Ultrastructure of the Myofibrillar Component in Cod (Gadus morhua L.) and Hake (Merluccius merluccius L.) Stored at −20 °C as a Function of Time

Transmission electron microscopy and image analysis techniques were used to study the ultrastructure of the myofibrillar component in cod and hake muscle stored at -20 degrees C for varying periods of time. Cod muscle showed a deformation of the hexagonal array of thick filaments with the storage time, reflected in an increase in the eccentricity value, a parameter defined to measure changes in the ratio of maximum to minimum hexagon diameter, and an increase in the cross-linkings between the filaments. Degradation of cod thick filaments leading to detachment was also visible upon prolonged storage. In hake muscle significant changes were not found in the arrangement and morphology of thick filaments during frozen storage, suggesting a high incidence of intrafilament aggregation. The ultrastructural differences in the array of thick filaments between species were accompanied by a difference in the textural measurements.