Disodium pyrophosphate or sodium acid pyrophosphate (SAPP)
is an
inorganic compound
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...
consisting of sodium cations and
pyrophosphate
In chemistry, pyrophosphates are phosphorus oxyanions that contain two phosphorus atoms in a P–O–P linkage. A number of pyrophosphate salts exist, such as disodium pyrophosphate (Na2H2P2O7) and tetrasodium pyrophosphate (Na4P2O7), among other ...
anion. It is a white, water-soluble solid that serves as a
buffering and
chelating agent
Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These ligands are ...
, with many applications in the food industry. When crystallized from water, it forms a hexahydrate, but it dehydrates above room temperature. Pyrophosphate is a
polyvalent anion with a high affinity for polyvalent cations, e.g. Ca
2+.
Disodium pyrophosphate is produced by heating
sodium dihydrogen phosphate
Monosodium phosphate (MSP), also known as monobasic sodium phosphate and sodium dihydrogen phosphate, is an inorganic compound of sodium with a dihydrogen phosphate (H2PO4−) anion. One of many sodium phosphates, it is a common industrial chemical ...
:
:2 NaH
2PO
4 → Na
2H
2P
2O
7 + H
2O
Food uses
Disodium pyrophosphate is a popular
leavening agent
In cooking, a leavening agent () or raising agent, also called a leaven () or leavener, is any one of a number of substances used in doughs and batters that cause a foaming action (gas bubbles) that lightens and softens the mixture. An alterna ...
found in
baking powder
Baking powder is a dry chemical leavening agent, a mixture of a carbonate or bicarbonate and a weak acid. The base and acid are prevented from reacting prematurely by the inclusion of a buffer such as cornstarch. Baking powder is used to increas ...
s. It combines with sodium bicarbonate to release carbon dioxide:
: Na
2H
2P
2O
7 + NaHCO
3 → Na
3HP
2O
7 + CO
2 + H
2O
It is available in a variety of grades that affect the speed of its action. Because the resulting phosphate residue has an off-taste, SAPP is usually used in very sweet cakes which mask the off-taste.
![Tin, food product (AM 2015](https://upload.wikimedia.org/wikipedia/commons/1/10/Tin%2C_food_product_%28AM_2015.4.24-2%29.jpg)
Disodium pyrophosphate and other
sodium and potassium polyphosphates are widely used in food processing; in the
E number
E numbers ("E" stands for "Europe") are codes for substances used as food additives, including those found naturally in many foods such as vitamin C, for use within the European Union (EU) and European Free Trade Association (EFTA). Commonly ...
scheme, they are collectively designated as
E450, with the disodium form designated as E450(a). In the United States, it is classified as
generally recognized as safe (GRAS) for food use. In canned seafood, it is used to maintain color and reduce purge during
retorting
In a chemistry laboratory, a retort is a device used for distillation or dry distillation of substances. It consists of a sphere, spherical vessel with a long downward-pointing neck. The liquid to be distilled is placed in the vessel and heate ...
. Retorting achieves microbial stability with heat. It is an acid source for reaction with baking soda to leaven baked goods.
In baking powder, it is often labeled as food additive E450. In
cured meat
Curing is any of various food preservation and flavoring processes of foods such as meat, fish and vegetables, by the addition of salt, with the aim of drawing moisture out of the food by the process of osmosis. Because curing increases the solu ...
s, it speeds the conversion of
sodium nitrite
Sodium nitrite is an inorganic compound with the chemical formula NaNO2. It is a white to slightly yellowish crystalline powder that is very soluble in water and is hygroscopic. From an industrial perspective, it is the most important nitrite ...
to
nitrite
The nitrite polyatomic ion, ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name ...
(NO
2−) by forming the
nitrous acid
Nitrous acid (molecular formula ) is a weak and monoprotic acid known only in Solution (chemistry), solution, in the gas phase and in the form of nitrite () salts. Nitrous acid is used to make diazonium salts from amines. The resulting diazoni ...
(HONO) intermediate, and can improve water-holding capacity. Disodium pyrophosphate is also found in frozen
hash brown
Hash browns, also spelled hashed browns, are a popular American and British breakfast food, consisting of finely chopped potatoes that have been fried until browned. Hash browns first started appearing on breakfast menus in New York City in th ...
s and other
potato
The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae.
Wild potato species can be found from the southern Unit ...
products, where it is used to keep the color of the potatoes from
darkening.
[
Disodium pyrophosphate can leave a slightly bitter aftertaste in some products, but "the
SAPP taste can be masked by using sufficient baking soda and by adding a source of calcium ions, sugar, or flavorings."][
]
Other uses
In leather
Leather is a strong, flexible and durable material obtained from the tanning, or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from cattle, sheep, goats, equine animals, buffalo, pigs and hogs, ...
treatment, it can be used to remove iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
stains on hides during processing. It can stabilize hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%†...
solutions against reduction. It can be used with sulfamic acid
Sulfamic acid, also known as amidosulfonic acid, amidosulfuric acid, aminosulfonic acid, sulphamic acid and sulfamidic acid, is a molecular compound with the formula H3NSO3. This colourless, water-soluble compound finds many applications. Sulfami ...
in some dairy applications for cleaning, especially to remove soapstone. When added to scalding water, it facilitates removal of hair and scurf in hog slaughter and feathers and scurf in poultry slaughter. In petroleum production, it can be used as a dispersant
A dispersant or a dispersing agent is a substance, typically a surfactant, that is added to a suspension of solid or liquid particles in a liquid (such as a colloid or emulsion) to improve the separation of the particles and to prevent their se ...
in oil well drilling muds. It is used in cat foods as a palatability additive.
Disodium pyrophosphate is used as a tartar control agent in toothpastes.
References
External links
*{{Commons category-inline
Pyrophosphates
Sodium compounds
Edible thickening agents