Rancidity development during the frozen storage of farmed coho salmon (Oncorhynchus kisutch): effect of antioxidant composition supplied in the diet

Abstract

A commercial diet including synthetic antioxidants (BHT-ethoxyquin mixture) (diet I) was provided to coho salmon (Oncorhynchus kisutch) in parallel with two diets including natural antioxidants (tocopherol isomers rich Mixture, diet II; tocopherol isomers-rosemary extract mixture, diet III). A comparative study of the rancidity development in the corresponding frozen (-18 degrees C products was undertaken. When compared to fish fed with diet I, individuals corresponding to diet II showed a greater (p < 0.05) retention of primary (conjugated dienes and peroxides content) and secondary (anisidine and thiobarbituric acid indices) lipid oxidation compounds that led to a lower interaction compound formation (fluorescence ratio ranges: 0.33-0.50 and 0.55-0.85, for diet II and diet I individuals, respectively); likewise, a higher polyene index (1.99-2.14 and 1.72-1.97, respectively) and lower oxidised taste scores (0.0-0.6 and 0.0-2.4, respectively) were obtained. No effect (p > 0.05) on lipid hydrolysis development (free fatty acid formation) could be found as a result of employing different diets.