A comparison of biochemical changes in cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) fillets during frozen storage

Changes in the muscle proteins of frozen cod fillets, which produce significant amounts of formaldehyde, and frozen haddock fillets, which produce negligible formaldehyde, were compared. Protein extractability and hydrophobicity and the amino acid contents of soluble and insoluble proteins, as well as formaldehyde formation, were investigated in matching pairs of cod and haddock fillets stored at -10 and -30degreesC (control). Formaldehyde production in cod was much higher (845 and 1065 nmol g(-1) at 20 and 30 weeks respectively) than in haddock (93 and 101 nmol g(-1) after 20 and 30 weeks respectively) at -10degreesC. However, a rapid decrease in solubility of proteins, increase in hydrophobicity and decrease in the amino acid content of salt-soluble proteins at -10 compared with -30degreesC were observed in both species. The results showed that there were no significant differences in the nature of the protein changes between these two species, thus indicating that factors other than formaldehyde were involved in the denaturation of proteins and the formation of aggregates during frozen storage of cod and haddock fillets, especially at -10degreesC. (C) 2001 Society of Chemical Industry.