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 pres sure release, i.e. Pressure Shift Freezing (PSF, 140 MPa, - 14 degreesC) or hv air-blast (ABF, - 20 degreesC), and were then stored at 20 degreesC for 75 days. Changes in protein stability, texture, TEA number. free fatty aci d 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 sample s as compared to non frozen samples. These modifications were correlated wi th a decrease in the apparent viscosity of the salt soluble protein extract of pressure shift frozen samples and with a significant decrease in the in tensity of the myosin heavy chain showed by electrophoresis. Air-blast free zing induced lower changes in protein extractability but the toughness of f illets frozen by this process increased with storage time and was significa ntly higher than that of pressure shift frozen samples after 75 days of sto rage. No particular influence of these two processes of freezing was notice d for the free fatty acid contents. Pressure shift frozen turbot fillets ap peared more opaque after 2 days of storage but this change was not accentua ted during frozen storage. (C) 2000 Academic Press.