Effect of Pressure Shift Freezing, Air-blast Freezing and Storage on Some Biochemical and Physical Properties of Turbot (Scophthalmus maximus)

One-hundred g samples of packaged turbot fillets were frozen either by pressure release, i.e. Pressure Shift Freezing (PSF, 140 MPa, -14°C) or by air-blast (ABF, -20°C), and were then stored at -20°C for 75 days. Changes in protein stability, texture, TBA number, free fatty acid content and colour were investigated. Important changes in extractability of salt soluble proteins were observed 2 days after freezing for pressure shift frozen samples associated by an increase in toughness of these samples as compared to non frozen samples. These modifications were correlated with a decrease in the apparent viscosity of the salt soluble protein extract of pressure shift frozen samples and with a significant decrease in the intensity of the myosin heavy chain showed by electrophoresis. Air-blast freezing induced lower changes in protein extractability but the toughness of fillets frozen by this process increased with storage time and was significantly higher than that of pressure shift frozen samples after 75 days of storage. No particular influence of these two processes of freezing was noticed for the free fatty acid contents. Pressure shift frozen turbot fillets appeared more opaque after 2 days of storage but this change was not Aaccentuated during frozen storage.