English abstract
King fish (Scomberomorus Commerson) is one of the important types of fish TUL consumed in Oman and other Gulf countries. In this research thermal transition and water sorption properties of king fish are studied in order to understand its storage stability. Freeze dried fish samples with the water content about 6.2% (wet basis) were used to study thermal transitions of whole fish muscle, fat, and fat-free muscle by Differential Scanning Calorimetry (DSC). The fat was separated from protein muscle by using Soxhlet method.
The initial freezing points of whole fish muscles were measured at different water contents
lrye using a cooling curve method and modeled as a function of water content by using the Chen equation. The cooling curve method gives initial freezing point temperatures which
were similar to the results obtained using DSC method at high water content and then the
two results deviated as solid contents of the sample increased. Water adsorption isotherm of whole fish muscle and fat free muscle were measured at room temperature (-23°C) using the isopiestic method and the data were modeled with BET and GAB equations. (The BET
monolayer water values were found to be 3.6% and 4.8% (dry basis) for whole and fat free
MU muscles, whereas the GAB monolayer values were found to be 5.2% and 8.6%, respectively.) The difference in monolayer water values - between the whole fish muscle
and fat free muscle - may be due to the difference in the amount of fat. The whole fish
muscles with unfreezable water showed thermal transitions in the range of -23°C to -2°C
with two endothermic peaks on DSC thermogram. The DSC thermogram of whole muscle
with freezable water did not show any glass transition but showed only one endothermic
peak of melting ice. The fat-free muscle showed thermal transitions at low and high temperatures, however it was difficult to justify that these are glass transition regions.
ogram) of the fat showed two endothermic peaks which illustrated the fat melting points of two fractions.
