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 ac tivities of alpha -glucosidase and beta -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 i n 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 degreesC), a small non-significant increase in non-heme iron content was observed with a concomitant decrease in heme iro n. Thiobarbituric acid-release substance increased significantly (P < 0.05) , especially for the fillets subjected to five freeze-thaw cycles. Componen ts with spectral characteristics similar to hydrogen peroxide-activated hem oproteins were detected with a concomitant decrease in metmyoglobin content in five-cycle freeze-thawed samples after 3 days of storage. The freeze-th aw process therefore has a detrimental effect on the quality of catfish fil lets, particularly after chilled storage. (C) 2001 Elsevier Science Ltd. Al l rights reserved.