On the antioxidant activities of the tocopherols II.—Influence of substrate, temperature and level of oxidation

The antioxidant activities of the tocopherols have been compared at 60° and at 37° in distilled methyl esters of cottonseed, linseed and cod liver oil fatty acids containing small additions of oxidised ester as “starter”. In the linoleate (cottonseed) system the γ‐ and δ‐compounds were the most and the α‐, ζ‐ and ϵ‐compounds the least effective in extending the induction period. In the polyunsaturated (linseed and cod liver oil) systems the γ‐ was still good, but the δ‐ was at the bottom of the series and the α‐ and ζ‐compounds near the top. Factors, in addition to the presence of polyunsaturated fatty esters in the substrate, which tended to favour a relatively high activity of the α‐compound were (a) comparison of activities at a low peroxide value, still within the induction period and (b) a not too high temperature of oxidation. Under suitable conditions α‐tocopherol could be shown to exert the highest and δ‐ the lowest in vitro antioxidant activity, in agreement with their known in vivo vitamin‐E potencies. The antioxidant activities of the tocopherols are considered in relation to their structure.