Charge density of polysaccharide controls microstructure and large deformation properties of mixed gels

Micro-phase separated mixed gels of whey proteins and polysaccharides were prepared by acid-induced cold gelation. Polysaccharides with different charge densities ranging from neutral (galactomannans) to one negative charge per monosaccharide (ι-carrageenan) were selected to alter the phase separated microstructure. The charge density turned out to be the dominant factor that determined the micro-phase separation. Next to the charge density, the weight average molecular weight and the chain stiffness played a role in this process. Approximately, the effect of charge density can be divided into three categories: below 0.3, between 0.3–0.7 and above 0.7 (defined as mol negative charge per mol monosaccharide). Each category showed its specific polysaccharide concentration dependency of the microstructure as determined by confocal laser scanning microscopy. The microstructure in turn determines the large deformation properties of the mixed gels. The large deformation properties of these micro-phase separated mixed gels were measured by uniaxial compression tests. Theory on the deformation behaviour of gels was used to relate the large deformation properties of these mixed gels to their microstructures.