This article is a review of the fundamental chemistry of the tocopherols and tocotrienols relevant to their antioxidant action. Despite the general agreement that α-tocopherol is the most efficient antioxidant and vitamin E homologuein vivo, there was always a considerable discrepancy in its “absolute” and “relative” antioxidant effectivenessin vitro, especially when compared to γ-tocopherol. Many chemical, physical, biochemical, physicochemical, and other factors seem responsible for the observed discrepancy between the relative antioxidant potencies of the tocopherolsin vivo andin vitro. This paper aims at highlighting some possible reasons for the observed differences between the tocopherols (α-, β-, γ-, and δ-) in relation to their interactions with the important chemical species involved in lipid peroxidation, specifically trace metal ions, singlet oxygen, nitrogen oxides, and antioxidant synergists. Although literature reports related to the chemistry of the tocotrienols are quite meager, they also were included in the discussion in virtue of their structural and functional resemblance to the tocopherols.

The chemistry and antioxidant properties of tocopherols and tocotrienols

Scope of the Paper This paper cites the paradoxical actions of antioxidants in processed foods and in living biological systems. Essentially, it is a recognition of patterns of contradictory behavior. Limitations of space prevent detailed treatment of the paradoxes, their mechanistic basis, or citation of any more than one or two illustrative references. It is hoped that these will lead the interested reader to further substantiation of the paradoxes cited.

Paradoxical behavior of antioxidants in food and biological systems.

An evaluation of thiobarbituric acid (TBA) as an agent for the measurement of fat oxidation was made by the application of several empirical procedures to animal and vegetable fats. An extraction procedure was used for removing the products of oxidation. The reaction with TBA was conducted in a boiling water bath to produce a red color, which was then estimated spectrophotometrically. Fats stored at −20, 0, 72, and 100°F. (−29, −18, 22, and 38°C.) and fats oxidized by the active oxygen method (A.O.M.) and by ultraviolet irradiation were examined. It was found that the TBA test might be of value in following the course of oxidation of cottonseed oil and soybean oil in the A.O.M. apparatus. Higher TBA values were obtained for soybean oil than cottonseed oil at comparable peroxide values. This is of interest because of the greater tendency of soybean oil to develop oxidized flavors. The volatile reaction products of oxidation were collected in toluene, and a comparison of the TBA values at comparable peroxide values of lard, cottonseed and soybean oils showed that the soybean oil volatiles developed the greatest intensity of color.

The use of thiobarbituric acid as a measure of fat oxidation

The antioxidant activities of the seven tocopherols and of the unmethylated parent compound (tocol) have been compared in several systems



The three tocopherols unsubstituted in the 5-position (δ, γ and η) were more effective than the other four in protecting carotene in mineral oil solution at 75°



In lard esters at 90° and in methyl linoleate at 50° δ, γ, η and β were the most, and ϵ, ζ and α the least, effective, the precise order depending on the conditions and concentrations used the tocopherols were much less effective in protecting lard esters exposed to light, δ being the best of the series

Relative antioxidant activities of the seven tocopherols

This review covers the literature on sesamin, sesamolin and related compounds published since 1951. The topics reviewed include structural con-siderations, natural occurrence, influence of oil processing, analytical methods, isolation proce-dures and commercial preparations, various bio-logical effects and stability questions. Recent developments in pyrethrum synergists are discussed at length, since they owe so much to the discovery of the synergistic activities of sesamin and sesamolin.

Recent research on sesamin, sesamolin, and related compounds

Thirteen compounds have been intercompared with respect to their antioxidant activity in concentrations of 0.01, 0.05, and 0.10% in edible cottonseed oil, the same oil hydrogenated to shortening consistency, and in lard which is essentially free of naturally occurring antioxidants. None of the compounds exhibited significant antioxidant activity in the cottonseed oils, when use in a concentration of 0.01%, but they were effective in stabilizing lard under these conditions. Propyl gallate was the most effective of the compounds tested for the vegetable fats.

W. G. Bickford

Papers

A comparative evaluation of several antioxidants in edible fats