Polarised light micrograph of crystals of sodium citrate. Sodium citrate is the trisodium salt of citric (tricarboxylic) acid. It is used extensively as a food additive, known as E331. It has anti-oxidant and preservative properties and is an acidity regulator. Its main uses are in bottled sauces, pickles, dairy products and bakery. Sodium citrate also has some use as a blood anti-coagulant and blood acidity regulator. Magnification x10 at 35mm size.