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Malic acid is a dicarboxylic acid found in many sour or tart-tasting foods. When eaten, it produces a mellow and persistent sour taste. The most common source of this compound is unripe fruit. This acid is also produced within the human body as a part of the citric acid cycle. The salts of malic acid, known as maltates, are an important intermediary step in the cycle.
This acid was originally isolated in an apple by the Swedish chemist Carl Wilhelm Scheele in 1785. In 1787, Antoine-Laurent de Lavoisier, a French chemist, suggested that the newly-discovered acid be named acide malique after the Latin word malum, for apple. Malic acid is crystalline in structure, colorless, and soluble in water.
The most common use of the acid is in food products, notably in candy and potato chips. Sour candies often use it rather than its sweeter cousin, citric acid, as the sourness is more intense. Salt and vinegar flavored potato chips also use it to produce a tart, vinegar-like flavor. Foods that contain large amounts of the acid often bear a warning, stating that eating large amounts of the product can cause soreness in the inside of the mouth.
Malic acid is also used as a supplement. The acid is involved in cell metabolism and the derivation of adenosine triphosphate (ATP), which plays a central role in the energy production rates of all cells in the body. It is used to treat fibromyalgia (FM), which causes intense pain in muscles and tendons. The acid aids in muscle performance and reduces muscle fatigue, and therefore assists in managing the pain caused by FM for many patients.
This sour acid also has the benefit of being an efficient metal chelator, which means it is able to securely bond with toxic metals, such as aluminum or lead, that are present in the body, limiting their abundance. Also, malic acid aids in dental hygiene, by acting as an antiseptic and encouraging saliva production. For this reason, it is found in many varieties of mouthwash.
In addition, this acid is also utilized by many skin care products. When applied to the skin, it tightens the pores, increasing the skin's smoothness and limiting the signs of any wrinkles or lines. Malic acid is considered safe for use, but can have several side effects. Skin rash, hives, or feeling a tightening in the chest can all be the result of excessive consumption of this compound.