Factors Influencing Liquid-holding Capacity and Structural Changes During Heating of Comminuted Cod (Gadus morhuaL.) Muscle

Abstract The loss of liquid in cod muscle finely comminuted with salt was studied as a function of heating temperature from 5 to 70 °C. Three different groups of raw material were tested: wild and farmed maturing cod and wild post-spawn cod. The effects of ionic strength, pH and heating temperature upon liquid-holding capacity were examined either individually or simultaneously by using a general linear statistical model. The liquid-holding capacity was measured by a low-speed centrifugation net test. The microscopic changes of the comminuted samples were evaluated by light microscopy. The intact muscle, used as raw material, was investigated with light and transmission electron microscopy. The liquid loss was very low and almost constant between 5 and 30 °C, and increased rapidly thereafter at elevated temperatures. NaCl concentration, pH, heating temperature and interactions among these factors influenced the liquid released according to a first-order interaction linear model. Upon comminution with salt, most of the fibre structure is lost and a homogeneous phase is formed from the depolymerized myofibrils. Pores and gaps appeared in the protein matrix upon heating, enhancing the liquid loss. Melted collagen was seen either as a thin film or as an aggregated network structure, depending on the temperature, in the aqueous phase filling the pores and gaps. Wild, maturing cod possessed better liquid-holding capacity at higher heating temperatures than did both farmed and post-spawn fish, owing to different fibre structure. Post-spawn fish had underwent a more severe degradation than did the maturing fish during ice-storage.