CAS: 7758-29-4
Food additive: E451(i)
Typical pH (1%): 9.5–10.0
Typical P2O5: 57–59%
Assay (typical): ≥ 94%
Compliance note: Food-grade and industrial-grade STPP follow different impurity controls. Industrial/technical grade STPP must not be used in food applications.
Quick Answers
Definition: STPP is a linear polyphosphate salt (Na5P3O10) typically containing 57–59% P2O5 and assay ≥ 94%.
Core mechanisms: Chelation of Ca2+/Mg2+, particle dispersion, and pH buffering (1% solution: pH 9.5–10.0).
Food use range: 0.2–0.5% (typical finished-product basis); seafood soaking solutions are commonly 0.3–0.5% at 4–8°C for 30–60 minutes (process-dependent).
Industrial use range: Powder detergents commonly include 10–40% STPP (formulation basis); ceramic slurry dosage is often 0.1–0.5% of dry material (process-dependent).
Internal links (recommended):
1) What is STPP? (Chemistry & key properties)
1.1 Definition
Sodium tripolyphosphate (STPP)—also known as pentasodium triphosphate—is a linear condensed phosphate salt with the chemical formula
Na5P3O10 and CAS number 7758-29-4. In food applications, STPP may be labeled as E451(i).
1.2 Technical properties (typical)
| Parameter | Typical value / description |
|---|---|
| Appearance | White powder or granules; hygroscopic (moisture-sensitive) |
| Solubility | Water-soluble; insoluble in ethanol (20°C: approx. 14 g / 100 g water) |
| pH (1% solution) | Typically 9.5–10.0 |
| Core functions | Chelation (sequestration), dispersion support, pH buffering; water-holding support in protein systems |
1.3 Phosphorus ≠ Phosphate ≠ STPP (concept map)
Elemental Phosphorus (P)
Phosphoric Acid (H3PO4)
Polymerization
STPP (Na5P3O10)
Unit reminder: Some reports use “mg P/L” while others use “mg PO4/L”.
Conversion: 1 mg P ≈ 3.07 mg PO4.
2) Operating or Technical Mechanism
2.1 Chelation of divalent ions
STPP forms soluble complexes with Ca2+ and Mg2+ ions, reducing hardness effects in detergents and water systems and decreasing scale formation potential.
2.2 Particle dispersion
STPP can adsorb onto particle surfaces and increase electrostatic repulsion, reducing agglomeration in ceramic slurries and detergent suspensions.
2.3 pH buffering
A 1% aqueous solution of STPP typically has pH 9.5–10.0. Alkalinity can improve surfactant performance and influence protein-water interactions in food systems.
2.4 Protein interaction in food systems
In meat and seafood processing, STPP can increase ionic strength and affect myofibrillar proteins, contributing to water-holding capacity and texture stability (process-dependent).
3) Key Parameters (typical)
- Chemical formula: Na5P3O10
- CAS: 7758-29-4
- Molecular weight: 367.86 g/mol
- Assay: ≥ 94% (common commercial grade)
- P2O5 content: 57–59%
- pH (1% solution): 9.5–10.0
- Solubility (20°C): approx. 14 g / 100 g water
- Bulk density: 0.8–1.0 g/cm³ (process-dependent)
- Food use (typical): 0.2–0.5% (finished product basis)
- Seafood soaking solution: 0.3–0.5% at 4–8°C for 30–60 min (process-dependent)
- Powder detergents: 10–40% (formulation basis)
- Ceramic slurry dosage: 0.1–0.5% (dry material basis)
Values vary by applicable standard, formulation, and process conditions; verify the latest COA/TDS for the supplied grade.
4) Regulatory references (selected)
4.1 Regulatory snapshot
| Region / body | Reference type | Reference |
|---|---|---|
| United States (FDA) | Code of Federal Regulations (GMP reference) | 21 CFR §182.1810 • FDA “Substances Added to Food” |
| WHO / JECFA | Food additives database entry | WHO JECFA entry |
| European Union | Additives database (category conditions) | EC Additives Database |
4.2 Impurity limits (illustrative examples)
Food-grade STPP is typically controlled to impurity limits defined by the applicable standard (e.g., FCC/JECFA). Always verify the latest COA for the supplied batch and target market.
| Impurity | Example limit (may vary by standard) | Reason |
|---|---|---|
| Fluoride (F) | ≤ 50 mg/kg | Purity control |
| Arsenic (As) | ≤ 3 mg/kg | Heavy metal control |
| Lead (Pb) | ≤ 4 mg/kg | Heavy metal control |
Spec reference example:
FAO/JECFA monograph (Pentasodium Triphosphate, PDF)
5) Application Scenarios (Food + Industrial)
5.1 Food applications (Food grade STPP / E451(i))
| Application | What STPP does | Typical process window (examples) |
|---|---|---|
| Meat & poultry (injection / tumbling) | Supports water-holding capacity and protein functionality (process-dependent). | Typical use: 0.2–0.5% (finished product basis) |
| Frozen seafood (shrimp / fish) | Reduces drip loss during thawing and supports texture stability. | Soaking solution: 0.3–0.5%; 4–8°C; 30–60 minutes |
| Dairy (select uses) | Protein interaction and stability support (formulation-dependent). | Usage is category-dependent; verify local limits |
| Processing aids | Chelation support for stability (case-dependent). | Verify category conditions and labeling requirements |
5.2 Industrial applications (Industrial grade STPP)
| Industry | Role | Typical use range (examples) |
|---|---|---|
| Detergents & cleaning | Builder / water softener | Powder detergents: 10–40% (formulation basis) |
| Ceramics | Deflocculant / dispersant aid | 0.1–0.5% (dry material basis) |
| Water treatment | Hardness control / chelation | Dosing is system-dependent; monitor hardness and scaling indices |
| Other processes | Textile, paper, drilling fluids | Case-dependent |
5.3 Quick Comparison: STPP vs SHMP vs TSPP
| Feature | STPP | SHMP | TSPP |
|---|---|---|---|
| Full name | Sodium Tripolyphosphate | Sodium Hexametaphosphate | Tetrasodium Pyrophosphate |
| Structure | Linear polyphosphate | Cyclic polyphosphate | Pyrophosphate |
| pH (1% solution) | 9.5–10.0 | 6.0–7.5 | 10.0–11.0 |
| Primary function | Chelation + dispersion support | Sequestration + dispersion support | Buffering + emulsification support |
| Typical focus | Detergents; food moisture retention (category-dependent) | Water treatment; dispersion systems | Some food systems; industrial processes |
| View product | STPP | SHMP | TSPP |
6) Grade selection (Food grade vs Industrial grade)
| Dimension | Food Grade STPP (E451(i)) | Industrial Grade STPP |
|---|---|---|
| Primary control | Food additive standard + impurity limits | Industrial performance specifications |
| Heavy metals / fluoride | Controlled to food-grade limits | Not controlled to food additive limits |
| Typical uses | Meat/seafood and food processing (category-dependent) | Detergents, ceramics, water treatment |
| Packaging focus | Food-contact packaging practices may apply | Industrial packaging options |
7) Failure Causes or Risk Factors
- Overdosing in food systems: Exceeding category limits or process targets can affect texture and compliance.
- Incorrect grade selection: Using industrial/technical grade in food systems can violate impurity controls.
- Incomplete dissolution: Low temperature or insufficient mixing can reduce effective concentration.
- Moisture exposure: Hygroscopic uptake can accelerate hydrolysis and affect functional performance.
- COA not verified: Assay and P2O5 variations can change dosing and performance expectations.
- Water chemistry not monitored (industrial): Hardness, alkalinity, and scaling tendency affect effective dosing.
FAQ
Is STPP the same as phosphorus?
No. Phosphorus (P) is an element; phosphate (PO43−) is a stable ion; STPP is a polyphosphate salt. Unit conversion: 1 mg P ≈ 3.07 mg PO4.
What is sodium tripolyphosphate mainly used for?
Common uses include detergent building (hardness control), food moisture retention (category-dependent), ceramic slurry dispersion, and hardness-related control in certain water systems.
What is the typical P2O5 content of STPP?
Commercial STPP commonly contains 57–59% P2O5.
What is the difference between food-grade and industrial-grade STPP?
Food-grade STPP follows food additive standards with stricter impurity limits; industrial-grade STPP is specified for industrial performance. Industrial/technical grade must not be used in food.
Why is STPP used in shrimp and fish?
Food-grade STPP is used to improve water retention and reduce drip loss during freezing/thawing. Typical soaking solutions are 0.3–0.5% at 4–8°C for 30–60 minutes (process-dependent).
Is STPP allowed in the EU and the U.S.?
It is permitted under specific conditions. In the U.S., references include 21 CFR §182.1810; in the EU, use conditions are listed in the EU food additives database (category-dependent).
What is the difference between STPP and SHMP?
STPP is typically alkaline (pH 9.5–10.0 at 1%) and used for hardness control and dispersion support; SHMP is nearer neutral (pH 6.0–7.5 at 1%) and often used for sequestration and dispersion (application-dependent).
How should STPP be stored?
Store in a dry, sealed environment protected from moisture. Moisture exposure can promote hydrolysis and caking.
Documents (COA / TDS / SDS)
To support qualification and compliance checks, document requests commonly include COA, TDS, and SDS. Provide application details to match the appropriate grade and typical specification set.
Information commonly requested for document matching:
- Application (shrimp soaking / meat injection / ceramics slurry / detergent)
- Process conditions (time, temperature, water hardness, target yield/texture)
- Destination market (US / EU / SEA)
- Packaging needs (25 kg / 1000 kg; palletized; inner liner)
Downloads / links:
Final usage levels and labeling depend on local regulations and product category. Verify requirements with QA/regulatory review.
Related reading:
Phosphates encyclopedia •
STPP vs SHMP (water treatment) •
STPP & SHMP (seafood)
