The loss of water- and lipid-soluble antioxidants of mackerel light and dark muscle was determined as a function of time of storage on ice to provide clues as to mechanisms of oxidation and to assess the use of antioxidants to measure and predict quality. Glutathione and ascorbate decreased faster initially than α-tocopherol and ubiquinone in both light and dark muscle of mackerel; in dark muscle, the rate of loss of ubiquinol was comparable to the loss of the water-soluble antioxidants. Antioxidants decreased more rapidly initially in dark muscle than in light muscle. Rates of sensory quality loss in the light and dark muscles were similar except that initial loss of quality in the dark muscle was greater than that in the light. Regression equations showed good relationships of tocopherol, ubiquinone-10, and TBARS in light and dark muscle with storage time. Ascorbate and glutathione gave the best correlation values with sensory scores for light muscle, while a good relationship was seen in dark muscle between sensory score and reduced or oxidized CoQ, ascorbate, and glutathione. The kinetic data suggest an important role of mitochondria in lipid oxidation in mackerel dark muscle. Keywords: Mackerel; antioxidants; ascorbate; glutathione; α-tocopherol; coenzyme Q; stability

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Minced mackerel muscle was less stable at -20 °C than minced bluefish muscle as judged by odor evaluation but not by production of TBA-reactive substances. Minced mackerel muscle lost total glutathione faster than minced bluefish muscle at both -20 and 2 °C. Loss of glutathione was also more rapid in mackerel fillets than in bluefish fillets, but the differences were less. Sensory scores declined in both species after about two-thirds of the glutathione was lost. Neither soluble selenium nor glutathione peroxidase, oxidized glutathione reductase, or glutathione transferase activities appeared likely to account for the differences observed in glutathione losses. In a model system of washed, minced mackerel light muscle, glutathione/glutathione peroxidase was an effective antioxidant against lipid oxidation induced by an exogenous free radical-generating system. It seems possible that glutathione protected the fish muscle against quality loss in the early stages of storage.

Ubiquinol, the reduced form of coenzyme Q, is known as a lipid antioxidant. Its fully oxidized form, ubiquinone, would theoretically not have this activity. However, we report that ubiquinone‐10, the oxidized form of coenzyme Q, demonstrated antioxidant activity in model studies against a lipid‐soluble free radical generator, 2,2′‐azobis(2,4‐dimethylvaleronitrile). This was demonstrated at both 1:100 and 1:1,000 ratios of ubiquinone‐10 to lipid (for both methyl linoleate and methyl linolenate). Ubiquinone‐10 should therefore not be discounted as a possible antioxidant in more complex systems such as food. PRACTICAL APPLICATIONS Coenzyme Q (ubiquinol/ubiquinone) is an important component of electron transport in biological tissues and is also classified as a potent antioxidant. It is generally believed that the form that is active as an antioxidant is the reduced ubiquinol. In evaluating the loss of antioxidants in mackerel light and dark muscle tissues, it was observed that the oxidized form, ubiquinone, comprised over 87% of the total coenzyme Q in light muscle and over 93% in dark muscle and this observation did not change under anaerobic conditions. This study was done to determine if the oxidized form of coenzyme Q, ubiquinone, was capable of acting as an antioxidant. In this study, it is shown that it can function in this manner.