Oxidation of Methyl Linoleate and the Influence of Antioxdants. IV. On the Antioxidant Action of α-Tocopherol and Synergism of Organic Acids

Abstract

In a series of the studies, the antioxidant effect of D, L-α-tocopherol and the synergistic effects of some kinds of organic acids on the oxidation of methyl linoleate (ML) with oxygen were reported in this paper. Samples and experimental conditions were same as those described in the previous paper. Oxygen was passed through purified ML with or without the antioxidant and the synergists, then the samples obtained were estimated for peroxide value. Antioxidant effect of α-tocopherol on the oxidation at 105°was shown little in the absence of the synergist, but was remarkable in the presence of ascorbic acid or citric acid. The effect of α-tocopherol on the oxidation at 70°was clearly observed even without any synergist, but the addition of it increased markedly the antioxidant offect of α-tocopherol. The effect of α-tocopherol was compared with that of butyl hydroxy anisol (BHA), which had been reported in the previous paper. It was shown that the effect of BHA was more active than that of α-tocopherol ; even a half equivalent of BHA was more effective than α-tocopherol on the oxidation at 70°. Sixteen kinds of organic acids and esters were examined for the synergistic effect with α-tocopherol and eight of them were found to be effective in preventing oxidatien of methyl linoleate ; D, L-malic, L-tartaric, oxaloacetic, malonic, citric, L-ascorbic, and D, L-gliceric acids and diethyl malate were effective ; succinic (weak +), tartronic, propionic, lactic, β-hydroxybutyric, and pyruvic acids, gluconolactone, and triethyl citrate were ineffective. The mechanism of the synergistic action of these organic acids seemed to be complicated, but the synergist was assumed to act as a hydrogen donor to α-tocopherol (or its oxidation products).