Sodium Hexametaphosphate (SHMP)

About This Product

Sodium hexametaphosphate, usually shortened to SHMP, is a food-grade sodium polyphosphate authorised as E452(i) in the EU and UK. It is identified by CAS number 10124-56-8 (68915-31-1 is also used). Despite the name it is not a single six-unit molecule but a glassy mixture of long-chain sodium polyphosphates, (NaPO3)n, made by melting and rapidly cooling sodium phosphate. It is supplied as clear to white glassy flakes, granules or powder, dissolves readily in water and gives a near-neutral solution.

SHMP is valued above all as a sequestrant. It binds calcium, magnesium and iron ions strongly, disperses proteins and particles, and in blends improves water retention. In fish and shellfish processing it is part of the phosphate systems that limit drip loss and protect texture in frozen fillets, prawns and surimi. In meat products it is usually blended with sodium tripolyphosphate and tetrasodium pyrophosphate. Other uses include processed cheese and dairy products, where it acts as an emulsifying salt and stabiliser, soft drinks where permitted, where it binds water hardness and so improves the efficiency of sorbate preservation, canned seafood, where it helps prevent struvite crystals, and peeled or processed vegetables. Total added phosphate in meat and seafood is typically in the order of 0.3 % to 0.5 % of product weight, within the legal limit.

Because it is a mixture, SHMP is specified by its total P2O5 content, commonly 68 % or more for food grades, with the proportion of inactive or short-chain phosphate controlled. The average chain length affects sequestering power and solubility, so a change of grade can change performance even at the same P2O5 figure. In solution, polyphosphates slowly hydrolyse to pyrophosphate and orthophosphate, faster when hot or acidic, so brines and stock solutions are best made up fresh.

Buyers typically agree the total P2O5 on the ignited basis, inactive P2O5, the pH of a 1 % solution, water-insoluble matter, fluoride and heavy metals including arsenic, cadmium, lead and mercury. The grade should meet the E452(i) purity criteria in Regulation (EU) No 231/2012 and its GB equivalent, or the FCC or JECFA monograph for other markets.

Phosphates E338 to E452 are authorised in specific food categories under Annex II of Regulation (EC) No 1333/2008 and the UK retained equivalent, mostly with a group maximum expressed as P2O5 that covers all added phosphates together. Meat preparations are treated more restrictively than meat products, and fish and crustacean categories carry their own conditions, so check the current annex for the exact product. Declare SHMP by function, for example stabiliser: E452 or stabiliser: sodium polyphosphate.

SHMP is hygroscopic in powder form and should be stored sealed, dry and off the floor; glassy flakes resist caking better. It is not classified as highly hazardous, but dust irritates eyes and airways, so follow the safety data sheet. When you enquire, give the application, the form (flake, granule or powder), minimum P2O5, the purity standard, pack size, annual volume and destination, and the documents you need.