Protein denaturation in frozen fish. VII.—Effect of the onset and resolution of rigor mortis on denaturation

Pre‐rigor frozen cod were found to be less denatured than post‐rigor material under a wide range of conditions, ‚denaturation’︁ being loss of salt‐solubility of the proteins. Pre‐rigor frozen cod only became less soluble in salt solution than post‐rigor fish when the muscle was able to contract freely on thawing out. This occurred when bits, of the order of 1 g., or thin strips were thawed quickly. If the fragments were thawed slowly, or if whole fillets or entire fish were used, the contraction did not take place and the protein was not affected. The salt‐solubility of fresh pre‐rigor muscle (‚never‐frozen’︁) was always low compared with that of post‐rigor muscle, and it was found that if pre‐rigor muscle went into rigor as fillets, not as whole fish, i.e., was free to contract, the salt‐solubility remained low indefinitely.