Specifies an enzymic method, which is not applicable to fats and oils containing polyunsaturated fatty acids of the omega-8 and omega-9 series or containing branched chain fatty acids. The method consists in saponifying of a test portion at ambient temperature followed by liberation of the fatty acids; enzymic oxidation of the fatty acids; measurement, at the wavelength of maximum absorbance (about 235 nm) of the absorbance due to these oxidized acids, while compensating for the absorbance due to any dienoic conjugated acids initially present in the sample.