Acid-catalyzed isomerization of fucosterol and Δ5-avenasterol

This work shows that fucosterol, Delta(5)-avenasterol, and similar ethylidene-side chain sterols can undergo acid-catalyzed isomerization to give a mixture of five isomers. Four isomers formed from fucosterol were analyzed, using gas chromatography-mass spectrometry, and were characterized as Delta(5)-avenasterol, two Delta(5,23)-stigmastadienols, and Delta(5,24(25))-stigmastadienol. When the unsaponifiables fraction from oat oil was subjected to acid hydrolysis, the two Delta(5,23)-stigmastadienol isomers and Delta(5,24(25))-stigmastadienol were detected while fucosterol coeluted with sitosterol. Interisomerization of ethylidene-side chain sterols represents a limitation to the use of the acid hydrolysis method in the determination of sterols in food and other plant materials rich in these sterols, e.g., oat lipids.