Isovaleric acid, also known as3-methylbutanoic acid orβ-methylbutyric acid, is a branched-chainalkylcarboxylic acid with thechemical formula (CH3)2CHCH2CO2H. It is classified as ashort-chain fatty acid. Like other low-molecular-weight carboxylic acids, it has anunpleasant odor. The compound occurs naturally and can be found in many foods, such as cheese, soy milk, and apple juice.
3-Methylbutanoic acid is a minor constituent of the perennial flowering plantvalerian (Valeriana officinalis), from which it got itstrivial name isovaleric acid: anisomer ofvaleric acid which shares its unpleasant odor.[2] The dried root of this plant has been used medicinally since antiquity.[3][4] Their chemical identity was first investigated in the 19th century by oxidation of the components offusel alcohol, which includes the five-carbonamyl alcohols.[5]
Isovaleric acid has a strong pungent cheesy or sweaty smell,[11] but its volatileesters such asethyl isovalerate[12] have pleasant odors and are widely used in perfumery. It is also the primary flavor added to wine when made usingBrettanomyces yeasts.[13] Other compounds produced byBrettanomycesyeasts include4-ethylphenol,4-vinylphenol, and4-ethylguaiacol.[14] An excess of isovaleric acid in wine is generally seen as a defect,[14] as it can smell sweaty, leathery, or "like a barnyard", but in small amounts it can smell smokey, spicy, or medicinal.[13] These phenomena may be prevented by killing anyBrettanomyces yeasts, such as bysterile filtration, by the addition of relatively large quantities ofsulfur dioxide and sometimessorbic acid, by mixing in alcoholic spirit to give a fortified wine of sufficient strength to kill all yeast and bacteria, or bypasteurization. Isovaleric acid can also be found in beer, and, excepting some English–style ales, is usually considered a flaw.[15] It can be produced by the oxidation ofhop resins, or byBrettanomyces yeasts present.[15]
The compound's safety as a food additive was reviewed by anFAO andWHO panel, who concluded that there were no concerns at the likely levels of intake.[16]
Isovaleric acid is a major component of the cause of intensefoot odor, as it is produced by skin bacteria metabolizingleucine and in rare cases a condition calledisovaleric acidemia can lead to heightened levels of this metabolite.[19]
Anisovalerate or3-methylbutanoateion is (CH3)2CHCH2COO−, theconjugate base of the acid. It is the form found in biological systems atphysiological pH. An isovalerate or 3-methylbutanoate compound is asalt orester of the acid.
