Non-saponifiable compounds

Lipids are substances of biological origin that are soluble in non-polar solvents. There are saponifiable lipids, such as acylglycerols (fats and oils), waxes and phospholipids, as well as non-saponifiable compounds, principally steroids. 

Parcerisa, J., Casals, I., Boatella, J., Codony, R., and Rafecas, M. 2000. Analysis of Olive and Hazelnut Oil Mixtures by High-Performance Liquid Chromatography — Atmospheric Pressure Chemical Ionisation Mass Spectrometry of Triacyglycerols and Gas-Liquid Chromatography of Non-Saponifiable Compounds (Tocopherols and Sterols). J. Chromatogr. A. 881 149-158. 

The term lipid includes all compounds that release fatty acids on digestion, so that this definition is more extensive than that of fat. Compounds which are insoluble in water, soluble in organic solvents but not derived from fatty acids have been termed non-saponifiable lipids. They include steroids, terpenes and ubiquinone. 

Naturally occurring lipid mixtures have a composition of such extreme complexity that the analysis by chemical methods of a group of these substances or the determination of a single compound in such mixtures, appears hopeless. Up to about ten years ago, lipid mixtures were characterised by totals like acid-, saponification-, iodine-, thio-cyanogen- and diene- numbers . The determination of the amount of non-saponifiable matter after alkaline hydrolysis was a standard method in the analysis of fats. Phospholipids and sulpholipids were quantitatively determined as inorganic phosphate and sulphate after combustion. These methods were supplemented by detection of subsidiary fat constituents like lipochromes, sterols and resin acids, with the help of colour reactions. 

Alkaline hydrolysis ( saponification ) of fatty materials yields the water-soluble alkali salts of the fatty acids in these lipids, plus non-saponifiable neutral compounds such as hydrocarbons and alcohols. The non-saponifiable matter is extracted from the alkaline aqueous-alcoholic phase with non-polar solvents. The fatty acids are then liberated by acidification and likewise extracted with organic solvents. 

Lipoids as a type are non-saponifiable, although some of the sterols may occur as esters with aliphatic acids. A systematic classification of the lipoids is unsatisfactory, since the only common property of these compounds is the physical one of solubility in certain organic solvents. Examples of biological lipoids occur in the essential or volatile oils of plants and the fat-soluble pigments (lipochromes) of plants and animals. In addition, some of the vitamins and the hormones belong to the lipoid type, in that they are fat-soluble. 

The efficiency of the human digestive process in health is such that about 96 per cent, of the total mixed dietary is made available for absorption into the portal and lymphatic systems. Colloids have been converted into diffusible solutes, insoluble fats have been emulsified and saponified, compound saccharides have been changed into utiUsable monosaccharides, and foreign proteins have been rendered non-toxic by being hydrolysed into non-specific mixtures of amino acids. 

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