Physicochemical and enzymatic changes of cod muscle proteins subjected to different freeze-thaw cycles

Abstract

The effects of freeze–thaw cycles on the physicochemical and enzymatic changes of cod muscle proteins were investigated. The activities of α-glucosidase and β-N-acetyl-glucosaminidase increased as the the number of freeze–thaw cycles increased. A loss of Ca2+-ATPase and Mg2+-Ca2+-ATPase activities was observed, while Mg2+-EGTA-ATPase activity increased, especially after one cycle of freezing–thawing, with a concomitant decrease in Ca2+ sensitivity. The surface sulphhydryl group content decreased with increasing freeze–thaw cycles, while no changes in total sulphhydryl group content were found. The surface hydrophobicity of actomyosin did not change significantly with the number of freeze–thaw cycles. The loss of protein solubility increased with increasing freeze–thaw cycles. However, no cross-linked proteins induced by formaldehyde were found. The results revealed that freeze–thaw cycles directly affected the physicochemical and enzymatic properties of cod muscle proteins. © 2000 Society of Chemical Industry