Synthetic preparations of vitamin E are mixtures of all eight possible stereoisomers.
Of the different forms available (alpha, beta, gamma and delta), alpha-tocopherol is the most biologically active form. The biological activity of 1 mg of dl-alpha-tocopheryl acetate (also called all-rac-alpha-tocopheryl acetate) is equivalent to one IU of vitamin E.
Tocopherols are light oils at room temperature. They are good quenchers of free radicals and thus serve as antioxidants. They are, however, easily oxidized and can be destroyed by peroxides, ozone, and permanganate in a process catalyzed by light and accelerated by polyunsaturated fatty acids and metal salts.
Tocopheryl esters, by virtue of the blocking of the C-6 hydroxyl group, are very stable in air and are, therefore, the forms of choice as food/feed supplements. Tocopheryl esters do not have any antioxidative properties until hydrolyzed in the intestine to free tocopherol.