Microstructure and flow behaviour of liquid water-gelatin-locust bean gum systems

Liquid water-gelatin-locust bean gum (LBG) systems, in the conditions of lowest compatibility (near the isoelectric pH of the protein), were explored using confocal laser scanning microscopy and viscometry. Confocal microscopy observation proved to be a more sensitive method to assess the phase state of the systems than the: usual centrifugation or viscometric ones. It showed that in fact the system is already phase-separated well below the apparent binodal line determined by the other methods. When the continuous phase is enriched in LEG. the observed microstructure is of the expected type with spherical droplets of gelatin dispersed in the LBG phase. Bicontinuous systems were observed close to the inversion point, which is clearly detected by viscosity measurements; beyond this point, the gelatin enriched continuous phase contained large inclusions of LBG, apparently due to aggregation of the LEG disperse phase. For systems with a LEG enriched continuous phase, shear thinning behaviour, similar to that of a LEG solution, was observed; the low newtonian viscosity decreased as the volume fraction of the gelatin disperse phase increased, following approximately the usual logarithmic additivity law. In the reverse case, where the continuous phase is enriched in gelatin, flow curves with an apparent yield stress and a negative deviation from the logarithmic additivity law were observed. The variation of the viscosity with the volume fraction of the disperse phase obeyed approximately the equation of Palierne for systems of two viscoelastic phases when the interface is purely elastic. The microstructure of phase-separated mixtures depends on the phase viscosity ratio, which also determines the differences in flow behaviour. (C) 2001 Elsevier Science Ltd. All rights reserved.