Rheology of thermo-reversible fish protein isolate gels

Fish protein isolates (FPI) from cod muscle were studied at pH 9 and 11. Thermo-reversible gels, stable at and below room temperature could be produced at both pH values. Application of low shear stress to the gels led to an initial elastic response followed by a power-law deformation (creep) at both pH. Above a critical shear stress gels fractured and flowed regularly with a viscosity of about 0.05 Pa s.Strain–stress curves were recorded using both flow and oscillatory measurements. For all systems strain-hardening was observed followed by fracture. Fracture occurred at approximately the same deformation, but the amplitude of strain-hardening and the yield stress decreased with decreasing rate of the stress ramp. Results obtained from oscillatory shear at 1 or 0.1 Hz were close to those obtained with continuous shear during the fastest stress ramps.The structure of the gels was investigated using confocal laser scanning microscopy and turbidity measurements.