Citric acid is an important organic acid, also known as citric acid, colorless crystals, often containing one molecule of water of crystallization, odorless, strong acidity, and soluble in water. Its calcium salt is easily dissolved in cold water than hot water, and this property is commonly used to identify and separate citric acid. Anhydrous citric acid can be obtained by controlling a suitable temperature during crystallization. It has many uses in the industrial, food, and cosmetic industries.
Product properties
Physical properties
At room temperature, citric acid is a colorless translucent crystal or white granule or white crystalline powder, odorless, very acidic, astringent, slightly corrosive, deliquescent, accompanied by water of crystallization The compound is formed and is slightly deliquescent in moist air. It may be in the form of an anhydrate or a monohydrate: when citric acid crystallizes from hot water, it forms an anhydrate; when crystallized in cold water, it forms a monohydrate. Upon heating to 78 ° C, the monohydrate will decompose to give an anhydrate. At 15 degrees Celsius, citric acid can also be dissolved in absolute ethanol.
The crystal form of citric acid varies depending on the crystallization conditions. There are anhydrous citric acid C6H8O7 and citric acid 2C6H8O7.H2O, C6H8O7.H2O or C6H8O7.2H2O containing crystal water.
Chemical Properties
Structurally citric acid is a tricarboxylic acid compound and thus has similar physical and chemical properties to other carboxylic acids. When heated to 175 ° C it will decompose to produce carbon dioxide and water, leaving some white crystals. Citric acid is a strong organic acid, and 3 H+ can be ionized; heating can be decomposed into various products and react with acids, bases, glycerol and the like.
Used in the food industry
Because citric acid has a mild and sour acidity, it is widely used in the manufacture of various beverages, sodas, wines, candies, snacks, biscuits, canned juices, dairy products and other foods. In the market of all organic acids, the citric acid market share is more than 70%, and there is currently no acidifier that can replace citric acid. One molecule of crystalline water citric acid is mainly used as an acidic flavoring agent for refreshing beverages, fruit juices, jams, fruit sugars and canned foods, and also as an antioxidant for edible oils. At the same time, it improves the sensory traits of food, enhances appetite and promotes the digestion and absorption of calcium and phosphorus substances in the body. Anhydrous citric acid is used in large quantities in solid beverages Salts of citric acid such as calcium citrate and ferric citrate are fortifiers that require the addition of calcium and iron ions in certain foods. Esters of citric acid, such as triethyl citrate, can be used as a non-toxic plasticizer to make plastic film for food packaging. It is a sour agent and preservative in the beverage and food industry.
Used in chemical and textile industries.
Citric acid can be used as a chemical analysis reagent for chemical analysis, as an experimental reagent, a chromatographic reagent and a biochemical reagent; as a complexing agent and a masking agent; The use of citric acid or citrate as a builder can improve the performance of the washing product, can quickly precipitate metal ions, prevent the re-attachment of contaminants on the fabric, maintain the necessary alkalinity for washing, and disperse and suspend the dirt and ash; It is an excellent chelating agent for improving the performance of surfactants; it can be used as an acid-resistant reagent for testing architectural ceramic tiles.
Formaldehyde pollution of clothing has become a very sensitive problem. Citric acid and modified citric acid can be made into a formaldehyde-free anti-wrinkle finishing agent for anti-wrinkle finishing of cotton fabrics. Not only is the anti-wrinkle effect good, but the cost is low.
Used in environmental protection
Citric acid-sodium citrate buffer for flue gas desulfurization. China is rich in coal resources and is a major component of energy. However, there has been a lack of effective flue gas desulfurization processes, resulting in serious atmospheric SO2 pollution. At present, China's annual SO2 emissions have reached nearly 40 million tons. It is imperative to study effective desulfurization processes. The citric acid-sodium citrate buffer solution is a developmental desulfurization absorbent because of its low vapor pressure, non-toxicity, stable chemical properties, and high SO2 absorption rate.
For poultry production
Adding citric acid to piglet feed can early weaning, increase feed utilization by 5% to 10%, and increase sow litter size. Adding 1% to 2% citric acid to the growing and finishing pig diet can increase daily gain, reduce feed to meat ratio, increase protein digestibility, reduce back fat thickness, and improve meat quality and carcass characteristics. Rare earth citrate is a new type of high-efficiency feed additive suitable for pigs, chickens, fish, shrimps, cattle, sheep, rabbits, silkworms and other animals. It promotes animal growth, improves product quality, and improves disease resistance and survival rate. Improve the feed conversion rate and shorten the feeding cycle.
Used in cosmetics
Citric acid is a kind of fruit acid. Its main function is to speed up keratin renewal. It is often used in lotion, cream, shampoo, whitening products, anti-aging products, acne products and so on. The renewal of keratin helps the exfoliation of melanin in the skin, the shrinkage of pores, the dissolution of blackheads, and the like. For example, Biotherm Springs Shumin Cleansing Moss makes skin soft and comfortable, and the skin is fresh and pure.
For sterilization, the combination of
citric acid and 80 °C temperature has a good effect of killing bacterial spores, and can effectively kill contaminated bacterial spores in the hemodialysis machine pipeline. Lemon, which enjoys the reputation of “King of Western Food”, has a strong bactericidal effect and is good for food hygiene. Coupled with the fragrant smell of lemon, people have always liked to use it to make cold dishes, which is not only delicious but also appetizing.
For medicine
In the formation of prothrombin activator and subsequent coagulation, calcium must be involved. The citrate ion and the calcium ion can form a soluble complex which is difficult to dissociate, thereby lowering the calcium ion concentration in the blood and blocking the blood coagulation. This product is used as an in vitro anticoagulant when blood transfusion or laboratory blood sample anticoagulation.
