3-Methylbutanoic acid


3-Methylbutanoic acid, also known as β-methylbutyric acid or more commonly isovaleric acid, is an organic compound with the formula 2CHCH2CO2H. It is sometimes classified as a fatty acid. It is a colourless liquid that is sparingly soluble in water, but highly soluble in most common organic solvents. 3-methylbutanoic acid can be found in many common house items, such as cheese, soy milk, and apple juice. The compound occurs naturally.
Isovaleric acid has a strong pungent cheesy or sweaty smell, and its volatile esters are widely used in perfumery. It has been proposed that it is the anticonvulsant agent in valerian. It is a major component of the cause of intense foot odor, as it is produced by skin bacteria metabolizing leucine.
Isovaleric acid is seen as the primary cause of the flavors added to wine caused by Brettanomyces yeasts. Other compounds produced by Brettanomyces yeasts include 4-ethylphenol, 4-vinylphenol, and 4-ethylguaiacol. An excess of isovaleric acid in wine is generally seen as a defect, as it can smell sweaty, leathery, or like a barnyard, but in small amounts it can smell smokey, spicy, or medicinal. These phenomena may be prevented by killing any Brettanomyces yeasts, such as by sterile filtration, by the addition of relatively large quantities of sulfur dioxide and sometimes sorbic acid, by mixing in alcoholic spirit to give a fortified wine of sufficient strength to kill all yeast and bacteria, or by pasteurization. Isovaleric acid can also be found in beer, and, excepting some English–style ales, is usually considered a flaw. It can be produced by the oxidation of hop resins, or by Brettanomyces yeasts present.

Uses

Isovaleric acid has been used to synthesize β-hydroxyisovaleric acid – otherwise known as β-hydroxy β-methylbutyric acid – via microbial oxidation by the fungus Galactomyces reessii.