Cis/trans isomers of tocotrienols - occurrence and bioavailability

In nature tocotrienols (compounds of vitamin E) have only been found in the 2R,3'trans,7'trans (R, trans-trans) configuration whereas synthetic tocotr ienols often represent a mixture of cis and trans side chain isomers. In th is study tocotrienols were isolated from samples (egg yolk, palm oil, and e we's milk) by extraction of the unsaponifiable matter and subsequent semi-p reparative high-performance liquid chromatography (HPLC). A recently develo ped HPLC method [two series-connected columns ET 200/4 NUCLEO-DEX beta-PM ( 200x4mm ID, permethylated beta-cyclodextrin phase; Macherey-Nagel, Duren, G ermany), acetonitrile/water eluent (58:42 by vol.), fluorescence detection at an emission wavelength of 330 nm (excitation wavelength = 295 nm)] was u sed to separate the isolated tocotrienols into the four potential cis/trans side chain isomers. Commercially available, synthetic alpha-tocotrienol wa s orally administered to a laying hen. In the egg yolk all our alpha-tocotr ienol geometrical isomers could be determined, thus demonstrating the bioav ailability. Furthermore, no cis/trans isomers of gamma-tocotrienol from har dened palm oil (melting point 46 degrees C) could be detected, i.e. the hyd rogenation process during oil hardening evidently caused no isomerization o f gamma-tocotrienol. Finally, it is shown that ewe's milk does not contain a detectable amount of cis/trans alpha-tocotrienol isomers, which might der ive from biohydrogenation during microbial metabolism in the rumen.