The effect of glazing and storage temperature on lipid oxidation and sensory properties of mackerel fillets was evaluated. A total of 288 fillets were stored for 6 months under stable temperature of -18 °C and unstable temperature, which involved six temperature fluctuation cycles from -18 to -5 °C each month. Glaze determination, chemical composition, thiobarbituric acid reactive substances examination and sensory evaluation of fillets were performed. Glazing and stable temperature conditions slowed down lipid oxidation in fillets compared to unglazed samples and samples stored under unstable freezing conditions. The thiobarbituric acid reactive substances increased slowly in glazed samples and a positive effect of stable conditions was found after two months and became obvious from the fifth month of storage. Sensory scores included evaluation of taste, aroma, texture, juiciness, and appearance corresponded to chemical results. Glazed fillets had the best scores in sensory evaluation and can be recommended for consumption; on the other hand, unglazed fillets stored under unstable temperature could not be consumed because of rancidity. This is the first similar study in mackerel when unstable temperature conditions are considered as a factor increasing lipid oxidation. Prevention of temperature fluctuation during storage is important to keep the quality of the frozen fillets.
Lipid oxidation, sensory properties, thiobarbituric acid reactive substancesAlthough freezing is an effective method of preserving foods, some deterioration in frozen food quality occurs during storage. The extent of quality loss depends on many factors, including the rate of freezing and thawing, storage temperature, temperature fluctuation, transportation, retail display and consumption (Boonsumrej et al. 2007). In this circumstance, factors such as mild temperature abuse or storing foods at very low temperatures may have varying effects on the quality, depending on the product.In fatty species of fish such as herring (Clupeidae), anchovy (Engraulidae), mackerel (Scombridae), and salmon (Salmonidae), the most serious cause of deterioration is oxidation. Fish lipids contain high levels of polyunsaturated fatty acids, which are susceptible to attack by molecular oxygen, when lipid oxidation typically results in formation of aldehydes, alkyl radicals and semialdehydes (Chen et al. 2008). The chemical tests for detecting oxidation and quantifying the extent of oxidation are based upon these changes. Thus, malondialdehyde (MDA), a major degradation product of lipid oxidation is used as a marker for assessing the extent of lipid oxidation and the most frequently method used for MDA determination is estimation of thiobarbituric acid reactive substances (TBARS) (Cordis et al. 1995). However, TBARS values go up during the initial phase of propagation stage and down in the termination stage of oxidation, the lipid oxidation leads also to objectionable changes of flavours, therefore sensory tests provided useful information related to qua...