Autoxidation of fatty materials in emulsions. I. Pro‐oxidant effect of histidine and trace metals on the oxidation of linoleate esters

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Abstract Aqueous emulsions of methyl or ethyl linoleate (sodium dodecylsulfate as emulsifier) together with such added components as 1‐histidine, metal chlorides, buffers, and acid or alkali, were oxidized in the dark with shaking in an oxygen atmosphere. Under optimum conditions (pH 6.5), the linoleate peroxide content, after 2 hr autoxidation at 20C, was increased more than 3‐fold by the addition of 1 ppm of ferrous or ferric ions, approximately 20‐fold by a 0.01 M concentration of histidine and more than 60‐fold by the addition of both histidine and ionic iron. The pro‐oxidative effect of other transition metal ions (Cu++, Co++, Cr+++, Mn++, and Ni++) also was investigated. None of these ions had a significant effect alone. Combined with 0.01 M histidine, only Mn++ increased peroxidation over that when when histidine alone was added. The pro‐oxidative action of histidine was retarded approximately 60% by 0.1 N acetate buffer and completely repressed by 0.05 M phosphate, nonionic emulsifiers, and low and high pH. The threshold concentration of histidine necessary for pro‐oxidative action was greater than 0.0001 M.

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