Effect of Temperatures on Fish Alkaline Protease, Protein Interaction and Texture Quality

ABSTRACT The effect of the activity of fish alkaline protease and protein denaturation on texture changes in mullet muscle during heating were studied. The proteolytic enzyme and the urea denatured hemoglobin substrate were incubated at different pH values and various temperatures. The enzyme activity was optimal at pH 8 and at 65°C. The extent of protein‐protein interactions in mullet actomyosin solutions increased with increasing temperature. The rate of protein‐protein interactions increased sharply as temperature increased from 35°C to 45°C at pH 6. When mullet muscle was heated at various temperatures ranging from 55°‐85°C, the shear force value increased (toughening) during the initial stage of heating and then decreased (softening). The toughening of fish flesh is probably due to muscle protein interactions, and the later tenderizing of fish flesh may be explained by alkaline protease activity (hydrolysis) masking the protein denaturation effect. When fish flesh was cooked at 100°C, no tenderizing effect was observed. This was probably due to loss of enzyme activity and only protein denaturation had significant effect on texture quality.