Seasonal variation of antifreeze glycoprotein and sensitivity to biochemical damage by partial freezing in muscle from Atlantic cod, GADUS MORHUA, L

Simpson, Marian Victoria (1986) Seasonal variation of antifreeze glycoprotein and sensitivity to biochemical damage by partial freezing in muscle from Atlantic cod, GADUS MORHUA, L. Masters thesis, Memorial University of Newfoundland.

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Abstract

Live Atlantic cod Gadus morhua were acclimated at 0°C or 10°C for at least three weeks and studied as well as cod fish held at ambient water temperature to determine, the effect of habitat temperature on the keeping qualities of fish during low temperature storage. Cod fillets were stored in ice (0 ± 0.2°C) or partially frozen (-3 ± 0.1°C) for various time intervals to evaluate the effectiveness of the two methods in preserving fish freshness. The criteria employed for the evaluation of biochemical deterioration were changes in (i) extractable protein, (ii) free amino acids, (iii) "extracellular area", (iv) levels of TMAO-N, TMA-N, and DMA-N, (v) free drip and (vi) cell fragility. -- Freezing point and melting point measurements of the muscle fluids or blood plasma derived from cod fish acclimated to cold temperature (0°C) or from cod fish caught in the winter months demonstrated thermal hysteresis, unlike similar samples derived from cod fish acclimated to warm temperature (10°C) or cod fish maintained at ambient water temperature caught in the summer months. This finding implies that antifreeze proteins are present in the muscle fluid of cod fish when the habitat temperature is low, but absent when the habitat temperature is high. -- Partial freezing proved to be a more effective method of minimizing biochemical damage than ice storage as judged by the capacity of the partially frozen samples (i) to retain relatively higher levels of extractable protein, (ii) to exhibit less depletion of free amino acids, (iii) to form relatively lower levels of TMA and DMA, (iv) less increase in extracellular area, and (v) to maintain better consumer acceptability during sensory evaluation studies.

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