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


Soottawat Benjakul, Asst. Prof., D. of Food Tech., F. of Agro-Industry, PSU.
Friedrich Bauer, Inst. of Meat Hygiene, Meat Tech. and Food Sci., U. of Veterinary Medicine, Vienna, Australia

Grant : Austrian Academic Exchange Service (AD)
Published : J Sci Food Agric 2000, 80 : 1143-1150
Key words : freezing-thawing, frozen storage, cod, muscle protein, physicochemical properties

The effects of freeze-thaw cycles on the physicochemical and enzymatic changes of cod mus-cle proteins were investigated. The activities of a-glucosidase and b-N-acetyl-glucosaminidase in-creased as 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 sulfhydryl group content decreased with increasing freeze-thaw cycles, while no changes in total sulfhydryl 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.

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