Biochemical and physicochemical changes in catfish (Silurus glanis Linne) muscle as influenced by different freeze–thaw cycles

Freeze–thaw cycles affected the biochemical and physicochemical properties of catfish fillets. When the number of freeze–thaw cycles increased, the activities of α-glucosidase and β-N-acetyl-glucosaminidase increased (P<0.05). No increase in non-heme iron content was observed (P>0.05); however the heme iron content decreased (P<0.05). This suggested that the freeze–thaw process caused damage of the cell and hemeprotein, resulting in the release of pro-oxidants. No differences in metmyoglobin and autolysis products (P>0.05) were found as affected by freeze–thaw cycles. After 3 days of chilled storage (2–4°C), a small non-significant increase in non-heme iron content was observed with a concomitant decrease in heme iron. Thiobarbituric acid-release substance increased significantly (P<0.05), especially for the fillets subjected to five freeze–thaw cycles. Components with spectral characteristics similar to hydrogen peroxide-activated hemoproteins were detected with a concomitant decrease in metmyoglobin content in five-cycle freeze–thawed samples after 3 days of storage. The freeze–thaw process therefore has a detrimental effect on the quality of catfish fillets, particularly after chilled storage.