The biological activity of the tocopherols and tocotrienols has been re-examined by the rat resorption-gestation test. The following values have been obtained (with d,l-alpha-tocopheryl acetate = 100%): d-alpha-tocopherol 80%; d,l-alpha-tocopherol 59%; d-alpha-tocopheryl acetate 136%; d-alpha-tocotrienol 13%; d-beta-tocopherol 45%; d-beta-tocotrienol 4%; d-gamma-tocopherol 13%; d-delta-tocopherol less than 0.4%. The possibility of alpha- and gamma-tocopherol being synergists has been tested, but no significant effect was found. The antioxidants BHT and ethoxyquin were without effect on the utilization of alpha-tocopherol by the rat. After chemical determination of the tocopherols and tocotrienols in foods and mixed feeds, these biological activities were used to calculate the vitamin E activity. For two samples of margarine and two samples of mixed feed, the calculated value of the vitamin E activity after chemical determination of the tocopherols and tocotrienols was compared with the value found by direct bioassay, and reasonably good agreement was found. The authors suggest that determination of vitamin E in foods and feeds as a rule should be carried out as a chemical determination of the individual tocopherols and tocotrienols followed by a calculation of the vitamin E activity from the biological activity of the tocopherols and tocotrienols.
