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E452 Polyphosphates is a group of synthetic food additives (E-numbers) used as emulsifiers, stabilizers, and moisture-retaining agents.
They are commonly added to processed meats, seafood, and dairy products to improve texture, increase juiciness, and extend shelf life.
E452 Polyphosphates are salt or ester of polymeric oxyanions formed from tetrahedral PO4 (phosphate) structural units linked together by sharing oxygen atoms.
Food additive E452 (Polyphosphates) consists of several sodium, potassium, calcium, and ammonium salts of polymeric phosphoric acid. Because it is a diverse chemical group, different variants have their own specific CAS numbers.
Sodium polyphosphate (E452(i)): CAS No. 68915-31-1 (often used as Sodium hexametaphosphate)
Potassium polyphosphate (E452(ii)): CAS No. 7782-95-8
Sodium calcium polyphosphate (E452(iii)): CAS No. 65996-98-7
Calcium polyphosphate (E452(iv)): CAS No. 10101-08-9
Sodium tripolyphosphate (E452(vi)): CAS No. 7758-29-4
E452 Polyphosphates can adopt linear or a cyclic (also called, ring) structures.
In biology, the E452 Polyphosphates esters ADP and ATP are involved in energy storage.
A variety of polyphosphates find application in mineral sequestration in municipal waters, generally being present at 1 to 5 ppm.
GTP, CTP, and UTP are also nucleotides important in the protein synthesis, lipid synthesis, and carbohydrate metabolism, respectively.
E452 Polyphosphates are also used as food additives, marked E452.
The structure of tripolyphosphoric acid illustrates the principles which define the structures of polyphosphates.
E452 Polyphosphates consists of three tetrahedral PO4 units linked together by sharing oxygen centres.
For the linear chains, the end phosphorus groups share one oxide and the others phosphorus centres share two oxide centres.
The corresponding phosphates are related to the acids by loss of the acidic protons.
In the case of the cyclic trimer each tetrahedron shares two vertices with adjacent tetrahedra.
Sharing of three corners is possible.
This motif represents crosslinking of the linear polymer.
Crosslinked E452 Polyphosphates adopt the sheet-structure Phyllosilicates, but such structures occur only under extreme conditions.
Formation and synthesis
E452 Polyphosphates arise by polymerization of phosphoric acid derivatives.
The process begins with two phosphate units coming together in a condensation reaction.
2 H(PO4)2− ⇌ (P2O7)4− + H2O
The condensation is shown as an equilibrium because the reverse reaction, hydrolysis, is also possible.
The process may continue in steps; at each step another (PO3)− unit is added to the chain, as indicated by the part in brackets in the illustration of polyphosphoric acid.
E452 Polyphosphates can be seen as the end product of condensation reactions, where each tetrahedron shares three corners with the others.
Conversely, a complex mix of polymers is produced when a small amount of water is added to phosphorus pentoxide.
Use as food additives
Sodium polyphosphate (E452(i)), potassium polyphosphate (E452(ii)), sodium calcium polyphosphate (E452(iii)) and calcium polyphosphate (E452(iv)) are used as food additives (emulsifiers, humectants, sequestrants, stabilisers, and thickeners).
They are not known to pose any potential health risk other than those generally attributed to other phosphate sources (including those naturally occurring in food).
While concerns have been raised regarding detrimental effects on the bones and cardiovascular diseases, as well as hyperphosphatemia, these seem to be relevant only for exaggerated consumption of phosphate sources.
In all, reasonable consumption (up to 40 mg phosphate per kg of body weight per day) seems to pose no health risk.
