Lipid, compound unsaponifiable

Saponification of the extracts is generally desirable to remove unwanted lipid materials. However, this step is omitted in the isolation of carotenol esters, since these are hydrolyzed by this procedure. It is also omitted in the isolation of carotenoids such as fucoxanthin and peridinin, which are alkali-labile. If acetone has been used in the initial extraction, it is essential that all traces be removed before saponification. The general procedure used involves dissolving the total lipid fraction in an alcoholic (ethanol or methanol) solution of potassium hydroxide. The mixture is then either heated for a short period of time while kept in the dark, or left in the dark at room temperature for 12-16 h. There has been considerable discussion of the merits of these two procedures. Which method is used is dependent on the nature of the samples being analyzed and the requirements of the analysis (Davies, 1976 Liaaen-Jensen, 1971). After saponification, water is added, and neutral lipids (the unsaponifiable fraction) are extracted with diethyl ether or hexane. Acidic carotenoids remain in the alkaline phase and are extracted with diethyl ether or hexane after acidification with acetic acid. The unsaponifiable fraction usually contains sterols as well as carotenoids. If desired, sterol contaminants can be removed by precipitation from cold (- 10°C) petroleum ether or by precipitation of these compounds as their digitonides. 

Sterols. These compounds are found in the unsaponifiable fraction of milk lipids and consist mostly of cholesterol with some lanosterol. Methods for the determination of unsaponifiables using dry saponifica-... 

In practice, the non-volatile lipophihc compounds that accompany true lipids in both natural and manufactured products are also classified as lipids. They are termed compounds accompanying lipids (formerly called Kpoids) in food chemistry, and unsaponifiable lipophilic substances in food analysis. Their chemical structure is different and often these compounds do not even contain bound fatty acids. This group includes a large number of lipophilic compounds, for example some terpenoids, especially... 

Other unsaponifiable compounds similar to cholesterol have been found in the lipids of a variety of plant and animal sources. The collective name sterols has been adopted for all crystalline unsaponifiable alcohols with properties resembling those of cholesterol. In general, these... 

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