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.