerobic organisms. 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 chelating agent.
Citric acid is a white, crystalline, weak organic acid present in most plants and many animals
as an intermediate in cellular respiration. Citric acid contains three carboxyl groups making it
a carboxylic, more specifically a tricarboxylic, acid.the name citrus originates from the Greek
kedromelon meaning apple of melon for the fruit citron. Greek works mention kitron, kitrion,
or kitreos for citron fruit, which is an oblong fruit several inches long from the scrublike tree
Citrus medica. Lemons and limes have high citric acid content, which may account for up to
8% of the fruit’s dry weight.Citric acid is a weak acid and loses hydrogen ions from its three carboxyl groups (COOH)
in solution.the loss of a hydrogen ion from each group in the molecule results in the citrate
3?. A citric acid molecule also forms intermediate ions when one or two
hydrogen atoms in the carboxyl groups ionize.the citrate ion combines with metals to form
salts, the most common of which is calcium citrate. Citric acid forms esters to produce various
citrates, for example trimethyl citrate and triethyl citrate.
citric acid has astringent and anti-oxidant properties. It can also be used as a product stabilizer, pH adjuster, and preservative with a low sensitizing potential. It is not usually irritating to normal skin, but it can cause burning and redness when applied to chapped, cracked, or otherwise inflamed skin. It is derived from citrus fruits.
The discovery of citric acid is credited to Jabir ibn Hayyan (Latin
name Geber, 721–815). Citric acid wasfirst isolated in 1784 by the Swedish chemist Carl
Wilhelm Scheele (1742–1786), who crystallized it from lemon juice.
Commonly used laboratory reagent
Aroma threshold values
By mycological fermentation using molasses and strains of Aspergillus niger; from citrus juices and pineapple wastes
Citric acid is a weak organic acid that is known as a commodity chemical, as more than a million tonnes are produced every year by mycological fermentation on an industrial scale using crude sugar sol
utions, such as molasses and strains of Aspergillus niger. Citric acid is widely distributed in plants and in animal tissues and fluids and exist in greater than grace amounts in variety of fruits and
vegetables, most notably in citrus fruits such as lemon and limes. Citric acid is mainly used as an acidifier, flavoring agent and chelating agent.
Behavior in Fire: Melts and decomposes. The reaction is not hazardous.
By mycological fermentation using molasses and strains of Aspergillus niger; from citrus juices and pineapple wastes
Poison by intravenous
route. Moderately toxic by subcutaneous
and intraperitoneal routes. Mildly toxic byingestion. A severe eye and moderate skin
irritant. An irritating organic acid, some
allergenic properties. Combustible liquid.
Potentially explosive reaction with metal
nitrates. When heated to decomposition it
emits acrid smoke and fumes.
Air & Water Reactions
The pure material is moisture sensitive (undergoes slow hydrolysis) Water soluble.
Applications in industry
1. metal purification
Using citric acid as the base metal cleaning formula, can effectively remove the oxides formed on the surface of ferrous and non-ferrous metals, as a weak organic acid, It can cause slight damage to the surface of the metal layer. However, as a metal ion chelating agent accelerated the migration of metal oxide, the acid system in many steel padding, in order to eliminate the metal oxides rift and the erosion of high strength steel embrittlement decreases to a minimum level, by citric acid rust to replace inorganic acid.
In the boiler, heater, superheater tubes and clean the reactor and stainless steel equipment commonly used citric acid pre-washing and cleaning to remove iron, copper oxide, especially where chloride is not permitted. Citric acid solution purification reaction is higher than that under the condition of 37.8℃, below 37.8℃ purification time should be extended accordingly. By the estimated precipitation increase or decrease in the amount to adjust the dosage of citric acid and changing conditions.
Citric acid is an efficient chelating cleaning agent, the calcium, magnesium, iron, chromium, copper and other dirt effective, widely used for a variety of metal surface cleaning, washing wastewater can be biodegradable non polluting environment.
In recent years, citric acid is applicable to metal purification of chemical processing, and is suitable for the waste solvent without pollution of podzolization, in ash molecular burning of citric acid into CO2 and water vapor and valuable metals can be recovered from the ash for toxic or radioactive elements can be closed for chemical treatment.
Sodium citrate could increase decontamination performance. In many household detergent products may be accelerating biodegradation, which can be used as a substitute for phosphate, a large number of applications in detergent, cleaning agent, citric acid and sodium aluminum silicate together with an enhancement of detergent cleaning is very effective. This kind of products use industrial grade of 50% citric acid solution as raw materials. In the synthesis of non detergent solution, because citric acid buffer action and chelated trace metal ability, hence also for hot water extraction of the carpet cleaner, bubble bath and textile softener.
3. non soil cultivation
In foreign countries use trace element nutrient liquid for plant soilless culture, which has been very common, at home also began development. In order to remove some copper in soil, excess zinc, manganese, chromium and other elements, the general use of citric acid chelate such elements. Using citric acid instead of phosphate can achieve satisfactory effect on increasing yield.
4. Application of minerals and pigments
Citric acid has distributed performance, it can reduce the viscosity of some important slurry raw material. In mining areas such as phosphate rock powder in hydraulic transport viscous problems often become the main reason for the expansion of clay, the citric acid treatment can control the expansion, the raw slurry is easy to transport. Citric acid can also reduce the precipitation concentrated raw material from titanium dioxide the ease of handling and to the overall form of transport. Citric acid can also be used for low Pulp Sizing, paint and textile raw materials processing and TiO2 dispersions.
Methods of production
Citric acid is from citric, extraction of orange and other fruits, but also use oxaloacetate and vinyl ketone as raw material of synthetic method, but at home and abroad at the present time, the industrial production methods are fermentation. Fermentation has solid state fermentation, shallow tray fermentation and submerged fermentation process. In China, more than 80% of citric acid are in sweet potato powder as raw material, submerged fermentation of Aspergillus niger, calcium carbonate and sulfate acid solution, purification, concentration, crystallization and drying .
(1) the fermentation of potato powder was put into 22%~18% of the slurry, the feed has been steam sterilization (0.2MPa, 40~60min) of the fermentation tank. Steam heated to 110℃sterilization 20min and 0.05% of the amylase of liquefaction treatment. Cooling to 35℃after inoculation of Aspergillus fermentation. Fermentation temperature prophase 36~38 C late 34~36 ℃; ventilation rate is 1: (0.1~0.2); pH value is no less than 2.5; fermentation period is for 96h. Producing acid level is 10%~14%, transforming rate is 95%.
(2) After the end of fermentation, it will be heated to 80℃in order to eliminate the mold, and then sends the plate and frame filter press to clear liquid. Filtrate to 80 ℃, adding calcium carbonate powder and neutralized to pH value is 5.0~5.5, and insulation for 0.5h. Then vacuum filtering, with 80℃ hot water washing of calcium citrate.
(3) acid solution, refined under continuous stirring, citric acid calcium was added water or dilute acid, then slowly adding sulphuric acid until the pH value is 1.8, heated to 90℃ and double end-point. Then add 1 to 3% of citric acid activated carbon, insulation for 0.5h, put a ceiling filter barrel drain, and 90℃hot water washing acid to residual acid 0.5% the following, washing with water (i.e. dilute acid) for the next acid solution by. Finally with 732 cation exchange resin by ion exchange to remove a variety of cations.
(4)concentration and crystallization, dry by ion exchange liquid contains about citric acid 15%~20% in 55~60℃: vacuum concentrated to a relative density is 1.335 to 1.340, crystallization pot. With frozen brine cooling to 36.6 ℃ precipitation water crystal. After separation and crystallization, with a small amount of distilled water to sulfuric acid content is below the 200 x 10 ". Finally, at 35 ℃ hot air drying finished.
Colorless, odorless crystals with an acid taste. Denser than water.
An organic acid obtained from lemon or lime. The colorless
crystals of this acid are soluble in water and alcohol but less
so in ether. It was used as a chemical restrainer particularly in
developers for the collodion process and in silver nitrate solutions
used for sensitizing salted and albumen papers.
Solubility in water
Citric acid exists in greater than trace amounts in a variety of fruits and vegetables, most notably citrus fruits. Lemons and limes have particularly high concentrations of the acid; it can constitute as much as 8 % of the dry weight of these fruits (about 47 g/L in the juices ) . The concentrations of citric acid in citrus fruits range from 0.005 mol/L for oranges and grapefruits to 0.30 mol/L in lemons and limes. Within species, these values vary depending on the cultivar and the circumstances in which the fruit was grown.
Citric acid and its citrate compounds are widely used in hundreds of applications. Globalproduction of citric acid in 2005 was 1.6 million tons, with China producing approximately40% of the world supply. In the United States, approximately 65% of citric acid use is in thefood and beverage industry. Citric acid is used as an acidulant to impart tartness, to controlpH, as a preservative and antioxidant, as a metal chelator, and to stabilize color and taste.Citrate salts can be used as mineral and metal dietary supplement; for example, calcium citrate is used as a calcium supplement.the second greatest use of citric acid is in detergents andcleaning products. Sodium citrate is used as a builder. Citric acid’s ability to chelate metalsmakes it useful as a water-softening agent, which can also assist in cleaning. Approximately10% of citric acid production is used in the pharmaceutical industry. Citric acid's largest usein pharmaceuticals is as an eff ervescent when combined with carbonates or bicarbonates suchas in Alka-Seltzer. As an eff ervescent, it improves tastes, buff ers, and improves solubility ofingredients. It is also used in pharmaceuticals to impart tartness to mask unpleasant medicinalfl avors, maintain stability, and as a buff ering agent.
Applications in the pharmaceutical industry
Effervescent is popular oral drug ingredients release system, citric acid and sodium carbonate or sodium bicarbonate solution common reaction produce large quantities of CO2 (i.e. effervescent) and sodium citrate, can quickly dissolve and enhance the ability to taste the active pharmaceutical ingredient. For example, the cathartic and painkillers increase dissolution. Citric acid syrup is fever patients with soft drinks, flavoring, cool and detoxification effect.
Citric acid is widely used in a variety of nutrient oral liquid, buffer pH is 3.5~4.5, maintaining the stability of the active ingredient, strengthen the preservative effect. Combined with citric acid and fruit flavor, give people like sweet sour taste to conceal the drugs of bitter, especially traditional Chinese medicine preparation, 0.02% of citric acid is added in the liquid ingredients, which can trace iron and copper complex formation, delaying the degradation of active ingredient. In the mouth chewing tablets by 0.1%~0.2% citric acid tablets can improve the flavor, lemon flavor.
The above information is edited by the Chemicalbook Hayan.
History of discovery
Citric acid was found in eighth Century in Iran alchemist Jaber.
In 1784, C.W. Scheler first crystallized the citric acid from the lemon juice, which was made by adding lime to the fruit juice to form a calcium citrate precipitate.
Natural citric acid in nature distribution is very wide, contained in plants such as lemon, citrus, pineapple and other fruits and animal bone, muscle, blood. Originally it is produced in the state of California in the United States, Italy and the West Indies. The yield of the Italian ranks first.
Citric acid fermentation process began in the late nineteenth Century.
In 1893, wemmel found that Penicillium is sugar as raw material to produce citric acid. However, until the first World War hindered the Italian lemon exports, the industry used microbial to produce of citric acid , which have not been put on the agenda.
In 1913, B. reported zahorski Niger can produce citric acid.
In 1916, Tom and curry used Aspergillus for test, which confirmed that most molds such as Aspergillus awamori, Aspergillus oryzae, Wen's Aspergillus, Trichoderma viride and Aspergillus Niger have citric acid producing ability, and Aspergillus niger acid producing ability is stronger. As Currie by Aspergillus niger for the tested strains, in 15% sucrose broth in the fermentation, the absorption of sugar rate is 55%.
In 1923, the United States Fieser company built the world first to Aspergillus niger shallow tray fermentation of citric acid factory. Then Belgium, Britain, Germany, the Soviet Union studies in succession successful fermentation of citric acid. In this way, relying on from citrus extract natural citric acid method replaced by gradually by fermentation method.
Before 1950, the citric acid production use fermentation. In 1952 American Meyers laboratory adopt deep fermentation method for large-scale production of citric acid. Since then, deep fermentation method is gradually established. The deep fermentation cycle is short , high yield, labor saving, small footprint, easy to realize instrument control and continuous, the manufacturing technology is still the most the main method of manufacturing. In this technology, Niger is put into a medium containing sucrose or glucose, which were cultured to produce citric acid. Carbohydrate sources include corn syrup, molasses fermentation liquid, the hydrolysate of corn flour or other cheap sugar solution. In the removal of mold after adding calcium hydroxide to the remaining solution in the reaction of citric acid, citric acid calcium precipitation, after separating and adding sulfuric acid can be obtain citric acid.
Citric acid is a colorless crystalline solid. It is soluble in water and alcohol. It is found in many plants, especially citrus fruits. The juice of unripe lemonsis a commercial source of citric acid.The reaction of calcium citrate and dilute sulfuric acid yields citric acid and calcium sulfate,which maybe separated by filtration. The food industry uses citric acid as a flavoring agent and as an antioxidant. Citric acid, formulated with propylene glycol and butylated hydroxy anisol,is used as a stabilizer for fats, greases,and tallow. Etching,textile dyeing, and printing operations use citric acid in various applications, and it is also used to adjust the pH in certain electroplating baths.
ChEBI: A tricarboxylic acid that is propane-1,2,3-tricarboxylic acid bearing a hydroxy substituent at position 2. It is an important metabolite in the pathway of all aerobic organisms.
Citric acid is an important compound in the process of converting fat, protein and sugar into carbon dioxide in physiology.
These reactions are almost all metabolic core reactivity, and provide energy for higher organisms. Hans Adolf Krebs because of finding this a series of reactions to win the 1953 Nobel Prize for physiology science or medicine prize. This a series reaction called "citric acid cycle, tricarboxylic acid cycle or Krebs cycle".
The application in the food industry
Citric acid is known as the first edible sour agent, China GB2760-1996 is requirements for allowing the use of food acidity regulator. In food industry widely used as sour agent, solubilizer, buffering agent, antioxidant, removing fishy smell removing sweetening agent, chelating agent, its specific purpose, numerous enumeration.
According to domestic and international statistics, the total consumption of the beverage industry account for 75%~80% of the total citric acid production. Citric acid juice is one of the natural ingredients, not only give the fruit flavor, but also solubilization buffer, antioxidant effect, the drink sugar, flavor, pigment and other ingredients blend of coordination, formation of harmonic taste and aroma, can increase resistance the antiseptic effect of microorganisms. Therefore, it is widely used in the preparation of various types of soft drinks such as fruit, fruit of soda acid in general 0.10%~0.25%. In charge of CO2 beverages, such as water, juice, sugar, acid, pigment, fragrance mixture, citric acid is used to adjust the pH to a certain acidity, making the product titration the acidity in 0.25%~0.40%. The pulp type beverage powder, the content of citric acid can be increased to 1.5%~5.0%. in recent years, with the urban and rural people's living standards continue to improve, all kinds of drinks demand increased greatly and can be predicted that in the future the consumption of citric acid in the beverage industry will increase dramatically.
2. jam and jelly
The role of citric acid in jams and jellies and in beverage is similar, regulating pH and to give the product sour, pH must be adjusted to the most suitable for pectin condensation of very narrow range. According to different types of the pectin, it can limit pH between 3.0 and 3.4. In the production of jam it can be improved flavor and prevent crystallization of sucrose sand defects.
Citric acid is added to the candy ,which can increase the acidity and prevent the oxidation of various components and sucrose crystallization. General sour candy contains 2% citric acid. Boiled sugar, the massecuite cooling process is to put acid and pigment, essence, joined together. Pectin candy production of citric acid can regulate sour taste and gel strength increased. Anhydrous citric acid is used for chewing gum and powder food.
4. frozen food
Citric acid has the characteristics of chelating and regulating pH, can strengthen the role of antioxidants and enzyme inactivation, can more reliably ensure the stability of frozen food.
Citric acid alone or with ascorbic acid used in combination, helping to prolong the shelf life of frozen fish and shellfish, which can make those cause fish spoilage and shellfish modification enzyme inactivation and chelated microelement. Seafood products before freezing is soak in 0.25% citric acid and 0.2% ISO ascorbic acid solution, is conducive to preservation. For preservation of fresh pork and prevent corruption also has an effect.
Citric acid also inhibited the frozen fruit color and aroma deterioration. This is also the suppression of fruit enzyme system and prevent the oxidation of trace elements. For example: 0.1%~0.3% citric acid and 0.001 to 0.002% isoascorbic acid combination is effective.
Citric acid is the intermediate product of the plants of a natural composition and physiological metabolism, is also one of the organic acids widely used in the field of food, medicine, chemical industry. It is colorless transparent or translucent crystal, or granular, particle powder, odorless, although has strong sour, but a pleasant, slightly astringent taste. In the warm air gradually disintegrate, in the humid air, it is slight deliquescence.
Citric acid has properties of polybasic acid, can produce ester, salt and amide, but cannot generate anhydride; carboxyl and hydroxyl groups and metal ions can form complexes or chelates; citric acid is strong acid, for carbon steel has strong corrosive effect, but is stainless steel without corrosive effects; in case of strong oxidant such as potassium permanganate, it can be oxidized to generate oxalic acid; and molten potassium hydroxide, this product is decomposed into oxalic acid and acetic acid; heated can be decomposed. Rat percutaneous LD50 is 975mg/kg.
(1) reaction with acid
Citric acid and fuming sulfuric acid mixed, at room temperature, which produce aconitic acid, slightly heating can generate 3-ketoglutarate. The mixture of citric acid and concentrated sulfuric acid, temperature at 40℃ into acetone and CO2, CO, etc.; when heated to 150℃ to generate aconitic acid anhydride; generate double Kang acid (diconic acid) C9H10O6 and CO heating to 200 ℃, CO2 and so on.
When the sulfate concentration is less than 94%, generating 3-ketoglutaric acid at low temperature; when the sulfate concentration is less than 60%, when heated to generate aconitic acid.
Anhydrous citric acid and 1 portions of nitric acid and 2 copies of the action of sulphuric acid form nitric acid ester C3H5 (ONO2) (COOH)3, it does not dissolve in ether, and barium and lead combine to form insoluble salts.
(2) Reaction with alkali
The citric acid is fused with K2CO3 or KOH or nitric acid to obtain oxalic acid and acetic acid or other salts.
Citric acid and sodium salt (such as NaCl) lime carbonization to yield acetone.
Citric acid is get boiling in alkaline solution to obtain acrylic acid (C3H4O2).
The conventional acid base neutralization reaction of citric acid can produce various kinds of salts.
(3) the effect of glycerol
Citric acid and glycerol mixed by dry distillation to obtain acetone, CO, CO2 and glycerol in the ether acetone acid ester.
The mixture of citric acid and glycerol are heated to 100 ℃, and generate citric acid ester of glycerol , which is substance like glass. If large amount of glycerol and heated to 170℃ to get citronella diglycerol( citrodiglycerin C12H18O11).
Citric acid and glycerin which is according to the molar ratio of 1:3 heat can be citric acid glyceride. With different molar ratio of which can obtain different properties of resinous substance, and some were gel or solid form, some do not dissolve in water, some solution in water. If tung oil or oil and stearic acid are heated to 100℃, can shrink synthetic resinous substance, it is used as paint and plastics additives or special solvent.
Distributed in nature
Citric acid is widely distributed in nature, found in plants such as lemon, orange, pineapple, currant, raspberry, Grape Juice fruit and animal bones, muscles, blood. Citric acid is synthesized with sugar, starch, molasses, grapes and other sugary material fermentation, can be divided into anhydrous and two kinds of pure hydrate. Citric acid is a colorless transparent crystal or white powder, odorless, has an attractive acidity. Translucent colorless crystals obtained from concentrated aqueous solution of heat in the anhydrous melting point is 153℃. Translucent colorless crystals obtained from water solution is a water softening, the density is 1.542.75 at about 100℃melting. One water compoment can loss water in dry air. It is a strong organic acid. It is soluble in water, ethanol and ether. Used in the manufacture of drugs, soda, candy, also used as a metal cleaning agent, mordant.
Many kinds of fruits and vegetables, especially citrus fruits contain more citric acid, especially lemon and lime--they contain a lot of citric acid, after drying, the content is up to 8% (in the juice content is about 47 g/L). In the citrus fruits, the content of citric acid is between 0.005 mol/L of orange and grape and 0.30 mol/L of lemon and lime . The content changes different from cultivars and plant growth.
Citric acid reacts with oxidizing agents, bases, reducing agents and metal nitrates . Reactions with metal nitrates are potentially explosive. Heating to the point of decomposition causes emission of acrid smoke and fumes [Lewis].
Inhalation of dust irritates nose and throat. Contact with eyes causes irritation.
Fermentation is the technology of choice for citric acid synthesis. Different bacteria
(e.g. Arthrobacter paraffinens and Bacillus licheniformis), filamentous fungi
(e.g. Aspergilus niger and Penicillium citrinum) and yeasts (e.g. Candida tropicalis
and Yarrowia lipolytica) are able to produce citric acid. Due to high
productivity and easy handling, citric acid is usually produced by fermentation
with A. niger. For example, a product concentration of 114 g.L-1 within
168 h has been reached by cultivation of A. niger GCMC 7 on cane molasses
. On the industrial scale, submerged cultivation, surface fermentation and
solid-state fermentation are used.
In general, molasses, starch hydrolyzate and starch are used as substrates.
However, there are various studies for alternative raw materials. Solid-state
fermentation of inexpensive agricultural wastes is one possibility. For
example, high yields up to 88 % have been achieved using grape pomace as
substrate. Lowering the cost of product recovery is crucial. Different methods
using precipitation, solvent extraction, adsorption, or in situ product recovery have
been described. One interesting process could be the in situ crystallization of
citric acid during fermentation to improve the economics.
CITRIC ACID, white crystalline solid, decomposes at higher temperatures, sp gr 1.542. Citric acid is soluble in H2O or alcohol and slightly soluble in ether. The compound is a tribasic acid, forming mono-, di-, and tri- series of salts and esters.