INS 339 (ii) is disodium hydrogen phosphate, also known as disodium phosphate, numbered E339(ii) in Europe. It is the middle member of the sodium phosphates (INS 339): with two sodium atoms it sits between the acidic monosodium salt (i) and the strongly alkaline trisodium salt (iii). Dissolved in water it is mildly alkaline.
It is produced by neutralising phosphoric acid with sodium carbonate or sodium hydroxide. Codex lists it as an acidity regulator, emulsifier, emulsifying salt, humectant, sequestrant, stabilizer and thickener.
Its best-known job is as an emulsifying salt in processed cheese, where it keeps melted cheese smooth instead of letting it separate into fat and protein. On SeekSnack it turns up in cheese and barbecue flavours from Lay’s, such as Lay’s Play 3D Cheese Pizza, where the label lists it as an acidity regulator in the seasoning.
