Sodium Acid Pyrophosphate: A Versatile Food Additive and Industrial Agent

CAS Registry Number: 7758-16-9

Overview

Sodium acid pyrophosphate (SAPP), also known as disodium dihydrogen pyrophosphate, is an inorganic compound with the chemical formula Na₂H₂P₂O₇ and a molecular weight of 221.94 g/mol . It is a white, odorless crystalline powder or granules that is soluble in water, producing an acidic solution with a pH of approximately 4.0 (for a 1% solution) . SAPP decomposes when heated above 220°C, forming sodium metaphosphate .

Major Applications

Food Industry

SAPP is a multifunctional food additive widely used across various food categories:

• Leavening Agent: As an acid component in baking powders, SAPP reacts with sodium bicarbonate to release carbon dioxide, providing controlled leavening for baked goods. Different grades of SAPP offer varying reaction rates to suit specific baking applications .

• Sequestrant and Chelating Agent: It binds metal ions such as Ca²⁺, Fe²⁺, and Cu²⁺, helping to prevent discoloration, off-flavors, and nutrient degradation in processed foods .

• Meat and Poultry Processing: SAPP functions as a moisture retention agent and curing accelerator, enhancing juiciness and yield. Maximum usage levels in meat products are limited to 0.5% in the finished product .

• Potato Products: It acts as a color stabilizer, preventing enzymatic browning and discoloration in processed potato products .

• Canned Seafood: SAPP prevents the formation of struvite crystals (magnesium ammonium phosphate) in canned tuna and other seafood products, at levels not exceeding 0.5% by weight .

• Cheese Production: Used as an emulsifying agent in standardized cheese products, with a maximum usage limit of 3% of the finished food weight .

Other Industrial Applications

Beyond food processing, SAPP is used in water treatment (as a surfactant and dispersing agent), as a dispersant in oil well drilling mud, in electroplating and metal cleaning processes, and as an agent in hog and poultry carcass scalding operations .

Regulatory Status

SAPP is generally recognized as safe (GRAS) by the FDA for use in food products under good manufacturing practices . It is listed under FDA regulations for various standardized foods and has an acceptable daily intake (ADI) of 0–70 mg/kg for total phosphates (expressed as phosphorus) . The USDA also permits its use as a leavening agent in organic products under the National Organic Program .

Safety and Handling

Health Considerations

SAPP is generally considered safe at normal usage levels. However, some safety considerations should be noted:

• Irritation: The compound is classified as an irritant, causing irritation to the eyes, skin, and respiratory tract upon direct contact . It is classified with H319 (causes serious eye irritation) under GHS .

• Ingestion Effects: Consumption of high doses may cause gastrointestinal irritation. Absorption of sufficient phosphate can potentially lead to hyperphosphatemia, hypocalcemia, and/or hypomagnesemia .

• Toxicity Data: Oral LD₅₀ in mice is reported at 2650 mg/kg . High usage levels have been associated with kidney stone formation in some reports .

Storage and Handling

• Store in sealed, airtight containers in a dry, cool location .

• Protect from moisture and strong oxidizing agents.

• When preparing aqueous solutions for use, keep temperature below 40°C to minimize hydrolysis