The major provitamin carotenoid, B-carotene, has similar solvent properties. Saponification and direct solvent extraction are commonly used to extract retinoids and carotenoids from biological samples.
When applicable, direct solvent extraction is preferable to saponification because of time, lower solvent costs, and a better ability to avoid formation of artifacts in the extract.
One of the richest sources of vitamin A is liver tissue, in particular the liver oils of marine fish and mammals. The esters can be directly isolated from these oils by molecular distillation at very low pressure, a procedure that has been used extensively for the commercial preparation of vitamin A-rich oils.
Alternatively, vitamin A might be directly extracted with chloroform or with some other solvent combination, such as hexane together with ethanol, followed by purification of vitamin A by chromatography means.
The solvent system used for direct solvent extraction must be applicable of penetrating tissues and breaking lipoprotein bonds to free the analyst. Other than hexane the useful solvents include diethyl ether, ethyl acetate and various solvent mixtures.
To hydrolyze esters, not only of vitamin A and carotenoid but also of triglycerides and other lipids, saponification with KOH is commonly used, followed by extraction with organic solvents.
Retinol or its esters can be readily crystallized at low temperature from a variety of organic solvents, including ethyl formate, propylene oxide, and methanol.
Extraction of Vitamin A
