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.