Phosphate, a salt of phosphoric acid, is one of the natural ingredients of almost all foods. As an important food ingredient and functional additive, it is widely used in food processing.
Chinese name
phosphate
Foreign name
phosphorous salts
Purpose
Important food ingredients and functional additives
Phosphate is one of the natural ingredients of almost all foods. As an important food ingredient and functional additive, it is widely used in food processing.
The naturally occurring phosphate isPhosphate rock(containing calcium phosphate), react with phosphate ore with sulfuric acid to produceCalcium dihydrogen phosphateandcalcium sulfateAnd phosphate can be prepared.Phosphate can be divided into orthophosphate and polycondensation phosphate: the phosphate used in food processing is usually sodium salt, calcium salt, potassium salt, and iron salt and zinc salt as nutrition enhancers. There are more than 30 kinds of food grade phosphate commonly used. Sodium phosphate is the main consumption type of domestic food phosphate. With the development of food processing technology,The consumption of potassium phosphate is also increasing year by year.[1]
classification
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Phosphates can be divided intoOrthophosphateAnd polyphosphates.
Orthophosphate
Orthophosphate is a ternary acid, and there are three types of orthophosphates:
1. Dihydrogen phosphate MHtwoPOfour, also known as a generation of phosphate, are soluble in water;
2. Hydrogen phosphate MtwoHPO4，Also called second generation phosphate;
3. Orthophosphate MthreePOfour, also called third-generation phosphate.
The latter two are generally insoluble in water except sodium, potassium and ammonium salts.M can be a metal of other valence states besides univalent metal.Sodium dihydrogen phosphate is used to control the concentration of hydrogen ion in the solution;Disodium hydrogen phosphate is used for water treatment as a precipitant for multivalent metals;Trisodium phosphate is used to make soaps and detergents.
Pyrophosphate
Pyrophosphoric acid is a quaternary acid. There are four kinds of pyrophosphates, of which MtwoHtwoPtwoOsevenAnd MfourPtwoOsevenType A is common.
Metaphosphate
Metaphosphate is usually a compound polymerized into a ring, and the general formula is (MPOthree)nThe common ones are dimeric metaphosphate (six membered ring) and tetrameric metaphosphate (eight membered ring). Polymetaphosphate has no definite crystal structure, which is also called phosphate glass.Sodium hexametaphosphate is the most common phosphate vitreous body. It has no fixed melting point, and its solubility in water is uncertain. The pH of the aqueous solution is between 5.5 and 6.4. In fact, one has 20 to 100 POthreeLong chain compound of the unit.Chain phosphate can be used as treatment agent, pigment dispersant, slurry dispersant and metal preservative for boiler water.
Phosphate ion can generate characteristic yellow ammonium phosphomolybdate precipitation, which can be used for analysis and verification.[1]
Physical and chemical properties
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The structural formula of phosphoric acid functional group in acid solution.In alkaline solution, the functional group will release two hydrogen atoms and ionize the phosphate with a formal charge of - 2.Phosphate ion is a polyatomic ion, which contains one phosphorus atom and is surrounded by four oxygen atoms to form a regular tetrahedron.The phosphate ion has a formal charge of - 3 and is a conjugated base of the hydrogen phosphate ion;The hydrogen phosphate ion is the conjugated base of the dihydrogen phosphate ion;The dihydrogen phosphate ion is a conjugated base of phosphoric acid.It is a hypervalent molecule (the phosphorus atom has 10 electrons in its valence shell).Phosphate is also an organic phosphorus compound, and its chemical formula is OP (OR)three。
Except for some alkali metals, most phosphates are insoluble in water under standard conditions.
In dilute aqueous solution, phosphate exists in four forms.In strong alkaline environment, there will be more phosphate ions;In weak alkaline environment, there are more hydrogen phosphate ions.In weak acid environment, dihydrogen phosphate ion is more common;In strong acid environment, water-soluble phosphoric acid is the main form.[1]
Main forms
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Structural formula of phosphoric acid functional group in acid solution
Phosphate is a naturally occurring form of elemental phosphorus, which can be found in a variety of phosphate minerals.Phosphorus or phosphide of elements is difficult to find (only a small amount can be found in meteorites).In mineralogy and geology, phosphate refers to rocks or ores containing phosphate ions.
The largest type of phosphate rock deposit in North America is located in the central Florida of the United States, the Sodas Springs in Idaho, and the coastal area of North Carolina.The second is located in Montana, Tennessee, Georgia and South Carolina near Charleston.Nauru, a small island country, used to have a large number of high-quality phosphate minerals, but now it has been extensively excavated.Phosphate rock powder can also be found in Navassa, Morocco, Tunisia, Israel, Togo and Jordan, where there are also a large number of phosphate mines.
In biology, phosphorus appears in the form of free phosphate ions in solution, called "inorganic phosphate", which is different from other phosphates in phosphate esters.Inorganic phosphate is expressed in Pi, which can be obtained by hydrolysis of pyrophosphate (expressed in PPi).
However, the most common phosphate isAdenosine monophosphate（AMP）、Adenosine diphosphate（ADP）、Adenosine triphosphate（ATP）、Deoxyribonucleic acid(DNA) andRibonucleic acid(RNA) and can be released by hydrolysis of ADP or ATP.Similar reactions were also observed for other diphosphate or triphosphate nucleosides.The phosphoric anhydride bond in ADP and ATP, or other diphosphate and triphosphate nucleosides, contains a lot of energy, so they play an important role in biology.They are generally called high-energy phosphate, just like creatine phosphate in muscle tissue.Some compounds such as phosphine can also be used in organic chemistry, but it seems that there is no natural equivalent.
Because of the importance of phosphate to biology, it is highly collected ecologically.Therefore, it is often a limited reagent in the environment, and its availability determines the speed of biological growth.Adding a large amount of phosphate to the phosphate deficient environment or microbial environment will have a significant impact on the ecology.For example, the rise of one kind of creature will cause the death of other creatures, and the decrease of the number of one kind of creature will cause the lack of resources such as oxygen (including eutrophication).In the case of pollution, phosphate is the main component of total dissolved solids (a major water quality indicator).[2]
purpose
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Chemical fertilizer industry
Phosphate is generally used in detergents as a water softener, but because the boom and decline cycle of algae will affect the discharge of phosphate at the watershed, phosphate detergents are controlled in some areas.
In agriculture, phosphate is one of the three main nutrients of plants and the main component of fertilizers.Phosphate rock powderIs fromsedimentary rockIn the phosphorus layer.In the past, it can be used without processing after mining, but now the unprocessed phosphate is only used fororganic farming On.It is generally made by chemical processingSuperphosphate lime、Double superphosphateorAmmonium dihydrogen phosphateTheir concentration is higher than that of phosphate, and they are more soluble in water, so plants can absorb them quickly.
The fertilizer grade generally has three numbers: the first refers to the amount of nitrogen, the second refers to the amount of phosphate, and the third refers to alkaline water.So a 10-10-10 fertilizer has 10% of each ingredient, while the others are fillers.
Phosphate in runoff from over fertilized farmland may be the cause of eutrophication, red tide and subsequent hypoxia.Just like phosphate detergent, it can cause anoxia of fish and other aquatic organisms.[3]
Refractory
Phosphates are used as binders in refractories.Phosphate binder is a refractory binder with acid orthophosphate or polycondensation phosphate as the main compound and cementitious property.The binding form of phosphate binder is chemical reaction binding or polymerization binding.Most of the binders made by the reaction of phosphoric acid with alkali metals or alkaline earth metal oxides and their hydroxides are pneumatic binders, which means that condensation and hardening can occur at room temperature without heating.Most of the binders made by the reaction of phosphoric acid with amphoteric oxides, hydroxides or acid oxides are thermosetting binders, that is, they must be heated to a certain temperature to react before condensation and hardening can occur.Phosphate used as the binder of refractories has strong bonding strength in the middle and low temperature range before ceramic bonding, so it is widely used as the binder of unshaped refractories and unfired refractories.[3]
Food industry
Phosphorus is an important mineral element necessary for the human body. The main source of phosphorus ingested by the human body is natural food or food phosphate additives. Phosphate is one of the natural ingredients of almost all foods.Because phosphate can improve or endow food with a series of excellent properties, it was used in food processing as early as more than 100 years ago, and was widely used after the 1970s.Phosphate is one of the most widely used and large amount of food additives. As an important food ingredient and functional additive, phosphate is widely used in the processing of meat products, poultry products, seafood, fruits, vegetables, dairy products, baking products, beverages, potato products, seasonings, convenience foods, etc.Phosphates used in food processing are usually sodium salt, calcium salt, potassium salt, and iron salt and zinc salt as nutrition enhancers. There are more than 30 kinds of commonly used food grade phosphates. Sodium phosphate is the main consumption type of food phosphate in China. With the development of food processing technology, the consumption of potassium phosphate is also increasing year by year.
In order to give full play to various phosphates and the synergistic effect between phosphates and other additives, and meet the development needs of food processing technology, various compound phosphates are often used as food ingredients and functional additives in practical applications. The research and development of compound phosphates has increasingly become the development direction of the development and application of phosphate food additives.[4-5]
food industry
According to the American Food Chemical Pharmacopoeia (FCC), the functions of phosphates in the food industry can be divided into 15 categories:
It can be seen from the above that phosphate has two main functions in food processing: one is quality improver, and the other is nutrition enhancer.[4]
