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

Liquid water-gelatin-locust bean gum (LBG) systems, in the conditions of lo west compatibility (near the isoelectric pH of the protein), were explored using confocal laser scanning microscopy and viscometry. Confocal microscop y observation proved to be a more sensitive method to assess the phase stat e of the systems than the: usual centrifugation or viscometric ones. It sho wed that in fact the system is already phase-separated well below the appar ent binodal line determined by the other methods. When the continuous phase is enriched in LEG. the observed microstructure is of the expected type wi th spherical droplets of gelatin dispersed in the LBG phase. Bicontinuous s ystems were observed close to the inversion point, which is clearly detecte d by viscosity measurements; beyond this point, the gelatin enriched contin uous phase contained large inclusions of LBG, apparently due to aggregation of the LEG disperse phase. For systems with a LEG enriched continuous phas e, shear thinning behaviour, similar to that of a LEG solution, was observe d; the low newtonian viscosity decreased as the volume fraction of the gela tin disperse phase increased, following approximately the usual logarithmic additivity law. In the reverse case, where the continuous phase is enriche d in gelatin, flow curves with an apparent yield stress and a negative devi ation from the logarithmic additivity law were observed. The variation of t he viscosity with the volume fraction of the disperse phase obeyed approxim ately the equation of Palierne for systems of two viscoelastic phases when the interface is purely elastic. The microstructure of phase-separated mixt ures depends on the phase viscosity ratio, which also determines the differ ences in flow behaviour. (C) 2001 Elsevier Science Ltd. All rights reserved .