metabisulfat

Metabisulfat (metabisulfate) refers to salts containing the metabisulfite anion, S2O5^2−. The most common forms are sodium metabisulfite (Na2S2O5) and potassium metabisulfite (K2S2O5). These are typically white crystalline solids that dissolve readily in water and can release sulfur dioxide under acidic conditions or when heated.

In aqueous solutions metabisulfite species exist in equilibrium with bisulfite (HSO3−) and sulfite (SO3^2−) forms. They act as reducing agents and antioxidants, helping to prevent oxidation in various applications. They are relatively prone to oxidation themselves and can release sulfur dioxide gas when exposed to heat or strong acids.

Applications of metabisulfates include food and beverage preservation, where they serve as antioxidants and color stabilizers. They are used in winemaking to prevent oxidation and microbial spoilage, in dried fruits and some fruit juices to preserve color, and in certain baked products and starches as a bleaching or conditioning agent. Metabisulfites are also employed in photography, textile processing, and as dechlorination agents in water treatment to neutralize residual chlorine.

Handling and safety considerations are important. Metabisulfites can irritate the eyes, skin, and respiratory tract, and some individuals have sulfite sensitivity or asthma that reacts to these compounds. They may release sulfur dioxide when dissolved in acids or heated, so they should be kept away from acids, stored in a cool, dry place, and handled with appropriate protective equipment. Proper labeling and adherence to regulatory limits for food and industrial use are advised.