Abstract:
Effects of moisture content, pH, and salt concentration on dynamic rheological properties and gel fracture quality of Pacific whiting surimi were investigated. Torsion tests showed that shear stress decreased rapidly and strain values decreased gradually as moisture concentration increased. As pH increased, fracture shear stress and strain values increased, whereas lightness values (L*) decreased. Increasing salt concentration up to 1% increased fracture shear stress
and strain values, but further increase affected negatively. A strong relationship was found between the G' and fracture stress values as affected by moisture or pH, but not by salt concentration. Linear regression analyses indicated that while moisture concentration and pH can be used as an index estimating final gel quality, salt concentration cannot be used. Thermal stability, proteolytic enzyme degradation, and thermal aggregation patterns of myofibrillar proteins from various fish species were also compared. There was a species effect for both optimum setting and chopping temperatures. While cold water fish species had the highest shear stress values at 5 °C or lower temperatures, warm water fish species had higher fracture shear stress values at 20-30 °C. Proteolytic enzyme activity increased linearly with incubation time when the test was conducted at the optimum autolysis temperature up to 240 mm. SDSPAGE analysis showed that myosin heavy chain was the major protein targeted by proteolytic enzymes. For all tested fish species, a 0.5 °C/min heating rate resulted in higher turbidity values followed by 1 °C/min, and then 2 °C/min. There was a species effect on the temperature where turbidity started to increase. The transition temperatures obtained from temperature sweep measurements were very close to those obtained from DSC, indicating that peaks obtained from the dynamic tests were related to the protein unfolding.
