The effect of α-tocopherol on the oxidation of mackerel oil

Mackerel oil is prone to autooxidation because it has a high content of polyunsaturated fatty acids. Antioxidants therefore have to be added to the oil to control oxidation during processing. The effect of 50, 100, 250 and 500 parts per million (ppm) concentrations of α-tocopherol on the oxidation of unrefined mackerel oil samples (recovered by solvent extraction), was investigated at 30, 4 and −40 °C over a period of 66 days by monitoring changes in peroxide values, conjugated diene content as well as levels of thiobarbituric acid reactive substances. There were significant differences (P < 0.05) between treated and control samples at all the temperatures investigated for all the α-tocopherol concentrations over the storage period. Higher concentrations of α-tocopherol, i.e., 250 and 500 ppm were less effective in controlling oxidation in the oils than lower α-tocopherol levels (50 and 100 ppm). Oxidation was minimal at low temperatures as inferred from the methods used to assess autooxidation. Treatment of mackerel oil with 50 or 100 ppm α-tocopherol at −40 °C produced the lowest oxidation over the 66-day period and was considered as adequate levels of incorporation in crude mackerel oil to minimize oxidation. There was no significant difference (P > 0.05) between the effects of 50 and 100 ppm of α-tocopherol after 66 days. Fifty ppm of α-tocopherol is therefore regarded as the preferred concentration for controlling oxidation of mackerel oil on the basis of cost and efficacy.