The microstructure and rheology of homogeneous and phase separated gelatine gels

Abstract

The gelation of gelatine in mixtures of gelatine (type A or type B) and globular proteins (Whey Protein Isolate (WPI), Whey Protein Aggregates (WPA) and Soy Protein Isolate (SPI)) was studied with a focus on their phase separation during gelation. Confocal laser scanning microscopy, visual observations and rheology were used to link the changes on a microscopic scale to macroscopic gel properties (visual appearance and gel stiffness).An increase in storage modulus G′ compared to single gelatine gels was observed for protein mixtures containing gelatine and SPI or gelatine and WPA. This could be related to segregative phase separation between proteins during gelatine gelation as detected by CLSM and visual observations. In protein mixtures without phase separation (Gelatine/WPI mixtures) the storage modulus G′ of the gels was the same as in pure gelatine gels. Since all protein mixtures were prepared at an ionic strength of 150 mM, where the electrostatic interactions were screened, the occurrence of phase separation was attributed to the excluded volume interaction between gelatines and globular proteins.