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The acceleration of lipid oxidation by hemin was used to determine antioxidant activity and either fat or oil stability. The test system consisted of a fat or oil emulsion dispersed in phosphate buffer (pH 7.2). The temperature of the system was maintained at 45 ± 1 C. The antioxidant was added to the fat before emulsification. The rapid rate of oxygen uptake which occurred on the addition of hemin to the emulsion was measured with a Beckman oxygen analyzer and was recorded automatically. All fats and oils tested exhibited a typical induction period, which could be increased by the addition of an antioxidant. This increase in the induction period was related to antioxidant activity. The age and purity of the hemin solution, the concentration of hemin in the emulsion, the age and pH of the emulsion, the peroxide value of the fat, and the temperature affect the induction period and the rate of oxygen uptake. For a given set of conditions, the induction period was reproducible, although the rate of oxygen uptake was not. The activities of several antioxidants (butylated hydroxyanisole, propyl gallate,tertiary-butylhydroquinone, and Topanol) and synergists (ascorbic acid, citric acid, and ethylenediaminetetraacetic acid), determined by the hemin-catalyzed oxygen uptake method, are compared with those obtained by the active oxygen method.

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