Effect of freezing fish skins on molecular and rheological properties of extracted gelatin

Flounder skins were frozen at −12 or −20 °C, and the resulting gelatin preparations were compared with a gelatin extracted from fresh skins. Viscoelastic properties of gelatin preparations were studied using cooling and heating ramps straight after preparation and after 16–18 h of maturation at low temperature (7–8 °C). Maturation time influences greatly the viscoelastic properties and melting and gelling points of the resulting gels increasing the melting points, especially in the frozen skin gelatins. Gelatin from frozen skins at −12 °C had lower gel strength values when compared to the fresh skins but showed the highest melting point value. SDS–PAGE revealed that gelatin from fresh skins showed some high molecular weight aggregates and clear bands corresponding to α, β and γ-components. Gelatin from frozen skins showed less α and β-chains but more bands corresponding to lower molecular weight fragments; γ-components are less evident in both cases but especially in the case of skins frozen at −12 °C.