E339I - Monosodium phosphate
Synonyms: E339iMonosodium phosphateMonosodium monophosphateAcid monosodium monophosphateMonosodium orthophosphateMonobasic sodium phosphate
Belongs to: E339 - Sodium phosphates
Products: Found in 126 products
Monosodium phosphate (E339i) is a sodium salt of phosphoric acid used to control acidity, stabilize textures, and help ingredients blend smoothly. You’ll most often see it in processed cheese, powdered drinks, dairy products, and baking mixes, where it works as a buffer, emulsifying salt, and moisture holder.
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At a glance
- What it is: The monobasic (acidic) sodium salt of phosphoric acid; also called monobasic sodium phosphate, monosodium orthophosphate, or sodium dihydrogen phosphate.
- What it does: Acts as an acidity regulator and buffer, an emulsifying salt in cheeses, a stabilizer and thickener, a humectant (helps retain moisture), and a sequestrant (binds trace metals to protect color and flavor).
- Where it’s found: Processed and spreadable cheeses, dairy and plant-based drinks, meat and seafood brines, instant beverages, desserts, and some baking powders.
- Label names: “Monosodium phosphate,” “sodium dihydrogen phosphate,” “E339i,” or grouped as “sodium phosphates.”
- Dietary notes: Adds phosphorus and sodium to the diet; some people need to limit one or both.
- Suitability: Mineral-based; typically suitable for vegetarian and vegan diets.
Why is Monosodium phosphate added to food?
Food makers use monosodium phosphate to keep acidity (pH) in a narrow range so flavors stay consistent and proteins don’t curdle. In processed cheese, it works as an “emulsifying salt,” which helps fat and water stay mixed for a smooth, sliceable texture; U.S. standards of identity for pasteurized process cheese list monosodium phosphate among permitted emulsifying salts.1 It can also bind trace metals (as a sequestrant) to reduce discoloration and off-flavors, and it helps powders dissolve cleanly.
What foods contain Monosodium phosphate?
You’ll most often find it in:
- Processed and spreadable cheeses and cheese slices
- Dairy and plant-based beverages, chocolate milk, and creamers
- Meat, poultry, and seafood brines or marinades
- Instant drink mixes and dessert powders
- Ready-to-mix baking products and some baking powders
- Breakfast cereals and cereal bars
- Certain canned or jarred foods where pH control and texture stability are needed
On labels, it may appear on its own or as part of “sodium phosphates,” alongside related salts like disodium phosphate and trisodium phosphate.
What can replace Monosodium phosphate?
Alternatives depend on the job it’s doing:
- For buffering and acidity control: citric acid or sodium citrates
- For emulsifying cheese: sodium citrates or other food-grade phosphates used as emulsifying salts
- To reduce sodium: potassium phosphates can serve similar functions with less sodium
- For leavening or pH in baking: sodium bicarbonate, sodium carbonate, or calcium/phosphate systems such as calcium phosphates
Keep in mind that performance differs; not every substitute will give the same taste, texture, or stability.
How is Monosodium phosphate made?
Food-grade monosodium phosphate is produced by partially neutralizing phosphoric acid with a sodium base—typically sodium hydroxide or sodium carbonate—to reach the monobasic (acidic) form. The European Union’s additive specifications describe this preparation route and set purity criteria for sodium phosphates (E339), including monosodium phosphate.2
Is Monosodium phosphate safe to eat?
In the United States, monosodium phosphate (sodium phosphate, monobasic) is “generally recognized as safe” (GRAS) when used in line with good manufacturing practice.3 In the European Union, phosphates are allowed as food additives with compositional specifications. The European Food Safety Authority (EFSA) set a group acceptable daily intake (ADI) for phosphates of 40 mg phosphorus per kilogram of body weight per day, covering E338–E341, E343, and E450–E452.4 This ADI applies to total phosphate intake from additives (not from natural foods).
Does Monosodium phosphate have any benefits?
Its benefits are technological, not nutritional. It:
- Keeps pH steady so flavors and colors stay consistent
- Helps processed cheese melt and slice evenly
- Improves dissolving of powders and helps retain moisture
- Binds metal ions to protect taste and appearance
These functions can improve quality and shelf stability, but they don’t make the food inherently “healthier.”
Who should avoid Monosodium phosphate?
- People with chronic kidney disease (CKD) are often advised to limit phosphorus, especially from phosphate additives, because impaired kidneys have trouble clearing excess phosphate.5
- Anyone on a low-sodium diet may wish to watch intake, since this additive contributes some sodium.
- EFSA noted that high consumers in certain age groups can exceed the phosphate ADI from additive sources alone, so children and heavy consumers of phosphate-containing processed foods may need extra care.4
If you have CKD or a prescribed diet, follow your clinician’s advice and check ingredient lists.
Myths & facts
- “It’s the same as harsh cleaning phosphates.” Fact: Monosodium phosphate is a specific food-grade salt used in tiny amounts for pH control and emulsifying; safety depends on the compound, its purity, and how it’s used in food.
- “It’s just a preservative.” Fact: It can help preserve quality by managing pH and binding metals, but it’s mainly a buffer and emulsifying salt, not a primary antimicrobial.
- “All phosphates are interchangeable.” Fact: Different phosphate salts (mono-, di-, tri-, and polyphosphates) have different pH effects and functions; formulators choose among monosodium, disodium, trisodium, and polyphosphates for specific results.
Monosodium phosphate in branded foods
You can spot it on ingredient lists as “monosodium phosphate,” “sodium dihydrogen phosphate,” “E339i,” or grouped under “sodium phosphates.” It’s common in big-brand processed cheese slices and spreads, flavored dairy drinks, instant drink and dessert mixes, meat and seafood products that are brined or marinated, and some breakfast cereals. Check the ingredient panel rather than the front of pack—phosphate salts are usually listed near other acidity regulators, stabilizers, or emulsifiers.
References
Footnotes
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21 CFR 133.169 — Pasteurized process cheese. ecfr.gov https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-133/section-133.169 ↩
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Commission Regulation (EU) No 231/2012 — Specifications for food additives (E 339 Sodium phosphates). eur-lex.europa.eu https://eur-lex.europa.eu/eli/reg/2012/231/oj ↩
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21 CFR 182.1778 — Sodium phosphate, monobasic (GRAS). ecfr.gov https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-182/subpart-B/section-182.1778 ↩
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Re-evaluation of phosphoric acid–phosphates–di-, tri- and polyphosphates (E 338–341, E 343, E 450–452). EFSA Journal 2019;17(6):5674. efsa.europa.eu https://www.efsa.europa.eu/en/efsajournal/pub/5674 ↩ ↩2
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Phosphorus in diet — MedlinePlus, National Library of Medicine (NIH). https://medlineplus.gov/ency/article/002424.htm ↩
Popular Questions
Is monosodium phosphate bad for you?
At permitted food levels E339(i) is generally considered safe; EFSA has set a group ADI for phosphates of 40 mg/kg body weight per day (as phosphorus). Very high intakes may be a concern for people with kidney disease or those needing to limit sodium/phosphate.
Explain why an aqueous solution of monosodium phosphate would be ineffective?
As a buffer near neutral pH, a solution of only monosodium phosphate (NaH2PO4) is too acidic and lacks its conjugate base; effective phosphate buffering requires a mixture of mono- and disodium phosphate (H2PO4−/HPO42−) at the target pH.
How does monosodium phosphate make gas?
In leavening systems it acts as an acid that reacts with baking soda (sodium bicarbonate) to release carbon dioxide gas, which aerates doughs and batters; by itself it does not generate gas.
How to change the ph of protein solution without precipitation using monobasic sodium phosphate?
Use a phosphate buffer pair: slowly titrate with small amounts of monobasic (NaH2PO4) and disodium phosphate (Na2HPO4) to reach the target pH, staying away from the protein’s isoelectric point and keeping the buffer modest (e.g., ~10–50 mM). Make adjustments gradually with constant stirring and temperature, maintaining ionic strength (a little NaCl can help) to minimize precipitation.
How to clean up monosodium phosphate?
For small spills, avoid dust, sweep or scoop up the solid and rinse the area with water; for solutions, absorb with inert material and dispose according to local regulations. Because it’s highly water‑soluble and nutrient-rich, avoid flushing large amounts to drains or waterways.
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