In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, from 4 to 28. Fatty acids are a major component of the lipids in some species such as microalgae but in some other organisms are not found in their standalone form, but instead exist as three main classes of esters: triglycerides, phospholipids, and cholesteryl esters. In any of these forms, fatty acids are both important dietary sources of fuel for animals and important structural components for cells.
In nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such compounds, most commonly those that occur in living beings or in food.
Essential fatty acids, or EFAs, are fatty acids that humans and other animals must ingest because the body requires them for good health, but cannot synthesize them.
A saturated fat is a type of fat in which the fatty acid chains have all single bonds. A fat known as a glyceride is made of two kinds of smaller molecules: a short glycerol backbone and fatty acids that each contain a long linear or branched chain of carbon (C) atoms. Along the chain, some carbon atoms are linked by single bonds (-C-C-) and others are linked by double bonds (-C=C-). A double bond along the carbon chain can react with a pair of hydrogen atoms to change into a single -C-C- bond, with each H atom now bonded to one of the two C atoms. Glyceride fats without any carbon chain double bonds are called saturated because they are "saturated with" hydrogen atoms, having no double bonds available to react with more hydrogen.
Stearic acid is a saturated fatty acid with an 18-carbon chain. The IUPAC name is octadecanoic acid. It is a soft waxy solid with the formula CH3(CH2)16CO2H. The triglyceride derived from three molecules of stearic acid is called stearin. Stearic acid is a prevalent fatty-acid in nature, found in many animal and vegetable fats, but is usually higher in animal fat than vegetable fat. It has a melting point of 69.4 °C and a pKa of 4.50.
Palmitic acid is a fatty acid with a 16-carbon chain. It is the most common saturated fatty acid found in animals, plants and microorganisms. Its chemical formula is CH3(CH2)14COOH, and its C:D ratio is 16:0. It is a major component of palm oil from the fruit of Elaeis guineensis, making up to 44% of total fats. Meats, cheeses, butter, and other dairy products also contain palmitic acid, amounting to 50–60% of total fats.
Oleic acid is a fatty acid that occurs naturally in various animal and vegetable fats and oils. It is an odorless, colorless oil, although commercial samples may be yellowish. In chemical terms, oleic acid is classified as a monounsaturated omega-9 fatty acid, abbreviated with a lipid number of 18:1 cis-9, and a main product of Δ9-desaturase. It has the formula CH3−(CH2)7−CH=CH−(CH2)7−COOH. The name derives from the Latin word oleum, which means oil. It is the most common fatty acid in nature. The salts and esters of oleic acid are called oleates. It is a common component of oils, and thus occurs in many types of food, as well as in soap.
Isobutyric acid, also known as 2-methylpropanoic acid or isobutanoic acid, is a carboxylic acid with structural formula (CH3)2CHCOOH. It is an isomer of butyric acid. It is classified as a short-chain fatty acid. Deprotonation or esterification gives derivatives called isobutyrates.
Capric acid, also known as decanoic acid or decylic acid, is a saturated fatty acid, medium-chain fatty acid (MCFA), and carboxylic acid. Its formula is CH3(CH2)8COOH. Salts and esters of decanoic acid are called caprates or decanoates. The term capric acid is derived from the Latin "caper / capra" (goat) because the sweaty, unpleasant smell of the compound is reminiscent of goats.
Caprylic acid, also known under the systematic name octanoic acid or C8 Acid, is a saturated fatty acid, medium-chain fatty acid (MCFA). It has the structural formula H3C−(CH2)6−COOH, and is a colorless oily liquid that is minimally soluble in water with a slightly unpleasant rancid-like smell and taste. Salts and esters of octanoic acid are known as octanoates or caprylates. It is a common industrial chemical, which is produced by oxidation of the C8 aldehyde. Its compounds are found naturally in the milk of various mammals and as a minor constituent of coconut oil and palm kernel oil.
3-Methylbutanoic acid, also known as β-methylbutyric acid or more commonly isovaleric acid, is a branched-chain alkyl carboxylic acid with the chemical formula (CH3)2CHCH2CO2H. It is classified as a short-chain fatty acid. Like other low-molecular-weight carboxylic acids, it has an unpleasant odor. The compound occurs naturally and can be found in many foods, such as cheese, soy milk, and apple juice.
Pelargonic acid, also called nonanoic acid, is an organic compound with structural formula CH3(CH2)7CO2H. It is a nine-carbon fatty acid. Nonanoic acid is a colorless oily liquid with an unpleasant, rancid odor. It is nearly insoluble in water, but very soluble in organic solvents. The esters and salts of pelargonic acid are called pelargonates or nonanoates.
Elaidic acid is a chemical compound with the formula C
18H
34O
2, specifically the fatty acid with structural formula HOOC−(CH2)7−CH=CH−(CH2)7−CH3, with the double bond in trans configuration. It is a colorless oily solid. Its salts and esters are called elaidates.
Medium-chain triglycerides (MCTs) are triglycerides with two or three fatty acids having an aliphatic tail of 6–12 carbon atoms, i.e. medium-chain fatty acids (MCFAs). Rich food sources for commercial extraction of MCTs include palm kernel oil and coconut oil.
Vaccenic acid is a naturally occurring trans fatty acid and an omega-7 fatty acid. It is the predominant kind of trans-fatty acid found in human milk, in the fat of ruminants, and in dairy products such as milk, butter, and yogurt. Trans fat in human milk may depend on trans fat content in food.
Margaric acid, or heptadecanoic acid, is a saturated fatty acid. Its molecular formula is CH3(CH2)15CO2H. Classified as an odd-chain fatty acid, it occurs as a trace component of the fat and milkfat of ruminants. Salts and esters of margaric acid are called heptadecanoates.
Tridecylic acid, or tridecanoic acid, is the organic compound with the formula CH3(CH2)11CO2H. It is a 13-carbon saturated fatty acid. It is a white solid.
Nonadecylic acid, or nonadecanoic acid, is a 19-carbon saturated fatty acid with the chemical formula CH3(CH2)17COOH. It forms salts called nonadecylates. Nonadecylic acid can be found in fats and vegetable oils, although it is rare.
Heneicosylic acid, or heneicosanoic acid, is the organic compound with the formula CH3(CH2)19CO2H. It is the straight-chain 21-carbon saturated fatty acid. It is a colorless solid.
Odd-chain fatty acids are those fatty acids that contain an odd number of carbon atoms. In addition to being classified according to their saturation or unsaturation, fatty acids are also classified according to their odd or even numbers of constituent carbon atoms. With respect to natural abundance, most fatty acids are even chain, e.g. palmitic (C16) and stearic (C18). In terms of physical properties, odd and even fatty acids are similar, generally being colorless, soluble in alcohols, and often somewhat oily. The odd-chain fatty acids are biosynthesized and metabolized slightly differently from the even-chained relatives. In addition to the usual C12-C22 long chain fatty acids, some very long chain fatty acids (VLCFAs) are also known. Some of these VLCFAs are also of the odd-chain variety.
