The antioxidant effectiveness of two different families of phenolic compounds, hydroxycinnamic acids and catechins, added as a power (0.001% w/w) to chilled minced horse mackerel muscle was evaluated. Caffeic acid, chlorogenic acid, o-coumaric acid, and ferulic acid were selected as hydroxycinnamic acids with similar molecular structures. Commercial catechins with different numbers of hydroxylic groups, including catechin, gallocatechin, catechin gallate, and gallocatechin gallate, were also tested. The effectiveness found was individually discussed for each family as a function of the molecular structure. The capacity of hydroxycinnamic acids for donating electrons seems to play the most significant role for retarding the development of rancidity in fish muscle. Conversely, the properties related to the ability for chelating metals and the distribution between oily and aqueous phases were not correlated with the inhibitory activities. Among hydroxycinnamic acids, the results highlighted the potent antioxidant activity of 10 ppm caffeic acid in inhibiting lipid oxidation in fish muscle. Its antioxidant efficacy was similar to that of propyl gallate. Among catechins, catechin showed the highest antioxidant activity. There was an increment of efficacy in fish muscle using concentrations ranging between 10 and 100 ppm of both caffeic acid and catechin.

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The development of rancidity and its effect on quality loss was studied in frozen horse mackerel (Trachurus trachurus). For that, two different kinds of fish products (whole fish and fillets) were stored at a commercial frozen temperature (-20ºC) for up to 12 months and were compared to samples stored at a much low temperature (-80ºC).Analyses included: lipid hydrolysis (free fatty acid formation) and oxidation (peroxide value, thiobarbituric acid index, fluorescent compounds formation), loss in endogenous antioxidant (alpha-tocopherol), proteins changes (electrophoretic analysis of sarcoplasmic and SDS soluble fractions) and sensory analysis (skin, eyes, gills, flesh odor, consistency, flesh appearance). According to biochemical indices, fillets stored at -20ºC showed susceptibility to rancidity development, leading to a shelf life of 1 month, while whole fish at the same temperature were still edible at month 5. The employment of a low temperature (-80ºC) inhibited the rancidity development leading to good quality (whole fish) and fair quality (fillets) fish products at the end of the experiment. The application of protective treatments specially designed to prevent lipid oxidation is encouraged when commercializing this species in the frozen state.Running Title: Quality and frozen horse mackerel 2In the last few decades, marine foods have captured a great attention from consumer because of a positive role on human health and nutrition (1,2). Marine species are known to give rise to a wide range of products of great economic importance in many countries. However, the fishing industry is actually suffering from dwindling stocks of traditional species as a result of drastic changes in their availability. As a result, fish technologists and fish trade have turned their attention to some unconventional sources of raw material (3,4).One such species is horse mackerel (Trachurus trachurus), a medium fat species, abundant in the Northeast Atlantic (5). Efforts have been done to utilize it in the manufacture of several products such as smoked (6), canned (7), chilled (8) and frozen (9) fish.Freezing and frozen storage have largely been employed to retain fish sensory and nutritional properties (10,11). However, marine species have shown a highly unsaturated lipid composition and an important presence of prooxidant molecules that facilitate the development of rancidity (12,13). Under frozen conditions, lipid oxidation compounds are produced and have shown to interact with proteins leading to protein denaturation (14), nutritional losses (15) and modification of electrophoretic profiles of proteins (16), while endogenous antioxidant systems have shown to be partially lost (17).The present work concerns horse mackerel (Trachurus trachurus) and its commercialization as a frozen product. For that, two different kinds of fish products (whole fish and fillets) were kept frozen at a commercial temperature (-20ºC) and compared to the corresponding controls held at -80ºC. Analyses included lipid hydrolysis and oxidation...