Citric acid is used as a multivalent chelating agent in food and medicine, and as a chemical intermediate for sodas, candies, etc. It is also used as a metal cleaner and mordant.
Citric acid is widely distributed in the plant kingdom, such as in lemons, currants, raspberries, grape juice, etc. It can be extracted from plant raw materials, and can also be produced by citric acid fermentation of sugar.
Because citric acid is an irritant, it may cause eczema in exposed individuals.
Citric acid powder and air can form sexual mixtures, in the case of open fire, high heat or contact with oxidizing agents, there is a risk of causing combustion.
Natural distribution of natural citric acid in lemons with high content of natural citric acid is widely distributed in nature, natural citric acid exists in plants such as lemons, citrus, pineapple and other fruits and animal bones, muscles, blood.
Many kinds of fruits and vegetables, especially citrus fruits contain high levels of citric acid, especially lemons and limes - they contain high levels of citric acid, up to 8% after drying (about 47 g/L in fruit juice).
In citrus fruits, the amount of citric acid ranges between 0.005 mol/L in oranges and grapes and 0.30 mol/L in lemons and limes.
This content varies with different cultivars and plant growth.
Physical PropertiesAppearanceCitric acid monohydrate crystals
Citric acid is colorless translucent crystals, or white granules, or white crystalline powder, odorless, pleasant though strongly acidic, with a slight aftertaste.
It is gradually weathered in warm air and slightly deliquescent in moist air.
Solubility soluble in water, ethanol,, insoluble in benzene, slightly soluble in chloroform, aqueous solution is acidic.
Citric acid and its calcium salt in cold water than hot water is easy to dissolve, this property is often used to identify and separate citric acid.
Crystalline form of citric acid stereo molecular structure
Citric acid crystallization form due to different crystallization conditions, there are anhydrous citric acid C6
H8O7, there are citric acid containing crystalline water 2C6H8O7-H2O, C6H8O7-H2O or C6H8O7-2H2O.
Citric acid crystallization control of suitable temperature can be obtained Anhydrous citric acid.
The commercial citric acid is mainly anhydrous citric acid and citric acid monohydrate.
Citric acid monohydrate is precipitated by crystallization from aqueous solution at low temperature (below 36.6°C), and the product after separation and drying, with a molecular weight of 210.14, containing 8.58% of crystalline water, a melting point of 70-75°C, and a density of = 1.542.
At 20°C, 147g of anhydrous material can be dissolved in 100g of water.
When placed in dry air, the The water of crystallization in the crystal lattice escapes and weathering occurs.
Citric acid monohydrate crystals slowly heated, first in 50 ~ 70 ℃ began to lose water, 70 ~ 75 ℃ crystal softening, began to melt.
Heated to 130 ° C when the complete loss of water of crystallization, and finally in the range of 135 ~ 152 ° C completely melted.
Citric acid monohydrate when heated vigorously, melting at 100 ° C, agglomeration into anhydrous citric acid, continue to heat very accurately at 153 ° C melting.
Citric acid monohydrate crystals are rhombohedral prismatic crystals with large crystals.
Anhydrous citric acid is precipitated by crystallization from an aqueous solution at high temperature (above 36.6°C).
The critical temperature for the transformation of citric acid monohydrate into anhydrous citric acid is 36.6±0.15℃.
Citric acid anhydrous has a molecular weight of 192.14 and a melting point of 153°C. It is a mixture of citric acid and citric acid anhydrous.
The crystal form of anhydrous citric acid is prismatic-diamond cone of monoclinic crystal system.
Chemical PropertiesHans Adolf KrebsStructurally citric acid is a tricarboxylic acid and as such has similar physical and chemical properties to other carboxylic acids.
When heated to 175°C it decomposes to produce carbon dioxide and water, leaving some white crystals.
Citric acid is a strong organic acid with 3 H
Ionizable; it can be decomposed by heating into a variety of products that react with acids, bases, and glycerol.
Citric acid is an important compound in the biochemical conversion of fats, proteins, and sugars to carbon dioxide.
These chemical reactions are central to almost all metabolism and energize higher organisms.
Hans Adolf Krebs won the 1953 Nobel Prize in Physiology or Medicine for his discovery of this series of reactions.
The series of reactions is called the "citric acid cycle," the "tricarboxylic acid cycle," or the "Krebs cycle.
The main use of citric acid is the first of the organic acids, due to the physical properties, chemical properties, and the performance of derivatives, it is widely used in food, medicine, cosmetics and other industries the most important organic acids.
Widely used as food, beverage acidifier and agent.
It can also be used as raw material and agent of cosmetics, metal cleaner, mordant, non-toxic plasticizer and boiler anti-scaling agent.
The main salt products are sodium citrate, calcium and ammonium salts, etc. Sodium citrate is an anticoagulant for blood, ferric ammonium citrate can be used as a blood tonic.
Used in the food industry citric acid is commonly used in the production of confectionery and beverages because citric acid has a mild and refreshing acidic flavor, and is commonly used in a variety of beverages, sodas, wines, candies, confectionery, cookies, canned juices, products, and other food products.
Citric acid has more than 70% market share among all organic acids.
A molecule of crystalline water citric acid is mainly used as an acidic flavoring agent for refreshing drinks, fruit juices, jams, fruit candies and canned goods, etc., and can also be used as an antioxidant for edible oils
Used in chemical industryCitric acid used as a chemical reagentCitric acid can be used as a chemical reagent for chemical analysis in chemical technology and used as a reagent for experimental reagents, reagents for chromatography analysis and biochemical reagents; it is used as a complexing agent, a masking agent; and it is used in the formulation of buffer solution.
Used in the textile industry using citric acid or citric acid salts as a detergent, can improve the performance of washing products, can quickly and precipitate metal ions, to prevent pollutants from re-attachment of the fabric, to maintain the washing of the necessary alkalinity; so that dirt and ash dispersion and suspension; to improve the performance of the surfactant, is an excellent chelating agent.
Industrial citric acid, in chemical technology, can be used as a reagent for chemical analysis, formaldehyde contamination of clothing has been a very sensitive issue, citric acid and modified citric acid can be made into a non-formaldehyde wrinkle-free finishing agent for wrinkle-free finishing of cotton fabrics.
Not only good wrinkle effect, and low cost.
For environmental protection citric acid - sodium citrate buffer solution for flue gas desulfurization.
Citric acid-sodium citrate buffer solution is a desulfurization absorber of great development value due to its low vapor pressure, non-toxic, chemically stable, SO2 absorption rate and other reasons.
Used in livestock production in the piglet feed citric acid, can be weaned earlier, improve feed utilization rate of 5% to 10%, increase sow litter size.
In the growth of fattening pig diet 1% ~ 2% citric acid, can increase daily weight gain, reduce the feed-to-meat ratio, improve protein digestibility, reduce the thickness of back fat, improve meat quality and carcass characteristics.
Rare earth citrate is a new type of high efficient feed agent for pigs, chickens, fish, shrimp, cattle, sheep, rabbits, silkworms and other animals, with the promotion of animal growth, improve product quality, improve disease resistance and survival rate, improve the feed conversion rate, shorten the feeding cycle and other characteristics.
Used in cosmetics citric acid belongs to a kind of fruit acid, the main role is to accelerate the renewal of keratin, commonly used in liquid, cream, shampoo, whitening products, anti-aging products, acne products.
The renewal of keratin helps the skin to peel off melanin, the pores to be thinned, and the blackheads to be dissolved.
For citric acid and 80 ℃ temperature joint action has a good role in killing bacterial spores, and can be effective in killing hemodialysis machine pipeline contamination of bacterial spores.
Lemon enjoys the reputation of "the king of Western food" has a strong role in food hygiene is very good, coupled with the lemon's fragrant odor, people traditionally like to use its gazpacho, not only tasty and refreshing, but also to enhance appetite.
Used in medicine citric acid has a contraction, solidification of capillaries and reduce their permeability, but also improve blood clotting function and the number of platelets, shorten the coagulation time and bleeding time, with a certain degree of hemostatic effect.
Pharmaceutical industry used as medicine coolant, blood potassium measurement.
Consumption note as a food agent citric acid for food acids, can enhance the body's normal metabolism, the appropriate dose is harmless to the human body.
In some food add citric acid taste good, and can promote appetite.
While citric acid is not directly harmful to the human body, it can promote the excretion and deposition of calcium in the body, such as long-term consumption of citric acid-containing foods, may lead to hypocalcemia.
Children exhibit neurological instability, excitability, and vegetative nerve disorders; adults suffer from twitching of the hands and feet, muscle spasms, sensory abnormalities, itching, and digestive tract symptoms.
If you accidentally eat industrial citric acid-soaked food, the chemical residue in the food will damage the nervous system, induce allergic diseases, and even cause cancer.
The edible citric acid contained in beverages or food is very small and basically harmless to the human body.
Brief history of productionWorld production historyJabir Ibn HayanThe discovery of citric acid began in the 8th century with the Iranian alchemist Jabir.
Citric acid was first crystallized and isolated from lemon juice by C.W. Scherer in 1784.
In 1890, Italian lemon juice factories started the citric acid industry.
In 1893, C. Weimer discovered that Penicillium can make citric acid from sugar.
In 1917, American food chemist James Currie discovered that certain types of Aspergillus niger could citric acid efficiently.
Two years later, Pfizer used this technology to begin citric acid.
In 1923 the U.S. Fraser Company constructed the world's first plant to produce citric acid by the Aspergillus niger shallow plate fermentation method.
Before 1950, citric acid was produced by shallow disk fermentation.
In 1952, the Myers Laboratory in the United States adopted the deep fermentation method to produce citric acid on a large scale.
Since then, the deep fermentation method has been gradually established.
Deep fermentation has become the main method of citric acid production because of its short cycle, high yield, labor-saving, small floor space, and ease of instrumentation control and continuity.
China's development of citric acid in 1942, Tang Teng Han citric acid by fermentation is the earliest record for China.
In 1952, Chen Sheng and others began to use Aspergillus niger shallow fermentation of citric acid.
In 1966, the Tianjin Institute of Industrial Microbiology and Shanghai Institute of Industrial Microbiology carried out experimental research on deep fermentation of citric acid by Aspergillus niger with raw materials of dried potato flour one after another, and succeeded, thus determining this main process route of citric acid production in China.
Deep fermentation of citric acid from dried potato flour is a unique and advanced process in China, with abundant raw materials, simple process, no nutritive salt and high yield.
In 1970, research units in Tianjin, Shanghai, Shenyang, Changzhou and other places carried out experiments on the production of citric acid by fermentation of paraffin oil (n-alkanes) using defatted pseudo-saccharomyces cerevisiae (candida
lipolytica).
In 1979, Xu Ziyuan et al. screened a mutant strain of Pseudohyphaea destructoriae sensitive to fluoroacetic acid, whose aconitic acid hydratase activity was very low, and the production ratio of citric acid was increased from the original 50% to 80%, which improved the yield of citric acid from oil fermentation.
Production methods citric acid fermentation process
Citric acid production process is divided into fruit extraction method, chemical method and biological fermentation method three.
Fruit extraction method citric acid is extracted from fruits with high citric acid content such as lemons, oranges and apples.
This method of extraction is more costly and not conducive to industrial production.
Chemical method of this method is based on, dichloride or vinyl ketone of the raw material of the chemical.
This method is complex, high cost and low safety.
Biofermentation method Aspergillus niger is cultured in a medium containing sucrose or glucose to produce citric acid.
Sources of sugar include corn syrup, molasses fermentation broth, hydrolyzed products of corn meal, or other inexpensive sugar solutions.
After the mold is removed, calcium hydroxide is added to the remaining solution to react the citric acid to produce a calcium citrate precipitate, and citric acid is obtained by adding sulfuric acid after the precipitate is separated.
National standard basic information StandardNo：GB/T8269-2006中文标准名称StandardTitleinChinese：Citricacid英文标准名称：Citricacid发布日期IssuanceDate：2006-7-18实施日期 ExecuteDate：2006-12-1FirstIssuanceDate：1987-10-19StandardState：CurrentReviewAffirmationDate：ReviewAffirmationDate：PlanNo：20031594-T-607 Replaced ReplacedStandard：GB/T8269-1998被取代国标号 ReplacedStandard:废止时间 RevocatoryDate：采用国际标准号 AdoptedInternationalStandardNo：BP-98,USP-27采标名称 AdoptedInternationalStandardName：British Pharmacopoeia, U.S. Pharmacopoeia AdoptedDegree：NEQ Adopted International Standard AdoptedInternationalStandard：Adopted International Standard International Standard Classification Number (ICS)：67.220.10 Chinese Standard Classification Number (CCS): X69 Standard Category StandardSort: Product Standard Page NumberofPages: Standard Price (yuan) Price (￥): The competent authorityGovernor: Standardization Administration of the National Commission of the focal point unitTechnicalCommittees: National Food Industry Standardization Technical Committee DraftingCommittee:Anhui Feng Yuan Biochemical Company, Shandong Rizhao Taishan Jiejing Biochemical Company, Jiangsu Yixing Xielian Biochemical Company, China Food Fermentation Industry Research Institute Scope This standard specifies the chemical name of citric acid, molecular formula, structural formula and relative molecular mass, product classification, requirements, analytical methods, test rules, signs, packaging, transportation and storage.
This standard applies to citric acid products produced by fermentation of starch or sugary raw materials.
Normative references to the following documents the provisions of the following documents by reference to this standard and become the provisions of this standard.
Where the cited documents are dated, all subsequent change orders (excluding errata) or revisions thereof are not applicable to this standard, however, the parties to an agreement based on this standard are encouraged to study the applicability of the most recent versions of these documents.
Any undated cited document, its latest version applies to this standard.
GB/T191 Packaging, storage and transportation of graphic symbols (GB/T191-2000,eqvISO780:1997) GB/T601 chemical reagent titration solution GB/T602 chemical reagent impurity determination of the standard solution GB/T603 chemical reagents used in the test methods of preparations and products GB/T606 general method of determination of moisture in the chemical reagent Carl Fischer Method GB/T5009 Fischer Method GB/T5009.11-2003 Determination of total arsenic and inorganic arsenic in food GB/T6682-1992 analytical laboratory water specifications and test methods (neqISO3696: 1987) GB/T50073-2001 clean plant design specifications for environmental measures wherever engaged in the production of citric acid in China's territory must be constructed to match the scale of production of environmental management facilities. All enterprises engaged in the production of citric acid in China must build environmental protection treatment facilities appropriate to the scale of production, and the main pollutant emissions must meet the national emission standards, and the enterprises that do not meet the standards will be punished in accordance with the relevant environmental laws for the suspension or restriction of production and treatment.
Citric acid industry to implement the "Comprehensive Emission Standards for Sewage" and "Comprehensive Emission Standards for Air Pollution" in the relevant standards.
Depending on the actual situation, enterprises are required to discharge major pollutants (i.e., COD in water and soot and sulfur dioxide in exhaust gas) to meet the national emission standards.
High concentration citric acid wastewater after anaerobic treatment, mixed with low concentration of organic wastewater into the contact oxidation tank, and then into the air flotation system, the final effluent COD to meet the "Comprehensive Wastewater Emission Standards" in the new expansion of the fermentation industry in the enterprise second level standards (COD ≤ 300mg / L, SS ≤ 200mg / L, pH = 6 ~ 9).