Heat-induced flocculation of microparticulated whey proteins (MWP); consequences for mixed gels made of MWP and β-lactoglobulin

Abstract

Flocculation/aggregation processes occurred when suspensions of microparticulated whey proteins (MWP) were heated (or sheared). Large flocs were observed above both a critical volume fraction ( Φ MWP>0.099) and a critical temperature ( T>60 °C). These large structures combined at high volume fraction to form a coarse network which developed a liquid-like viscoelastic response. The rheological and structural consequences of such instabilities on mixed heat-set gels made of MWP and β-lactoglobulin (BLG) were studied. In particular, cooperative effects at low MWP volume fraction were observed. In addition, steric hindrance effects or thermodynamic incompatibility could occur between the two components at high MWP volume fraction leading to micro-phase separation in the mixed system. The theory of van der Poel failed to describe the experimental results. This was attributed to the strongly flocculated state of the MWP system and to the chemical affinity of MWP for the BLG network. These views were supported by diffusing wave spectroscopy measurements and confocal scanning laser microscopy observations.