What is Monosodium Phosphate (E339i) in food and its uses?

Production | Property | Uses

Monosodium phosphate (MSP), also called sodium dihydrogen phosphate or sodium phosphate monobasic, is a multifunctional ingredient that can be used as an acid regulator, sequestrant and nutrient supplement in food with the European food additive number E339(i). It is more acidic than disodium phosphate, which is alkaline.

How is it made? 

It can be produced in two ways: partial neutralizing phosphoric acid with sodium carbonate/sodium hydroxide OR the reverse order.

MSP is an inorganic compound made from naturally occurring minerals and existing in three forms, and follows the corresponding chemical formula: 

  1. MSP Anhydrous:  NaH2PO4
  2. MSP Monohydrate: NaH2PO4 · H2O
  3. MSP Dihydrate: NaH2PO4 ·2 H2O


Other names
  • Monosodium orthophosphate
  • Sodium biphosphate
  • Sodium acid phosphate
CAS number 7558-80-7
Appearance A white powder or granular
Solubility Freely soluble in water, insoluble in ethanol
PH An acid with the PH value between 4.1 and 5.0 (1% solution)

What are the uses?

Monosodium phosphate can be used in food, chemical industry, printing and dyeing, metal clean, water treatment (corrosion control), aquaculture, and etc. 

It is generally recognized as safe (GRAS) when used as a nutrient and a sequestrant in food in accordance with good manufacturing practice (1) (2). And its safety has been re-evaluated by EFSA in 2019 and established an ADI expressed as phosphorus of 40 mg/kg body weight (bw) per day. (3)


Food grade monosodium phosphate is generally used in following food lists:

  • A buffer and acidity regulator in food
  • A Leavening acid in baking powder
  • A binder and curing agent for bread and sauce
  • Water retention agent
  • Quality improver for evaporated milk
  • A stabilizer for dairy products, meat, and fish products
  • Cheeses, sweet jellies, jams & preserves, frozen eggs, chocolate products (4)

Animal feed

As a feed additive, sodium dihydrogen phosphate is a good source of phosphorus and sodium for feed (horse) and pet food (e.g. dog, cat).


When used as an ingredient in toothpaste, MSP functions as a PH control and prevents teeth cavities.

Other sodium phosphates

Sodium dihydrogen phosphate can be used to produce various sodium phosphate salts, such as sodium trimetaphosphate, sodium hexametaphosphate, sodium acid pyrophosphate and sodium polyphosphate.


Now you may have a good knowledge of the food additive – monosodium phosphate E339(i), from its production, uses, approved safety and so on.

What kinds of food packaging have you found this ingredient in? Let me know in the comments.


  1. harun
  2. Sarah
  3. Christy Stricker