Rheology and microstructure of heat-induced fluid gels from Antarctic krill (Euphausia superba) protein: Effect of pH

Antarctic krill (Euphausia superba) offers a high potential for development of innovative food products due to its large reserves and satisfied nutritional values. This study aimed to evaluate the thickening function of heat-induced krill protein fluid gels through the investigation of their flow behavior and microstructure. The microstructure of these physical gels was classified as four types, including particulate gels (pH 5.5), transition state from particulate to branched gels (pH 6.0), loose connected networks (pH 6.8, 7.0, 8.0 and 8.6) and fine cross-linked structure (pH 6.4, 7.2 and 7.5). Gels at pH 5.5 and 7.2 showed significantly higher gel strength in comparison with their counterparts at other pHs. Fluid gels showed characteristic non-Newtonian pseudoplastic behavior with low flow behavior indexes in the shear thinning region. Fluid gels at pH 7.2 showed significantly higher viscosity in comparison with other gels, which was related with its viscoelasticity and microstructure. Fluid gels with branched networks exhibited significantly better water binding capacities than particulate gels. Fluid gels became less pseudoplastic as temperature increased, which resulted from the melting of gels. The thixotropy of fluid gels was demonstrated through loop test, stepwise test and start-up flow experiment. Particulate gels at pH 5.5 showed smaller thixotropy in comparison with branched gels at higher pHs. Fine connected fluid gels showed lower structural recovery than loose cross-linked gels under stepwise test. This resulted from the irreversible damage of fine connected structure under high shear rate. Heat-induced fluid gels of krill protein exhibited thickening function and could be applied in food development with desired requirement.