Analysis of organic acids

Abstract Organic acids are the organic compounds with the acidic properties, classified based on the number of carboxylic functions. In general, organic acids are weak acids. However, organic acids with phenol, enol, alcohol, and thiol groups are weaker than carboxylic acids. Organic acids vary in the number of hydroxy or carboxyl functional groups and carbon-carbon double bonds in their structures. The organic acids are categorized based on four characterizations: (1) the nature of carbon chain (aromatic, aliphatic, alicyclic, and heterocyclic); (2) saturation or unsaturation properties; (3) substituted or nonsubstituted features; and (4) the number of functional groups (mono, di- or tri-carboxylic). In the biological processes, organic acids are involved in numerous important pathways of metabolism and catabolism in animals and plants as the intermediate or final products, and play a main role in the tricarboxylic acid cycle or citric acid cycle (Krebs cycle), a vital pathway in eukaryotes and primary source of electrons donating to the mitochondrial respiratory membrane. Although these compounds are found in all organisms, plants have the unique ability to collect organic acids in cellular reactions. Organic acids affect fruits and vegetables' organoleptic properties such as color, flavor, and aroma. The current chapter will briefly introduce the organic acids in structures, physical, and chemical properties and discuss their Ethnopharmacology importance. Furthermore, the extraction techniques such as solid-liquid, ultrasound, microwave, accelerated liquid, supercritical fluid, and enzyme-assisted extraction will be reviewed. The purification techniques such as membrane separation, preparative high-performance liquid chromatography, counter-current chromatography, and thin layer chromatography are compared as well. As far as the identification and quantification techniques one would see gas chromatography, ion-exchange chromatography, capillary electrophoresis, high-performance liquid chromatography, nuclear magnetic resonance spectroscopy, and liquid chromatography-mass spectrometry. Finally, the levels of organic acids found in foods/plants and the effects of food processing on the phytochemicals are discussed.