Characterisation and thermo-reversible gelation of cod muscle protein isolates

Cod (Gadus Morhua) muscle proteins were solubilized using alkaline treatment of the muscle. Solutions of similar protein composition were obtained between pH 10.5 and 12.0, however, pH > 11 was required for optimal yield. Addition of salt (up to 0.25 M NaCl) did not affect protein yield or composition. Light scattering showed that a significant fraction of the proteins was present as large self similar and flexible aggregates. When the pH was decreased below 10, gelation was observed below a critical temperature of about 25 °C, which could be reversed by heating. Slow irreversible aggregation was also observed leading to coarsening and syneresis of the gels or precipitation at higher temperatures. The rate of irreversible aggregation increased with decreasing pH and was fast below pH 8. Homogeneous thermo-reversible self supporting gels that were stable for a period of days could be prepared without heating at a narrow pH range between 8.5 and 9.5.