The relationship between dietary phytosterols and the sterols of wild and cultivated oysters

Wild oysters (Crassostrea virginica) contained cholesterol, 24‐methyl‐cholesta‐5, 22‐dienol, 24‐methylenecholesterol, 22‐dehydrocholesterol, 24‐methylcholesterol, 24‐ethylcholesterol, 24‐norcholesta‐5, 22‐dienol, 24‐ethylcholesta‐5, 22‐dienol and fucosterol. The same species was cultivated on a defined diet ofThalassiosira pseudonana andIsochrysis sp. The dietary algae were cultured and their sterol compositions were analyzed by gas chromatography and mass spectroscopy.T. pseudonana andIsochrysis sp. had 24‐methylenecholesterol and 24‐methyl‐cholesta‐5, 22‐dienol as their major sterols. The sterol composition of the cultivated oysters revealed the predominance of cholesterol (19%), 24‐methyl‐cholesta‐5, 22‐dienol (21%) and 24‐methylenecholesterol (46%). Therefore, oysters must be able to bioconvert phytosterols to cholesterol, concentrate dietary cholesterol, or synthesize cholesterol de novo.