Butyric acid

Butyric acid (from Ancient Greek: βούτῡρον, meaning 'butter'), also known under the systematic name butanoic acid, is a carboxylic acid with the structural formula CH3CH2CH2-COOH. Salts and esters of butyric acid are known as butyrates or butanoates. Butyric acid is found in animal fat and plant oils, bovine milk, breast milk, butter, parmesan cheese, and as a product of anaerobic fermentation (including in the colon and as body odor). Butyric acid has a taste somewhat like butter and an unpleasant odor. Mammals with good scent detection abilities, such as dogs, can detect it at 10 parts per billion, whereas humans can detect it only in concentrations above 10 parts per million. In food manufacturing, it is used as a flavoring agent. Butyric acid is a biologically active compound in humans. Butyric acid is one of two primary endogenous agonists of human hydroxycarboxylic acid receptor 2 (HCA2), a Gi/o-coupled G protein-coupled receptor. Butyric acid is a fatty acid occurring in the form of esters in animal fats. The triglyceride of butyric acid makes up 3–4% of butter. When butter goes rancid, butyric acid is liberated from the glyceride by hydrolysis, leading to the unpleasant odor. It is one of the fatty acid subgroup called short-chain fatty acids. Butyric acid is a medium-strong acid that reacts with bases and affects many metals. The acid is an oily, colorless liquid that is easily soluble in water, ethanol, and ether, and can be separated from an aqueous phase by saturation with salts such as calcium chloride. It is oxidized to carbon dioxide and acetic acid using potassium dichromate and sulfuric acid, while alkaline potassium permanganate oxidizes it to carbon dioxide. The calcium salt, Ca(C4H7O2)2·H2O, is less soluble in hot water than in cold. Butyric acid has a structural isomer called isobutyric acid (2-methylpropanoic acid).