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Introduction
Magnesium oxide (MgO), also known as magnesia, is a white, basic solid produced by calcining magnesium carbonate or magnesium hydroxide. It has low solubility in water but reacts with acids to form soluble magnesium salts. In food processing, magnesium oxide is used as a pH regulator, as an anticaking agent, as a dietary magnesium source, and as a processing aid in sugar refining.
Unlike calcium oxide, magnesium oxide does not react violently with water; it slowly hydrates to magnesium hydroxide. It is considered a gentle alkali. It is approved as a food additive (E530) in the EU.
CAS Number
1309-48-4
Synonyms
Magnesia, Periclase (mineral), Calcined magnesia, E530.
Topic Headings
1. Use as an anticaking agent and magnesium fortifier (paragraph form)
Magnesium oxide is often added to powdered foods (e.g., salt, sugar, powdered milk, spice blends) to prevent caking. Its fine particles absorb moisture and coat the surfaces of other particles, keeping them free-flowing. It is particularly effective in high-humidity environments. In table salt, magnesium oxide is sometimes added as an anticaking agent (though sodium aluminosilicate or calcium silicate are more common). Additionally, magnesium oxide is used as a magnesium fortificant in foods such as breakfast cereals, infant formulas, and dietary supplements. The oxide is converted to magnesium chloride or magnesium lactate in the stomach (by hydrochloric acid), providing bioavailable magnesium. Typical fortification levels are 50-200 mg of magnesium per serving. Magnesium oxide has the highest magnesium content by weight (60% Mg) of any common magnesium compound, so it is cost-effective for fortification.
2. Physical and chemical properties (list form)
• Appearance — White to off-white fine powder.
• Odor — Odorless.
• Molecular weight — 40.30 g/mol.
• Melting point — 2852°C.
• Solubility in water — 0.0086 g/100 mL at 30°C (very low; forms Mg(OH)₂ on surface, which further limits dissolution).
• Solubility in other solvents — Soluble in dilute acids (forms Mg²⁺ salts); insoluble in ethanol.
• pH (1% suspension) — Approximately 10.5 (basic).
• Density — 3.58 g/cm³.
• Hygroscopicity — Slowly absorbs moisture and CO₂ from air to form magnesium hydroxide and magnesium carbonate.
• Specific surface area — High for "light" grades; low for "heavy" grades.
3. Food applications and typical usage levels (list form)
• Anticaking agent in powdered foods (salt, sugar, spices, milk powder) — 0.1-0.5% by weight.
• Magnesium fortification (breakfast cereals, infant formula, nutritional bars) — Provides 50-200 mg Mg per serving.
• pH regulator in food processing — Small amounts (0.01-0.1%) to raise pH without adding sodium or calcium.
• Sugar refining — Used as a clarification aid (less common than calcium oxide).
• Mineral water carbonation — As a source of magnesium; reacts with carbonic acid to form soluble magnesium bicarbonate.
• Dietary supplements (tablets, capsules) — As a source of elemental magnesium.
• Food packaging (moisture absorbers) — As a desiccant in some food-grade silica gel alternatives.
4. Regulatory status and safety (paragraph form)
Magnesium oxide is approved as a food additive (E530) in the EU for use as an anticaking agent, pH regulator, and magnesium source. In the USA, it is GRAS under 21 CFR 184.1431. JECFA has not set an ADI due to low toxicity; magnesium is an essential nutrient. The UL for supplemental magnesium is 350 mg/day for adults, but magnesium from food sources (including fortified foods) is not limited because absorption is regulated. When ingested, magnesium oxide reacts with stomach acid to form magnesium chloride, which is partially absorbed. At high doses (above 1-2 g of MgO), it has a laxative effect similar to magnesium hydroxide. However, anticaking uses involve very small amounts (milligrams per serving), well below laxative threshold. In fortified foods, typical added magnesium is 50-200 mg per serving, which is safe for most individuals. People with kidney disease may accumulate magnesium and should consult a physician. Unlike calcium oxide, magnesium oxide is not caustic; it is safe to handle with standard dust precautions.
