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Citric Acid (C₆H₈O₇)
Citric acid (CA), also known as citric acid, has a molecular formula of C₆H₈O₇. It is an important organic weak acid. It is a colorless crystal, odorless, easily soluble in water, and its solution is acidic. In biochemistry, it is an intermediate in the citric acid cycle (tricarboxylic acid cycle), which occurs in the metabolism of all aerobic organisms. Citric acid is widely used as an acidity regulator, flavoring agent, and chelating agent.
Food Grade Citric Acid CHANGHONG
In food processing, sodium bicarbonate is the most widely used loosening agent, used in the production of biscuits, bread, etc., but sodium carbonate will remain after the action. Excessive use will cause the food alkalinity to be too high, resulting in a deterioration of flavor and a yellow-brown color. It is a generator of carbon dioxide in carbonated beverages; it can be compounded with alum to form alkaline baking powder, and it can also be compounded with soda ash to form civilian soda ash; it can also be used as a butter preservative. It can be used as a color preservative for fruits and vegetables in vegetable processing. Adding about 0.1%~0.2% of sodium bicarbonate when washing fruits and vegetables can stabilize the green color. When sodium bicarbonate is used as a fruit and vegetable treatment agent, it can increase the pH value of fruits and vegetables by boiling and bleaching fruits and vegetables, improve the water holding capacity of proteins, promote the softening of food tissue cells, and dissolve astringent components. In addition, it has a deodorizing effect on goat milk, and the usage amount is 0.001%~0.002%.
Science and Prudence
Storage Method
Keep the container sealed and store in a cool, dry place, in a cool, dry, ventilated warehouse. Do not store it together with NaOH or Ca(OH)2.
Beware of fire
In case of fire, you can spray water, spray or use dry powder, carbon dioxide, foam fire extinguishing agent to put out the fire.
Moisture-proof and rain-proof
Pay attention to moisture-proof, rain-proof and sun-proof during transportation. Prevent the package from being damaged during transportation.
Be cautious about mixed transportation
It is strictly forbidden to mix and transport with oxidants, acids, edible chemicals, etc. It should be protected from sun exposure, rain and high temperature during transportation.
Development History
Citric Acid in China
In 1784, chemist Carl Wilhelm Scheele first isolated citric acid from lemon juice and crystallized it.
In 1890, the first industrial-scale production of citric acid began on the basis of the Italian citrus fruit industry, treating the juice with slaked lime (calcium hydroxide) to precipitate calcium citrate, which was then separated and converted into citric acid with dilute sulfuric acid.
In 1917, American food chemist James Currie discovered that certain strains of Aspergillus niger could efficiently produce citric acid, and two years later, Pfizer Pharmaceuticals began using this technology for industrial production. In 1929, Citrique Belge also began production using this technology. This production technology is still the main industrial production route for citric acid. In this technology, Aspergillus niger cultures are fed on a medium containing sucrose or glucose to produce citric acid. The source of sugar is corn steep liquor, molasses, hydrolyzed corn starch or other cheap sugary solutions. After filtering the mold from the resulting solution, the citric acid is precipitated with calcium hydroxide to produce calcium citrate, from which the citric acid is regenerated by treatment with sulfuric acid, just as it is extracted directly from citrus juice.
In 1977, Lever Brothers obtained a patent for the chemical synthesis of citric acid from calcium aconitum or calcium isocitrate (also known as calcium isocitrate) under high pressure conditions. This appears to be a reverse, non-enzymatic TCA cycle reaction that produces nearly quantitative citric acid.
In 2018, global production exceeded 2 million tons. More than 50% of this was produced in China. More than 50% is used as an acidity regulator in beverages, about 20% is used in other food applications, 20% is used in detergent applications, and 10% is used in applications other than food, such as cosmetics, pharmaceuticals, and the chemical industry.
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Natural citric acid is widely distributed in nature. It exists in fruits such as lemons, oranges, pineapples, and animals’ bones, muscles, and blood. Synthetic citric acid is produced by fermenting sugar-containing substances such as sugar, molasses, starch, and grapes.
Product Details
Citric acid is a versatile precursor for many other organic compounds. Citraconic acid can be prepared by thermal isomerization of citraconic anhydride, which can be obtained by dry distillation of citric acid. Aconitic acid can be synthesized by dehydrating citric acid with sulfuric acid.
- Melting point: 153-159 oC
- Boiling point: 309.6±42.0 oC (760 mmHg)
- Vapor density: 7.26 (vs air)
- Vapor pressure: <0.1 hPa (20 oC)
- Refractive index: 1.493~1.509
- Flash point: 155.2±24.4 oC
- Solubility: soluble in water, ethanol, ether, insoluble in benzene, slightly soluble in chloroform
- PH: 3.24 (1 mM aqueous solution); 2.62 (10 mM aqueous solution); 2.08 (100 mM aqueous solution)
Other characteristics
Existence form:
Citric acid can exist in anhydrous or monohydrate form. The crystal form of citric acid varies depending on the crystallization conditions. It is slightly weathered in dry air and hygroscopic in humid air. It can be decomposed into various products by heating and can react with acids, alkalis, glycerol, etc. Anhydrous citric acid is crystallized from hot water, while monohydrate citric acid is crystallized from cold water. Monohydrate citric acid can be converted to anhydrous citric acid by removing bound water at about 78 °C. Citric acid is also soluble in anhydrous ethanol at 15 °C (76 parts of citric acid per 100 parts of ethanol) and reacts with ethanol to form ethyl citrate. At temperatures above about 175 °C, citric acid decomposes and releases carbon dioxide.
Ionization:
Citrate is a tribasic acid [5] with ionization constants at 25 °C of: pK1=3.13; pK2=4.76; pK3=6.40 [6]. In biological systems at pH around 7, the two species present are the citrate ion and the monohydrogen citrate ion.
Complexation:
The citrate ion forms complexes with metal cations. Due to chelation, the stability constants for the formation of these complexes are quite large. Thus, it can even form complexes with alkali metal cations. However, when all three carboxyl groups are used to form chelate complexes, 7- or 8-membered chelate rings are formed, which are generally less thermodynamically stable than smaller chelate rings. Therefore, the hydroxyl group can be deprotonated to form part of a more stable 5-membered ring, such as ammonium ferric citrate
Esterification:
Citrate can be esterified at one or more of its three carboxylic acid groups to form any of a variety of monoesters, diesters, triesters, and mixed esters.
Food industry
Citric acid is the world’s largest organic acid produced by biochemical methods. Citric acid and its salts are one of the mainstay products of the fermentation industry and are mainly used in the food industry, such as acidulants, solubilizers, buffers, antioxidants, deodorants, flavor enhancers, gelling agents, colorants, etc.
In terms of food additives, it is mainly used in carbonated beverages, fruit juice drinks, lactic acid drinks and other refreshing beverages and pickled products, and its demand varies with seasonal climate changes. Citric acid accounts for about 2/3 of the total consumption of acidulants. Adding citric acid to canned fruit can maintain or improve the flavor of the fruit, increase the acidity of some low-acidity fruits during canning (lowering the pH value), weaken the heat resistance of microorganisms and inhibit their growth, and prevent bacterial swelling and damage to canned fruit with low acidity. Adding citric acid as an acidulant to candy is easy to coordinate with the fruit flavor. Using citric acid in gel foods such as jams and jellies can effectively reduce the negative charge of pectin, thereby causing hydrogen bonds between pectin molecules to gel. When processing canned vegetables, some vegetables react alkaline. Using citric acid as a pH adjuster can not only play a seasoning role, but also maintain its quality. The chelation and pH adjustment properties of citric acid enable it to increase the performance of antioxidants, inhibit enzyme activity, and extend the shelf life of food in the processing of quick-frozen foods.
Metal Cleaning
Citric acid is an organic acid produced by microbial fermentation. It is widely used in detergent production. Its own specificity and chelation play a positive role. In the actual use process, citric acid has good performance, mainly in terms of safety. The raw materials for preparing citric acid are all derived from grain, which is a safe food-grade microorganism. The use of citric acid will not affect the environment. It is easy to degrade under the action of microorganisms and heat. Its own chelating ability is also relatively strong. Mainly, citrate has a strong chelating ability for manganese ions and iron ions, and the use effect is also relatively outstanding. The corrosion inhibition of citric acid in detergent is also outstanding. Acid pickling is an important step in chemical cleaning. Compared with inorganic acids, citric acid is relatively weak in acidity, so the corrosion to equipment is relatively small. Citric acid cleaning is safe and reliable, and waste liquid is easy to handle, which will not cause harm to the human body.
(1) Mechanism of citric acid cleaning
Citric acid has little corrosion to metals and is a safe cleaning agent. Since citric acid does not contain Cl-, it will not cause stress corrosion of equipment. It can complex Fe3+ and weaken the promoting effect of Fe3+ on corrosion.
Citric acid can dissolve iron oxide and copper oxide to form citric iron and copper complexes. If an ammoniated citric acid solution is used, it can form highly soluble ferrous citrate and ferric citrate complexes with excellent cleaning effects. Citric acid is mainly used to remove rust, so it is mainly used to clean newly built boilers. Citric acid mixed with aminosulfonic acid, glycolic acid or formic acid can be used to clean calcium and magnesium scale and rust in boilers. Citric acid mixed with ethylenediaminetetraacetic acid (EDTA) can be used to clean superheaters.
Citric acid and its derivatives have a wide range of uses in many fields such as chemical cleaning due to their special physical and chemical properties.
(2) Citric acid pipe cleaning
This is the latest cleaning technology for high-impurity hard water. Food-grade citric acid is used to soften stubborn scale, and then a microcomputer is used to control water flow and pneumatics to generate water flow oscillation, so that the old scale in the water pipe is peeled off and the water pipe is unblocked and clean.
(3) Cleaning gas water heaters with compound surfactants
Chemical cleaning agents prepared with citric acid, AES and benzotriazole are used to clean gas water heaters that have been used for many years. The cleaning agent is injected into the inverted water heater, soaked for 1 hour, then the cleaning liquid is poured out, rinsed with clean water, and the water heater is reused. At the same flow rate, the outlet water temperature increases by 5℃ to 8℃.
(4) Cleaning water dispensers
Dilute edible citric acid (powdered) with water, inject it into the heating tank of the water dispenser, and soak for about 20 minutes. Finally, rinse the tank repeatedly with clean water until it is clean. It is non-toxic and has good effects.
Fine chemical industry
Citric acid is a kind of fruit acid that can accelerate the renewal of cuticles. It is commonly used in lotions, creams, shampoos, whitening products, anti-aging products, acne products, etc. In chemical technology, citric acid can be used as experimental reagents, chromatographic analysis reagents and biochemical reagents; as a chelating agent, masking agent; and used to prepare buffer solutions. Using citric acid or citrates as detergents can improve the performance of washing products, quickly precipitate metal ions, prevent pollutants from reattaching to fabrics, maintain the alkalinity necessary for washing, disperse and suspend dirt and ash, improve the performance of surfactants, and is an excellent chelating agent; it can be used as a reagent to test the acid resistance of architectural ceramic tiles. Citric acid-sodium citrate buffer is used for flue gas desulfurization. Citric acid-sodium citrate buffer solution is a desulfurization absorbent with great development value due to its low vapor pressure, non-toxicity, stable chemical properties, and high absorption rate for SO2.
Citric acid can be used as a formaldehyde-free dyeing finishing agent to improve the wearing performance of fabrics or make fabrics have water-repellent and oil-repellent properties.
Citric acid esters have been approved by the US Food and Drug Administration as non-toxic plasticizers for polyvinyl chloride and cellulose plastic films used for food packaging. Acetylated and butyrylated citrates can be used as foaming agents for methyl methacrylate polymers, stabilizers for acrylamide, initiators for polyamide adhesives, plasticizers for polyvinyl chloride, etc. In particular, butyl citrate and acetylated tributyl citrate are universally recognized non-toxic plasticizers. In addition to being non-toxic, they are also more superior in terms of compatibility, extraction resistance, and low volatility. For example, acetylated trihexyl citrate and butyrylated tributyl citrate can be used to produce component blood transfusion tubes and catheters with high hygiene requirements.
Sterilization and coagulation process
Citrate combined with 80 ℃ temperature has a good effect in killing bacterial spores, and can effectively kill bacterial spores contaminated in the hemodialysis machine pipeline. Calcium ions must participate in the formation of prothrombin activators and the subsequent coagulation process. Citrate ions and calcium ions can form a soluble complex that is difficult to dissociate, thereby reducing the calcium ion concentration in the blood and hindering blood coagulation.
Animal husbandry
Citrate is formed by the carboxylation of acetyl coenzyme A and oxaloacetic acid in the body’s tricarboxylic acid cycle, and participates in the metabolism of sugar, fat and protein in the body. Natural citric acid exists in the fruits of plants (such as lemons, citrus fruits, pineapples, etc.) and in the bones, muscles, and blood of animals. Artificial synthesis is produced by fermenting sugar, molasses, starch, grapes, and other sugar-containing substances. Adding citric acid to compound feed can disinfect, prevent mildew, and prevent salmonella and other infections in animal feed. Animals eating citric acid can reduce the proliferation of pathogens and inhibit the production of toxic metabolites, thereby increasing animal stress resistance.
(1) Increase feed intake and promote nutrient digestion and absorption.
Adding citric acid to livestock diets can directly stimulate the taste buds in the mouth, increase saliva secretion, act as a seasoning, enhance animal appetite, and thus increase animal feed intake. Adding citric acid to the diet can lower the pH of the feed. After the animal eats, the acidity in the stomach increases, and the inactive pepsinogen is converted into active pepsin, or the secretion of digestive enzymes is directly stimulated. In addition, after the acidic chyme enters the small intestine, it stimulates the small intestine to secrete enterogastrone, which reflexively inhibits gastric motility, delays gastric emptying time, and increases the time for chyme to pass through the intestine, thereby promoting the digestion of nutrients.
(2) Promote the health of intestinal flora.
Organic acids can enter the cell wall of bacteria, causing pH gradient changes inside and outside the bacteria, inhibiting bacterial growth. The suitable pH for the growth of several common pathogens is neutral to alkaline. For example, the suitable pH for Escherichia coli is 6.0-8.0, and that for Streptococcus is 6.0-7.5. Probiotics such as lactic acid bacteria are suitable for reproduction in an acidic environment. Citric acid lowers the pH in the gastrointestinal tract, providing good growth conditions for probiotics such as lactic acid bacteria in the intestine, thereby maintaining the normal balance of microbial flora in the digestive tract of livestock and poultry.
(3) Enhance the body’s anti-stress and immune ability.
Immune active cells, namely T lymphocytes and B lymphocytes, play an immune surveillance role in the body. Studies have shown that feeding citric acid to broilers can increase the density of immune active cells, keep the chickens in a better immune state, inhibit the reproduction of intestinal pathogens and prevent the occurrence of infectious diseases.
(4) As an antifungal agent and antioxidant
Citric acid is a natural preservative. Since citric acid can lower the pH of the feed, the proliferation of harmful microorganisms and the production of toxins are inhibited, and it has a significant antifungal effect. As an antioxidant synergist, mixing citric acid with antioxidants can improve the antioxidant effect, prevent or delay feed oxidation, improve the stability of compound feed and extend the storage period.
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