Sodium tripolyphosphate (STPP), the sodium salt of the polyphosphate penta-anion, also known as pentasodium tripolyphosphate or sodium triphosphate (different with trisodium phosphate), is a synthetic ingredient mainly used for retaining moisture in fish. The European food additive number for it is E451(i).
A polyphosphate is formed by a number of simple phosphate units linked together, and sodium tripolyphosphate contains three such units.
The brief manufacturing processes are as follows (1) :
- STPP is commercially produced by the neutralization of phosphoric acid with sodium hydroxide to form the mixture of monosodium phosphate and disodium phosphate.
- Then heat the mixture to 500-550 °C. Here is the reaction equation: NaH2PO4 + 2Na2HPO4 → Na5P3O10 + 2H2O
Food grade STPP exists as two forms, and follows the corresponding chemical formula:
- STPP Anhydrous: Na5O10P3
- STPP Hexahydrate: Na5O10P3 · 6H2O
|Appearance||White powder or granular powder|
|Solubility||Soluble in water, insoluble in ethanol|
|PH||9.1 to 10.2 (1 % solution)|
With the capability of maintaining water, the primary uses of food grade sodium tripolyphosphate are to improve the eating quality in food processing, especially in meat and fish products. It is also applied in pet food (e.g. cat and dog food) for the purpose of binding water and keeping the animal feed fresh.
It may also be used as a food starch modifier.
With the functions of chelating metal ions, suspending, dispersing, emulsifying, pH buffering, and etc, technical grade STPP is widely used in the production of laundry detergents & dishwashing detergents, industrial water softener, industrial cleaner, a grease remover, leather pre-tanning agent, dyeing auxiliary agent and so on.
Let’s see its detailed uses in fish and meat.
STPP is a common ingredient added to fish (e.g. salmon) before frozen and its primary purpose is to reduce the amount of thaw water (or maintain water) and make seafood look firmer and smoother. You may also find it in other frozen seafood, such as scallops, shrimp, and lobster.
The taste, odor, texture, and juiciness are important properties of seafood but most seafood is easily damaged caused by ice crystals and the protein denaturation during the freezing storage.
It is the protein in fish meat that determines the water retention performance. Polyphosphate is a widely used water-retaining agent for seafood to prevent protein denaturation during freezing.
In the production of frozen fish fillets, the fish fillets are soaked in a solution of sodium tripolyphosphate with a certain concentration before freezing.
The level of water retention performance is closely related to the quality of fish products such as texture, tenderness, sliceability, elasticity, and taste. If without sodium tripolyphosphate, when thawed, most seafood is prone to lose weight (water) and generate a darker appearance and as well make the body fragile.
Phosphate is widely used in meat processing and its main purposes are as follows:
- Water retention, emulsification stability, juiciness and tenderness
- Delaying the rate of oxidative spoilage
- Improving color and maintaining flavor
Polyphosphates are commonly used additives in meat processing. The addition of STPP to meat improves texture & color, reduces cooking loss, and increases product yield. Such a mechanism is believed through increasing pH, strengthening ionic power, and chelating metal ions.
STPP interacts with amino acids or hydroxyl groups in proteins, thus improving the water retention and gel strength of meat.
Meanwhile, its combination with sodium chloride can reduce the sodium content in meat compared with using sodium chloride only. NaCl contains 39.3% sodium, while in sodium tripolyphosphate (anhydrous) the sodium content is only 31.3%.
Yes, food grade STPP is a multiple purpose ingredient that is generally recognized as safe (GRAS) when used in food in accordance with good manufacturing practice by the U.S. Food and Drug Administration (FDA) (2).
Also, the safety of STPP has been approved by the European Food Safety Authority (EFSA) and it is an authorized food additive in the European Union (EU) and can be used as a carrier in the preparations of the colour anthocyanins, also applied in the salted fish of the Gadidae family (3), as well as by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) as a sequestrant, texturizer, and thickener. (4)
However, some consumers think it is bad for our health as it is a chemical used in detergents that cannot be eaten, and along with other possible side effects, such as allergy reactions.
Now you may have a good knowledge of the food additive – Sodium Tripolyphosphate (E451i, STPP), from production, uses in fish and meat, approved safety, possible side effects and so on.
Have you noticed this ingredient in the fish shops and seafood restaurants, or in the labels of other kinds of food packagings? Let me know in the comments.