Palmitic acid, or hexadecanoic acid in IUPAC nomenclature, is the most common saturated fatty acid found in animals, plants and microorganisms. Its chemical formula is CH314COOH, and its C:D is 16:0. As its name indicates, it is a major component of the oil from the fruit of oil palms. Palmitic acid can also be found in meats, cheeses, butter, and other dairy products. Palmitates are the salts and esters of palmitic acid. The palmitate anion is the observed form of palmitic acid at physiologic pH. Aluminium salts of palmitic acid and naphthenic acid were combined during World War II to produce napalm. The word "napalm" is derived from the wordsnaphthenic acid and palmitic acid.
Occurrence and production
Palmitic acid was discovered by Edmond Frémy in 1840, in saponifiedpalm oil. This remains the primary industrial route for its production, with the triglycerides in palm oil being hydrolysed by high temperature water, and the resulting mixture fractionally distilled to give the pure product. Palmitic acid is naturally produced by a wide range of other plants and organisms, typically at low levels. It is naturally present in butter, cheese, milk, and meat, as well as cocoa butter, soybean oil, and sunflower oil. Karukas contain 44.90% palmitic acid. The cetylester of palmitic acid occurs in spermaceti.
Biochemistry
Excess carbohydrates in the body are converted to palmitic acid. Palmitic acid is the first fatty acid produced during fatty acid synthesis and is the precursor to longer fatty acids. As a consequence, palmitic acid is a major body component of animals. In humans, one analysis found it to make up 21–30% of human depot fat, and it is a major, but highly variable, lipid component of human breast milk. Palmitate negatively feeds back on acetyl-CoA carboxylase, which is responsible for converting acetyl-CoA to malonyl-CoA, which in turn is used to add to the growing acyl chain, thus preventing further palmitate generation. In biology, some proteins are modified by the addition of a palmitoyl group in a process known as palmitoylation. Palmitoylation is important for membrane localisation of many proteins.
Applications
Palmitic acid is used to produce soaps, cosmetics, and industrial mold release agents. These applications use sodium palmitate, which is commonly obtained by saponification of palm oil. To this end, palm oil, rendered from palm tree, is treated with sodium hydroxide, which causes hydrolysis of the ester groups, yielding glycerol and sodium palmitate. Because it is inexpensive and adds texture and "mouth feel" to processed foods, palmitic acid and its sodium salt find wide use in foodstuffs. Sodium palmitate is permitted as a natural additive in organic products. The aluminium salt is used as a thickening agent of napalm used in military actions. Hydrogenation of palmitic acid yields cetyl alcohol, which is used to produce detergents and cosmetics. Recently, a long-acting antipsychotic medication, paliperidone palmitate, used in the treatment of schizophrenia, has been synthesized using the oily palmitate ester as a long-acting release carrier medium when injected intramuscularly. The underlying method of drug delivery is similar to that used with decanoic acid to deliver long-acting depot medication, in particular, neuroleptics such as haloperidol decanoate.
Health effects
According to the World Health Organization, evidence is "convincing" that consumption of palmitic acid increases the risk of developing cardiovascular disease, based on studies indicating that it may increase LDL levels in the blood. Retinyl palmitate is a source of vitamin A added to low-fat milk to replace the vitamin content lost through the removal of milk fat. Palmitate is attached to the alcohol form of vitamin A, retinol, to make vitamin A stable in milk.
