Magnesium stearate

About Magnesium stearate

Magnesium stearate is the magnesium salt of the fatty acid, stearic acid. It has been widely used for many decades in the food industry as an emulsifier, binder and thickener, as well as an anticaking, lubricant, release, and antifoaming agent. It is present in many food supplements, confectionery, chewing gum, herbs and spices, and baking ingredients. Magnesium stearate is also commonly used as an inactive ingredient in the production of pharmaceutical tablets, capsules and powders.

For food applications, magnesium stearate is typically manufactured by one of two processes. The direct or fusion process involves direct reaction of fatty acids with a source of magnesium, such as magnesium oxide, to form magnesium salts of the fatty acids. In the indirect or precipitation process, a sodium soap is produced by reacting fatty acids with sodium hydroxide in water and precipitating the product through addition of magnesium salts to the soap. The fatty acids used as raw material are derived from edible fats and oils and consist mainly of stearic and palmitic acid. The final product contains 4.0-5.0% magnesium, on a dried basis, and the fatty acid fraction is composed of ≥90% stearic and palmitic acids, at least 40% of which are stearic acid. It is a very fine powder that is greasy to the touch and practically insoluble in water.

Upon ingestion, magnesium stearate is dissolved into magnesium ion and stearic and palmitic acids. Magnesium is absorbed primarily in the small intestine, and to a lesser extent, in the colon. Magnesium is an essential mineral, serving as a cofactor for hundreds of enzymatic reactions and is essential for the synthesis of carbohydrates, lipids, nucleic acids and proteins, as well as neuromuscular and cardiovascular function. The majority of magnesium content in the body is stored in bone and muscle. A small amount (∼1%) is present in serum and interstitial body fluid, mostly existing as a free cation while the remainder is bound to protein or exists as anion complexes. The kidney is largely responsible for magnesium homeostasis and maintenance of serum concentration.

Magnesium stearate is permitted for use in the European Union and other countries including China, Japan, Australia and New Zealand, and was granted generally recognized as safe (GRAS) status in the United States.

Magnesium stearate is often used as an anti-adherent in the manufacture of medical tablets, capsules and powders. In this regard, the substance is also useful because it has lubricating properties, preventing ingredients from sticking to manufacturing equipment during the compression of chemical powders into solid tablets; magnesium stearate is the most commonly used lubricant for tablets. Magnesium stearate can also be used efficiently in dry coating processes.

In the production of pressed candies, magnesium stearate serves as a release agent. It is also used to bind sugar in hard candies such as mints. Magnesium stearate is a common ingredient in baby formulas. In the EU and EFTA it is listed as food additive E470b.

Magnesium stearate is a major component of bathtub rings. When produced by soap and hard water, magnesium stearate and calcium stearate both form a white solid insoluble in water, and are collectively known as soap scum.