Disodium pyrophosphate or sodium acid pyrophosphate is an inorganic compound composed of sodium cation and pyrophosphate anion. It is a white, water-soluble solid that can be used as a buffer and chelating agent and has many applications in the food industry. When crystallized from water, it forms hexahydrate but dehydrates above room temperature. Pyrophosphate is a polyvalent anion with a high affinity for polyvalent cations, for example, calcium ions. Disodium pyrophosphate is produced by heating sodium dihydrogen phosphate:
2NaH2PO4 → Na2H2P2O7 + H2O.
The method of preparing sodium acid pyrophosphate having substantially improved doughnut baking properties which comprises thermally evaporating a monosodium orthophosphate solution containing from 0.50% to 0.65% by weight of phosphoric acid together with about 0.10% to about 0.20% K2O and about 0.025% to about 0.075% Al2O3, basis NaH2PO4, to produce substantially dry monosodium orthophosphate, calcining the said monosodium orthophosphate at a temperature of about 225℃. to about 235℃. Until sodium acid pyrophosphate has been formed, and thereafter tempering the said pyrophosphate by maintaining it at atmospheric pressure and at a temperature of about 215℃ to about 245℃. An atmosphere containing 230 mm. to 760 mm. hg of steam, said tempering being carried out for one hour to four hours, and thereafter adding to the said pyrophosphate a basic sodium phosphate to obtain a product having a pH value of from 4.0 to 4.6.
Sodium Acid Pyrophosphate is a popular leavening agent found in baking powders, which used as a constituent of blanching solutions for preventing after-cooking darkening of potatoes. Disodium pyrophosphate is used as a constituent of phosphate mixes in meat processing, and cheese emulsifying salts. In addition, it is used as a general buffer and acidifying agent in foodstuffs. In seafood products, disodium pyrophosphate is used as preservative.
Sodium Acid Pyrophosphate is used as a dispersant in oil well drilling muds in petroleum production. It is also used in leather treatment to remove iron stains. Moreover, Disodium pyrophosphate is also used in the stabilization of hydrogen peroxide solutions. It is used in treatment of kidney stones and skin. It is used in diary cleaning, electroplating and metal surface cleaning.