About the citric acid

Anhydrous citric acid is a natural component and an intermediate product of physiological metabolism in animals and plants, and it is also one of the most widely used organic acids in food, medicine, chemical, and other fields. It is colorless, transparent or translucent crystals, or granular or granular powder, odorless, and although it has a strong sour taste, it is pleasant and has a slightly astringent taste. Gradually weathered in warm air, slightly deliquescence in the humid air.
Lemon and lime citric acid are widely distributed in nature and are found in plants such as lemon, citrus, pineapple, gooseberry, raspberry, grape juice, and other fruits and animal bones, muscles, and blood. Artificially synthesized citric acid is produced by fermentation of sugar-containing substances such as sugar, molasses, starch, grapes, etc. It can be divided into two types: anhydrous and hydrate. Pure citric acid is a colorless transparent crystal or white powder, odorless, and has an attractive sour taste. The translucent colorless crystals obtained from the hot concentrated aqueous solution are anhydrous, with a melting point of 153°C. The translucent colorless crystal obtained from the cold water solution is a monohydrate with a density of 1.542. It softens at 75°C and melts at about 100°C. Monohydrates can lose water in dry air. It is a strong organic acid. Soluble in water, ethanol, and ether. Used in the manufacture of medicines, soft drinks, candy, etc., also used as metal cleaners, mordants, etc. Many kinds of fruits and vegetables, especially citrus fruits, contain more citric acid, especially lemons-they contain a lot of citric acids, after drying, the content can reach 8% (the content in the juice is about 47g /L). In citrus fruits, the content of citric acid is between 0.005mol/L for oranges and grapes and 0.30mol/L for lemons and limes. This content varies with the growth of different cultivars and plants.

Anhydrous citric acid is known as the first edible sour agent. In the food industry, it is widely used as a sour agent, solubilizer, buffer, antioxidant, deodorant, chelating agent, etc., and its specific uses are too numerous to enumerate.

Application in the food industry

1. Beverages According to domestic and foreign statistics, the consumption of citric acid in the beverage industry accounts for 75% to 80% of the total citric acid production. Citric acid is one of the natural components of fruit juice. It not only imparts fruit flavor, but also has the functions of solubilization, buffering, and anti-oxidation. It makes the sugar, flavor, pigment, and other ingredients in the beverage blend and coordinates to form a harmonious taste and aroma, which can increase anti-microbial properties. Anti-corrosion effect. Therefore, it is widely used in the preparation of various fruit-based soft drinks. For example, fruit-based soft drinks generally have an acid content between 0.10% and 0.25%. For beverages that are not filled with CO2, such as water, juice, sugar, acid, coloring, and flavor mixtures, citric acid is used to adjust the pH to a certain acidity, so that the product is titratable acidity is between 0.25% and 0.40%. For pulp-type solid beverage powder, the amount of citric acid added can be increased from 1.5% to 5.0%. In recent years, with the continuous improvement of the living standards of urban and rural people, the demand for various beverages has increased significantly. It can be predicted that the consumption of citric acid in the beverage industry will increase substantially in the future.
2. Jam and jelly The role of citric acid in jam and jelly is similar to that in beverages. It mainly adjusts the pH of the product and imparts sourness to the product. The pH must be adjusted to a very narrow range that is most suitable for pectin coagulation. According to the different types of pectin used, the pH can be limited to between 3.0 and 3.4. In the production of jam, it can improve the flavor and prevent the crystallization of sucrose from sand defects.
3. Candy citric acid added to the candy can increase the sourness and prevent the oxidation of various ingredients and the precipitation of sucrose crystals. Generally, sour candy can contain 2% citric acid. After the sugar is boiled, add citric acid, colorings, flavors, etc. together during the cooling process of the massecuite. In the production of pectin jelly, citric acid can adjust the acidity and enhance the gel strength. Anhydrous citric acid is used in chewing gum and powdered foods.
4. Frozen food citric acid has the characteristics of chelating and adjusting pH, which can strengthen the effect of antioxidants and inactivate enzymes and can more reliably ensure the stability of frozen foods. Citric acid alone or in combination with erythorbic acid helps to extend the shelf life of frozen fish and shellfish. It can inactivate enzymes that can cause fish spoilage and shellfish deterioration and chelate trace elements. Seafood products should generally be soaked in 0.25% citric acid and 0.2% erythorbic acid solution before freezing, which is conducive to preservation and refrigeration. It is also effective for fresh pork preservation and the prevention of corruption. Citric acid can also inhibit the deterioration of the color and aroma of frozen fruits, which is also the performance inhibiting the enzyme system in the fruit and preventing the oxidation of trace elements. For example, the combination of 0.1%～0.3% citric acid and 0.001%～0.002% erythorbic acid is effective. Application in the pharmaceutical industry Effervescence is a popular drug oral ingredient release system. Citric acid reacts with sodium carbonate or sodium bicarbonate aqueous solution to produce a large amount of CO2 (ie effervescence) and sodium citrate, which can quickly dissolve and enhance the active ingredients in the drug. Taste ability. For example, it has a solubilizing effect on laxatives and analgesics. The citric acid syrup is a refreshing drink for patients with fever, which has the effects of correcting, cooling, and detoxifying. Citric acid is commonly used in various nutritional oral liquid Chemicalbooks, etc., to buffer pH 3.5-4.5, maintain the stability of active ingredients, and enhance the effect of preservatives. Citric acid is used in combination with fruit flavors to give people a favorite taste of odorous acid to mask the bitter taste of drugs, especially in traditional Chinese medicine preparations. Adding 0.02% citric acid to liquid ingredients can form a trace of iron and copper complexes, delaying the degradation of active ingredients effect. The use of 0.1% to 0.2% citric acid in chewing tablets can improve the flavor of the tablets and give them a lemon flavor.

Application in industry

1. Metal purification The metal purification formula based on citric acid 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 metal surface layer. Metal ion chelating agents accelerate the migration of metal oxides. In many steel pickling systems, to eliminate metal oxide stress cracks and minimize the corrosion and embrittlement of high-strength steels, citric acid is used to remove rust instead of strong inorganic acids. . In boilers, heaters, superheater tubes, unclean reactors, and stainless steel equipment, citric acid is generally used to pre-wash and purify iron and copper oxides, especially where chlorides are not allowed. The purification reaction of citric acid solution should be carried out when the temperature is higher than 37.8℃, and the purification time below 37.8℃ should be extended accordingly. The amount of citric acid and the action conditions should be adjusted by the increase or decrease of the estimated precipitation. Citric acid is a high-efficiency chelating cleaning agent that is effective on calcium, magnesium, iron, chromium, copper, and other dirt. It is widely used for cleaning various metal surfaces. After washing, the wastewater can be biodegraded and does not pollute the environment. In recent years, citric acid is suitable for the chemical treatment of metal purification, and it is also suitable for the pollution-free ashing of waste solvents. The citric acid molecules in the ash are burned to CO2 and water vapor, and valuable metals can be recovered from the ash. , For toxic or radioactive elements, can be completely enclosed for chemical treatment.
2. Sodium citrate detergent can increase the decontamination performance. It can accelerate biodegradation in many household detergent products. It can be used as a substitute for phosphate and is widely used in detergents and detergents. Sodium citrate It is very effective to enhance the cleaning effect of detergent together with aluminosilicate. Industrial grade 50% citric acid solution is used as raw material for this type of product. In the non-synthetic detergent solution, because citric acid has a buffering effect and the ability to chelate trace metals, it is also used as a cleaning agent for hot water extraction of carpets, a bath, and a softener for textiles.
3. Soilless cultivation agronomy has long been very common in foreign countries using microelement plant nutrient solutions and has also begun to develop in China. To remove some excess elements such as copper, zinc, manganese, and chromium in the soil, citric acid is generally used to chelate these elements. Using citric acid instead of phosphate can achieve a satisfactory yield increase effect.
4. The application of citric acid in minerals and pigments has a dispersing effect, which can reduce the viscosity of some important slurry raw materials. In mining, the viscosity of phosphate rock powder in hydraulic transportation is often the main reason for clay expansion. The citric acid treatment can control the expansion and make the slurry raw meal easy to transport. Citric acid can also reduce the precipitation of the concentrated raw meal of titanium dioxide, making it easy to handle and transport in an integrated form. Citric acid can also be used as a dispersing agent for low-size sizing materials, paint and textile raw materials, and titanium dioxide.