Influence of glycerol on optical properties and large-strain rheology of heat-induced whey protein isolate gels

The influence of glycerol (0–50 wt%) on the properties of gels formed by heating 10 wt% whey protein isolate (WPI) solutions (pH 7.0, 100 mM NaCl) at 90 °C has been studied. The elastic modulus, breaking stress and breaking strain of the gels were measured using uniaxial compression. The optical properties of protein solutions were characterized by turbidity or colorimetry measurements. The onset of gelation at 90 °C was delayed in the presence of glycerol, presumably because the cosolvent increased the thermal stability of the globular proteins and reduced the protein–protein collision frequency. On the other hand, the elastic modulus, breaking stress and breaking strain of gels heated at 90 °C for 60 min increased with glycerol concentration, presumably because the glycerol increased the strength of the intermolecular attraction between fully denatured proteins. Glycerol decreased the lightness of the gels because it reduced the scattering efficiency of the protein aggregates. This study shows that glycerol can be used to modulate the physicochemical properties of whey protein gels.