Quality loss related to rancidity development during frozen storage of horse mackerel (<Emphasis Type="Italic">Trachurus trachurus</Emphasis>)

The development of rancidity and its effect on quality loss were studied in frozen horse mackerel (Trachurus trachurus). Two different kinds of fish products (whole fish and fillets) were stored at a commercial freezer temperature (−20°C) for up to 12 mon and were compared to samples stored at a much lower temperature (−80°C). Analyses included: lipid hydrolysis (FFA formation) and oxidation (PV, thiobarbituric acid index, fluorescent compound formation), loss of endogenous antioxidant (α-tocopherol), protein 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 −20°C showed susceptibility to rancidity development, leading to a shelf life of 1 mon, whereas whole fish at the same temperature were still edible at month 5. The use of a low temperature (−80°C) inhibited rancidity development, leading to good-quality (whole fish) and fairquality (fillets) fish products at the end of the experiment. The application of protective treatments especially designed to prevent lipid oxidation is encouraged when commercializing this species in the frozen state.     

Studies on rancidity inhibition in frozen horse mackerel (Trachurus trachurus) by citric and ascorbic acids

This study is aimed to investigate the effect of aqueous solutions of citric acid (CA) and ascorbic acid (AA) on the lipid stability of horse mackerel (Trachurus trachurus) fillets and whole fish during frozen storage (up to 6 and 9 months, respectively) by means of a soaking pretreatment. Best oxidation inhibition results on fish fillets were obtained when employing a 0.5% CA solution. Lower (p <0.05) peroxide (month 3), thiobarbituric acid‐reactive substance (months 1 and 3) and fluorescent compound formation (month 6) values were obtained from CA‐treated fish fillets than from the untreated (blank control) and water‐treated (water control) fish fillets. In the case of whole fish, soaking pretreatment with a mixture consisting of 0.5% CA and 0.5% AA showed the best results in inhibiting oxidation, as lower (p <0.05) peroxide formation was observed at 6 and 9 months of frozen storage compared to the untreated or water‐soaked counterparts. Advantages of both acids (CA and AA) are discussed, and further studies based on the positive role of a CA‐AA mixture will be carried out to extend the shelf life of medium‐ and high‐fat content fish species during frozen storage.     

Damage detection in horse mackerel (Trachurus trachurus) during chilled storage

Sensory and chemical analyses were performed during the chilled storage of whole and filleted horse mackerel (Trachurus trachurus), an underutilized medium-fat fish species. For both kinds of fish products, satisfactory correlations with the storage time were obtained for amine formation (total volatile basenitrogen and trimethylamine-nitrogen), lipid damage (free fatty acid formation), and formation of interaction compounds (fluorescence detection in the aqueous phase). Sensory analyses showed a gradual lower grading with time, with a shelf life of 14 d for whole-fish samples and 12 d for fillet samples. Correlation and multivariate analyses between the sensory attributes and the chemical indices showed that trimethylamine-nitrogen detection was the most accurate chemical method for damage assessment during the chilled storage of whole and filleted horse mackerel.     

Rancidity development during the chilled storage of farmed Coho salmon (Oncorhynchus kisutch)

Coho salmon (Oncorhynchus kisutch) is a fatty fish species whose farming production has greatly increased in recent years. Lipid damage produced during Coho salmon chilled storage was studied for up to 24 d. Lipid hydrolysis (free fatty acids, FFA) and oxidation (conjugated dienes; peroxide value, PV; thiobarbituric acid index, TBA‐i; fluorescent compounds formation, FR; browning development) were determined and compared to lipid composition (polyene index, PI; astaxanthin, AX) changes and sensory assessment (rancid odour development) results. Most lipid damage indices developed slowly during storage; thus, values obtained for FFA, PV, TBA‐i and FR were in all cases under 1.5 g/100 g, 4.0 meq oxygen/kg lipid, 0.40 mg malondialdehyde/kg muscle and 0.40, respectively. Odour assessment showed a significant (p <0.05) rancidity development at day 10, when compared to starting fish material; then, non‐acceptable values were obtained at days 19 and 24. The PI analysis showed not many differences during the storage time, with the lowest mean value at day 19. AX analysis indicated a relatively high content in the white muscle, which was maintained till the end of the experiment. A low oxidation development is concluded for Coho salmon lipids when compared to other fatty fish species under the same chilling conditions. AX was found to contribute to the oxidation stability of Coho salmon lipids, due to its free radical scavenger properties.     

Effect of advanced chilling methods on lipid damage during sardine (Sardina pilchardus) storage

Slurry ice is a biphasic system consisting of small spherical ice crystals surrounded by seawater at subzero temperature. Its effect on lipid damage (hydrolysis and oxidation) was evaluated during the chilled storage of a fatty fish species, sardine (Sardina pilchardus). Slurry ice treatment was checked alone and in combination with ozone and compared to traditional flake icing during a 22‐day storage. Different lipid damage indices (free fatty acids, FFA; peroxide value, PV; thiobarbituric acid index, TBA‐i; fluorescent compounds, FR) were checked and compared to sensory assessment and nucleotide degradation (K value). According to lipid hydrolysis (FFA) and oxidation (PV and FR) developments, slurry ice showed an inhibitory effect (p <0.05) on lipid damage during storage, as well as an inhibition of nucleotide autolytic degradation. Ozonised slurry ice did not provide differences (p >0.05) from slurry ice alone when considering lipid hydrolysis, nucleotide degradation and some lipid oxidation indices (PV and FR), although a higher (p <0.05) TBA‐i was observed at day 22 of storage when compared to flake ice and slurry ice treatments. However, a lower (p <0.05) fluorescence development was observed for fish treated under ozonised slurry ice when compared to traditionally iced fish. Sensory assessment showed a higher shelf life for fish samples treated under ozonised slurry ice than for their counterparts under slurry ice (15 d versus 12 d), while flake icing led to a far shorter shelf life (5 d). According to sensory and biochemical (lipid matter and nucleotide) analysis, slurry ice has proved to be a promising technology for damage inhibition and quality retention in a fatty fish species such as sardine. Ozonised slurry ice was also shown to be useful, since a longer shelf life was obtained in the present experiment and a pro‐oxidant effect of ozone on sardine lipids was not proved.