Rheology of whey protein isolate‐xanthan mixed solutions and gels. Effect of pH and xanthan concentration

Abstract

AbstractFlow properties at pH 5.5‐7.5 of whey protein isolate (WPI)‐xanthan solutions containing 0‐0.5 w/w% xanthan were studied by viscosimetry, although rigidity and fracture properties of the corresponding heat‐set gels (90°C, 30 min) were determined by uniaxial compression. All the studied solutions displayed generalized shearthinning flow behaviour. Synergistic WPI‐xanthan interactions has been revealed by observing that rheological parameters [σmsf, K, n, η (γ)] characterizing blends were larger than those calculated from the two separated solutions. Such a behaviour was attributed to segregative phase separation of whey proteins and xanthan.Effects of xanthan on WPI‐xanthan gel properties both depended on pH and xanthan concentration. Simultaneous increased xanthan concentration and decreased pH inhibited gelation of WPI‐xanthan blends. Regarding gel strength, synergistic WPI‐xanthan interactions were observed at pH >7.0 and low xanthan concentration (0.05 or 0.1 w/w%). Antagonism between the two macromolecules occurred at low xanthan concentration and pH ≤6.5, and high xanthan concentration (0.2 or 0.5 w/w%) at all pH tested. Low xanthan concentration rendered mixed gels more brittle than protein gels, and high xanthan concentration decreased pH effects on gel stress‐strain relationships. The balance between strong thermal aggregation of concentrated whey proteins ‐ in presence of incompatible xanthan ‐, high viscosity of blends and repulsive surface forces of protein molecules was thought to be at the origin of WPI‐xanthan gel mechanical properties.