Citric acid is used as a chelating agent in food and medicine, and it is also a chemical intermediate used in soda, candy and so on. , also used as metal cleaner and mordant.
Citric acid is widely distributed in the plant kingdom, such as lemon, gooseberry, raspberry and grape juice. It can be extracted from plant raw materials or made from sugar by citric acid fermentation.
Because citric acid has a stimulating effect, contact may cause eczema.
Citric acid powder can form a mixture with air, which may cause combustion in case of open flame, high heat or contact with oxidant.
Naturally distribute natural citric acid has a high content in lemon. Natural citric acid is widely distributed in nature. Natural citric acid exists in fruits such as lemons, oranges and pineapples, as well as in bones, muscles and blood of animals.
Many kinds of fruits and vegetables, especially citrus fruits, contain more citric acid, especially lemons and limes-they contain a lot of citric acid, and the content can reach 8% after drying (the content in juice is about 47g/L).
Among citrus fruits, the citric acid content of citrus and grape is between 0.005 mol/L and 0.30 mol/L of lemon and lime.
This content varies with the growth of different cultivated species and plants.
Physical Properties and Appearance of citric acid monohydrate Crystals
Citric acid is colorless translucent crystal, or white particles, or white crystalline powder, odorless, although it has a strong sour taste, it is pleasant and slightly astringent.
Weathering gradually in warm air and slightly deliquescent in humid air.
Soluble in water, ethanol and benzene, slightly soluble in chloroform, and the aqueous solution is acidic.
Calcium salt of citric acid is more soluble in cold water than in hot water, and is often used to identify and separate citric acid.
Stereomolecular structure of citric acid in crystalline form
The crystal morphology of citric acid varies with different crystallization conditions, including anhydrous citric acid C6.
H8O7, and citric acid 2C6H8O7 H2O, C6H8O7 H2O or C6H8O7 2H2O contain crystal water.
Anhydrous citric acid can be obtained by controlling proper temperature during crystallization.
Commercial citric acid is mainly anhydrous citric acid and citric acid monohydrate.
Citric acid monohydrate is a product obtained by crystallization, separation and drying from aqueous solution at low temperature (below 36.6℃), with molecular weight of 2 10. 14, crystallization water content of 8.58%, melting point of 70 ~ 75℃ and density of 1.542.
At 20℃, 100g water can dissolve 147g anhydrous gypsum.
When placed in dry air, the crystal water in the crystal lattice escapes and weathers.
When citric acid monohydrate crystal is slowly heated, it begins to lose water at 50 ~ 70℃, and the crystal softens at 70 ~ 75℃ and begins to melt.
When heated to 130℃, the crystal water is completely lost, and finally completely melted in the range of 135 ~ 152℃.
When citric acid monohydrate was heated violently, it melted at 100℃ and agglomerated into anhydrous citric acid. After continuous heating, it melted accurately at 153℃.
Citric acid monohydrate crystal is rhombohedral with large crystal.
Anhydrous citric acid is crystallized from high temperature (above 36.6℃) aqueous solution.
The critical temperature for the transformation of citric acid monohydrate into anhydrous citric acid is 36.6 0.15℃.
The molecular weight of anhydrous citric acid is 192. 14 and the melting point is 153℃.
The crystal morphology of anhydrous citric acid is monoclinic prism-bipyramid.
Chemical Properties hans adolf krebs Structurally speaking, citric acid is a tricarboxylic acid compound, so it has similar physical and chemical properties with other carboxylic acids.
When heated to175 C, it will decompose to produce carbon dioxide and water, leaving some white crystals.
Citric acid is a strong organic acid with three H's.
Can be ionized; Heating can be decomposed into many products, which react with acid, alkali and glycerol.
Citric acid is an important compound in the biochemical process of converting fat, protein and sugar into carbon dioxide.
These chemical reactions are the core reactions of almost all metabolism and the energy of higher organisms.
Hans adolf krebs won the 1953 Nobel Prize in Physiology or Medicine for discovering this series of reactions.
This series of reactions is called "citric acid cycle", "tricarboxylic acid cycle" or "Kjeldahl cycle".
Main uses Citric acid is the largest acid among organic acids. Because of its physical, chemical and derivative properties, it is the most important organic acid, which is widely used in food, medicine, daily chemical and other industries.
Widely used as sour agent for food and beverage.
It can also be used as raw materials and reagents for cosmetics, metal cleaning agents, mordants, nontoxic plasticizers and boiler scale inhibitors.
Its main salt products are sodium citrate, calcium salt and ammonium salt. Sodium citrate is an anticoagulant for blood, and ammonium ferric citrate can replenish blood.
Citric acid used in food industry is widely used in the production of sweets and drinks. Because of its mild and refreshing sour taste, citric acid is widely used in various beverages, soda, wine, candy, snacks, biscuits, canned fruit juice, products and other foods.
In all markets of organic acids, the market share of citric acid exceeds 70%.
One molecule of crystal water citric acid is mainly used as an acidic flavoring agent for refreshing drinks, fruit juice, jam, fruit candy and canned food, and can also be used as an antioxidant for edible oil.
Citric acid used in chemical industry can be used as a chemical reagent. Citric acid can be used as chemical analysis reagent, experimental reagent, chromatographic analysis reagent and biochemical reagent in chemical technology. Used as complexing agent and masking agent; Used to prepare buffer solution.
Citric acid or citrate used in textile industry can improve the performance of washing products, quickly precipitate metal ions, prevent pollutants from attaching to fabrics again, and maintain the alkalinity necessary for washing; Disperse and suspend dust and ashes; It is an excellent chelating agent to improve the performance of surfactants.
Citric acid for industrial use can be used as a reagent for chemical analysis in chemical technology. Formaldehyde pollution in clothing is a very sensitive problem. Citric acid and modified citric acid can be made into formaldehyde-free crease-resistant finishing agent for cotton fabric.
Not only the anti-wrinkle effect is good, but also the cost is low.
The environment-friendly citric acid-sodium citrate buffer was used for flue gas desulfurization.
Citric acid-sodium citrate buffer solution has low vapor pressure, non-toxicity, stable chemical properties and high SO2 absorption rate, so it is a desulfurization absorbent with great development value.
Citric acid used for livestock production in piglet feed can be weaned early, which can improve the feed utilization rate by 5% ~ 10% and increase the litter size of sows.
Adding 1% ~ 2% citric acid to the diet of growing-finishing pigs can increase daily gain, reduce feed-meat ratio, increase protein digestibility, reduce back fat thickness and improve meat quality and carcass characteristics.
Rare earth citrate is a new and efficient feed additive, which is suitable for pigs, chickens, fish, shrimp, cattle, sheep, rabbits, silkworms and other animals. It has the characteristics of promoting animal growth, improving product quality, improving disease resistance and survival rate, improving feed conversion rate and shortening feeding cycle.
Citric acid used in cosmetics is a kind of fruit acid, and its main function is to speed up keratin renewal. Commonly used in liquid, cream, shampoo, whitening products, anti-aging products, acne products and so on.
The renewal of keratin contributes to the shedding of melanin, the shrinking of pores and the dissolution of blackheads.
When used under the combined action of citric acid and 80℃ temperature, it has a good effect of killing bacterial spores and can effectively kill contaminated bacterial spores in the pipeline of hemodialysis machine.
Lemon enjoys the reputation of "king of western food", which is powerful and beneficial to food hygiene. Coupled with its fragrance, people always like to use its cold dishes, which are not only delicious and refreshing, but also stimulate appetite.
Citric acid used in medicine has the functions of contracting, strengthening capillaries and reducing their permeability. It can also improve coagulation function and platelet number, shorten coagulation time and bleeding time, and has a certain hemostatic effect.
The pharmaceutical industry is used as a medicinal cooling agent to determine blood potassium.
As a food agent, citric acid is an edible acid, which can enhance the normal metabolism in the body, and the appropriate dosage is harmless to the human body.
Adding citric acid to some foods tastes good and can stimulate appetite.
Although citric acid has no direct harm to human body, it can promote the excretion and deposition of calcium in the body. If you eat food containing citric acid for a long time, it may lead to hypocalcemia.
Children are characterized by nervous system instability, excitability and autonomic nervous disorder; Adults have hand and foot convulsions, muscle spasms, paresthesia, itching and digestive tract symptoms.
If you eat food soaked in industrial citric acid by mistake, the chemical residues in food will damage the nervous system, induce allergic diseases and even cause cancer.
There is little citric acid in drinks or foods, which is basically harmless to human body.
A Brief History of Production The discovery of citric acid in Jabir Ibn Khayan began with the Iranian alchemist Jaber in the 8th century.
In 1784, C.W. Scheler crystallized and separated citric acid from lemon juice for the first time.
1890, the Italian lemon juice factory opened the citric acid industry.
1893, C. Wehmer discovered that Penicillium can use sugar as raw material of citric acid.
19 17 years, American food chemist James Currie found that some types of Aspergillus Niger can citric acid efficiently.
Two years later, Pfizer began to produce citric acid using this technology.
1923, Fizer Company of the United States built the world's first factory for producing citric acid by shallow dish fermentation of Aspergillus Niger.
Before 1950, citric acid was produced by shallow dish fermentation.
1952, the American Myers Laboratory produced citric acid on a large scale by submerged fermentation.
Since then, liquid submerged fermentation has been gradually established.
Submerged fermentation has the advantages of short cycle, high yield, labor saving, small floor space, easy to realize instrument control and continuity, and has become the main method of citric acid production.
Citric acid was developed in China in 1942, and Tang Tenghan's fermentation of citric acid was the earliest record in China.
From 65438 to 0952, Cynthia and others began to ferment citric acid with Aspergillus Niger in a shallow dish.
During the period of 1966, Tianjin Institute of Industrial Microbiology and Shanghai Institute of Industrial Microbiology successively carried out experimental research on submerged fermentation of citric acid by dry potato powder of Aspergillus Niger, and achieved success, thus determining the main technical route of citric acid production in China.
Submerged fermentation of citric acid by potato dry powder is a unique advanced technology in China, with rich raw materials, simple process, no need of nutrients and high yield.
1970, Candida lipolytica was used in research institutes in Tianjin, Shanghai, Shenyang and Changzhou.
Lipolytic yeast) is used to ferment paraffin oil (n-alkanes) to produce citric acid.
1979, Xu Ziyuan and others screened a mutant strain of Candida lipolytica sensitive to fluoroacetic acid. The activity of aconitic acid hydratase is very low, and the yield of citric acid is increased from 50% to 80%, thus increasing the yield of citric acid in petroleum fermentation.
Production method of citric acid fermentation process
Citric acid production technology is divided into three methods: fruit extraction method, chemical method and biological fermentation method.
Citric acid is extracted from lemon, orange, apple and other fruits with high citric acid content.
This method has high cost and is not conducive to industrial production.
Chemical method This method is based on the chemistry of dichloro or ketene.
This method has complex process, high cost and low safety.
Aspergillus Niger produces citric acid by biological fermentation in a culture medium containing sucrose or glucose.
The sources of sugar include corn syrup, molasses fermentation broth, corn meal hydrolysate or other cheap sugar solutions.
After demoulding, calcium hydroxide is added into the remaining solution to make citric acid react to generate calcium citrate precipitate, and sulfuric acid is added after separating the precipitate to obtain citric acid.
National Standard Basic Information StandardNo. StandardNo.: GB/ T8269-2006 Chinese Standard Title In China: Citric Acid English Standard Name: Citric Acid Release Date: 2006-7- 18 Implementation Date: 2006-12-1First Issue Date. :1987-10-19 standard status: current review confirmation date: plan number: 2003 1594-T-607 instead of national standard number: GB/ T8269- 1 998 replaced by national standard number. Replacement standard: date of abolition: adopting international standard number: BP-98, USP-27 adopting international standard name: British Pharmacopoeia, USP applicability: NEQ adopting international standard: international standard classification number of foreign advanced standards (ICS): 67.220. 10 China standard classification number (CCS). Price (Yuan): Governor of the competent department: Technical Committee of the National Standardization Administration Committee: Member of the National Food Industry Standardization Technical Committee: Anhui Fengyuan Biochemical Company, Shandong Rizhao Taishan Jiejing Biochemical Company, Jiangsu Yixing Xielian Biochemical Company and China Food Fermentation Industry Research Institute. This standard specifies the chemical name, molecular formula, structural formula and relative molecular weight, product classification, requirements, analytical methods, inspection rules, marks, packaging, transportation and storage of citric acid.
This standard applies to citric acid products fermented with starch or sugar as raw materials.
By referring to this standard, the clauses in the following documents become the clauses of this standard.
All subsequent modifications (excluding errata) or revisions of dated reference documents are not applicable to this standard. However, parties who have reached an agreement according to this standard are encouraged to study whether the latest versions of these documents can be applied.
For undated reference documents, the latest edition is applicable to this standard.
GB/T 19 1 graphic signs for packaging, storage and transportation (GB/T 19 1-2000, Eqviso780:1997) GB/t601GB/t602 Standard solution for impurity determination of chemical reagents GB/T603 GB/ t606 General method for moisture determination of chemical reagents GB/ T500 must build environmental protection facilities suitable for production scale, and the discharge of main pollutants must meet the national emission standards. Enterprises that fail to meet the standards shall be stopped or limited in production according to relevant environmental protection laws and punished.
Citric acid industry implements relevant standards in Integrated Wastewater Discharge Standard and Integrated Air Pollution Discharge Standard.
According to the actual situation, the main pollutants discharged by enterprises (that is, COD in water, soot and sulfur dioxide in waste gas) are required to meet the national emission standards.
After anaerobic treatment, high-concentration citric acid wastewater and low-concentration organic wastewater are mixed into the contact oxidation tank and then into the air flotation system. The final effluent COD should meet the secondary standard of fermentation industry in newly expanded enterprises (COD≤300mg/L, SS≤200mg/L, pH = 6 ~ 9).