- Trisodium citrate (E331, sodium citrate) is the sodium salt of citric acid – an acidity regulator, buffer, sequestrant and emulsifying salt.
- Unlike citric acid, it does not acidify: it is slightly alkaline (pH 7.5–9) and has a salty taste.
- In medicine it prevents blood from clotting in test tubes and transfusion bags and alkalises urine.
- EFSA confirmed its safety in 2020; mainly people on a low-sodium diet should be careful – 1 g of the dihydrate provides about 235 mg of sodium.
In short: trisodium citrate (sodium citrate, E331) is the sodium salt of citric acid, usually sold as the dihydrate. In food it acts as an acidity regulator, buffer, sequestrant and emulsifying salt, e.g. in beverages, processed cheese and jams. In medicine it is used as an anticoagulant in coagulation test tubes and blood bags. It is safe, but – like any sodium salt – it adds sodium to the diet.
Other names include sodium citrate, trisodium citrate, the trisodium salt of citric acid and E331(iii). It is made by neutralising citric acid with sodium hydroxide, carbonate or bicarbonate, followed by crystallisation. The name “sodium citrate” can be ambiguous, because E331 covers three salts: mono-, di- and trisodium citrate.
| Parameter | Trisodium citrate, anhydrous | Trisodium citrate dihydrate |
|---|---|---|
| Formula | C6H5Na3O7 | C6H5Na3O7·2H2O |
| Molar mass | 258.07 g/mol | 294.10 g/mol |
| CAS number | 68-04-2 | 6132-04-3 |
| Sodium content | approx. 26.7% | approx. 23.5% |
| pH of a 5% solution | 7.5–9.0 (slightly alkaline) | |
| Solubility | very soluble in water, practically insoluble in ethanol | |
Properties of trisodium citrate
Trisodium citrate comes as white, odourless crystals, granules or powder with a salty, slightly tart taste. It is hygroscopic, so it should be stored in tightly closed packaging in a dry place. Although it is a salt of citric acid, its solution is slightly alkaline (pH 7.5–9).
Its key technological properties are:
- buffering – together with citric acid it keeps the pH of a product stable,
- binding metal ions (calcium, magnesium, iron, copper) – it stabilises colour, limits fat oxidation and softens water,
- emulsifying action in cheese – as an emulsifying salt it breaks down calcium-bound casein, so processed cheese is smooth and does not separate.
Uses for trisodium citrate
Trisodium citrate is used mainly in the food industry, but also in medicine, pharmaceuticals, cosmetics and household chemicals. In food it is not used to acidify – that is the role of citric acid – but to regulate and stabilise acidity and soften an overly sharp, sour taste.
In cosmetics (shampoos, shower gels, creams) it regulates pH and binds metal ions, improving product stability. In cleaning products and descalers it softens water, so detergents work more effectively. In laboratories it is a component of citrate buffers and of Benedict’s reagent for detecting reducing sugars.
Trisodium citrate in the food industry
Trisodium citrate (E331) is authorised in the EU in most food categories at quantum satis, i.e. in the amount needed to achieve the technological effect. It is most often found in:
- beverages – carbonated, energy and isotonic drinks, where it softens acidity and stabilises the taste,
- processed cheese and cheese slices – as an emulsifying salt,
- dairy products – e.g. UHT milk, coffee creamers and milk drinks, where it prevents protein precipitation,
- jams, jellies and gummies – it regulates the pH on which pectin gelling depends,
- meat products, sauces, mayonnaise and seasonings – it stabilises colour and supports antioxidants.
Citrate is not a preservative in the legal sense, but by binding metal ions it slows fat oxidation and colour changes, which indirectly extends shelf life.
Trisodium citrate in medicine
The best-known medical use of sodium citrate is as an anticoagulant. Citrate binds calcium ions, which are essential for blood clotting, which is why it:
- fills light-blue-top tubes for coagulation tests (e.g. INR, APTT) – a 3.2% solution is used in a ratio of 1 part citrate to 9 parts blood,
- is a component of the preservative solutions in blood collection and storage bags and in apheresis,
- is sometimes used to fill haemodialysis catheters as an alternative to heparin, especially in patients at risk of bleeding.
Sodium citrate also alkalises urine, which is why it is used in products that relieve cystitis symptoms and support the treatment of some types of kidney stones. It is an ingredient of the oral rehydration solution recommended by the WHO and of laxative micro-enemas. Medicinal doses should always be discussed with a doctor.
Benefits for athletes
Sodium citrate, like sodium bicarbonate, is an extracellular buffer. In studies it was usually given at about 0.3–0.5 g per kilogram of body weight 1–3 hours before exercise to see whether it delays fatigue during intense efforts lasting a few minutes, e.g. middle-distance running, rowing or cycling.
The results are mixed: some studies showed a small improvement in performance, others no effect. Large doses often cause gastrointestinal discomfort, and because of the sodium they also promote water retention. Sodium citrate is not a prohibited substance in sport, but supplementation is best planned with a sports dietitian and tested in training rather than before a competition.
Mono-, di- and trisodium citrate – what is the difference?
E331 covers three salts of citric acid that differ in the number of sodium atoms and therefore in pH and use:
| Compound | Number | Formula | pH of solution | Typical use |
|---|---|---|---|---|
| monosodium citrate | E331(i) | C6H7NaO7 | approx. 3.5–3.8 (1%) | mild acidification, effervescent powders, beverages |
| disodium citrate | E331(ii) | C6H6Na2O7 | approx. 4.9–5.2 (1%) | buffer, stabiliser |
| trisodium citrate | E331(iii) | C6H5Na3O7 | 7.5–9.0 (5%) | acidity regulator, emulsifying salt, anticoagulant |
Trisodium citrate is the most widely used, which is why it is usually what “sodium citrate” refers to.
Sodium citrate vs citric acid – what is the difference?
Sodium citrate is not the same as citric acid. Citric acid (E330) is an acid, while sodium citrate (E331) is its salt, formed when the acid is neutralised with sodium:
| Property | Citric acid (E330) | Trisodium citrate (E331) |
|---|---|---|
| Formula | C6H8O7 | C6H5Na3O7 |
| Taste | clearly sour | salty, slightly tart |
| pH of a 1% solution | approx. 2.2 (acidic) | approx. 8 (slightly alkaline) |
| Main function | acidification, antioxidant, descaling | pH regulation and stabilisation, emulsifying salt, anticoagulant |
In practice the two are often used together: a mixture of citric acid and sodium citrate forms a buffer that keeps the pH of beverages, jellies or sauces stable. Read more about the acid in the article Citric acid – properties and uses, and about similar additives in 5 acidity regulators used in the food and beverage industry.
Is trisodium citrate harmful?
No. Trisodium citrate is considered safe. In 2020 the European Food Safety Authority (EFSA) re-evaluated citric acid and citrates (E330–E333) and concluded that there is no need to set an acceptable daily intake (ADI) and that their use as additives raises no concern. Citrate is a natural metabolite – the body breaks it down in the Krebs cycle.
Points to watch:
- sodium – 1 g of trisodium citrate (dihydrate) provides about 235 mg of sodium; people with high blood pressure, heart failure or on a low-sodium diet should take this into account (the WHO recommends less than 2 g of sodium a day),
- kidney disease – citrates increase aluminium absorption, so patients with kidney failure should not combine them with aluminium-containing medicines,
- large doses – e.g. in sports supplementation they can cause diarrhoea, nausea and abdominal pain.
In the amounts used in food, sodium citrate poses no risk to healthy people. Foodcom supplies food-grade trisodium citrate and monosodium citrate – for specifications and availability, contact our sales team.
