Effect of Freezing and Frozen Storage on Salt Penetration Into Fish Muscle Immersed in Brine

Salting is a processing treatment used either to provide a salty flavor or to impart storage stability by decreasing water activity. Optimum salt content can enhance overall flavor acceptability and is a major factor in safe preservation of smoked fish. In this study, rate of salt penetration into fresh or frozen and then thawed fish muscle was studied by dipping mullet fillets in brine. Salt penetration curves resemble a first order change [X = C(l ‐ e −kt )]. Initial salt penetration rate (g salt/g sample/ min) and rate constant (min −1 ) increased respectively from 0.006 and 0.018 for fresh fish to 0.014 and 0.029 after freezing (frozen for 1 wk), then decreased to 0.011 and 0.025 after 3 wk of frozen storage, and leveled off at 0.009 and 0.018 from 5–9 wk of storage. The change in salt penetration rates closely followed changes in extractable actomyosin in muscle, indicating a dependence of the change on the degree of denaturation of fish muscle proteins. The effects of brine concentration and frozen storage on water transfer were also studied. Water migrated from the brine into the flesh if fresh mullet fillets were dipped in brine at concentrations up to 15%. When the brine concentration was 20% or higher, the water migated from fish muscle to the brine. However, after 2 months frozen storage, fish muscle gained water if dipped in brine of 20% or below and lost water when the brine was 25% or higher.