Isolation of Vitamin A
In nature vitamin A is largely found as an ester and consequently, is highly soluble in organic solvents but not in aqueous solutions.
The major pro vitamin carotenoid, B-carotene, has similar solvent properties. One of the richest sources of vitamin A is liver tissue, in particular the liver oils of marine fish and mammals.
The ester 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 vitamins 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 chromatographic means.
To hydrolyze esters not only of vitamin A and carotenoids 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 format, propylene oxide, and methanol.
Isolation of Vitamin A
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