Rheological characterization of β-lactoglobulin/lactoferrin complex coacervates

Heteroprotein complex coacervation between lactoferrin (LF) and β-lactoglobulin (β-LG), two oppositely charged proteins from whey, occurred under specific conditions of pH, ionic strength and protein molar ratio. The present work aims at characterizing the rheological properties of the concentrated phase called coacervate obtained after phase separation. Unlike some polysaccharide/protein coacervates, β-LG/LF heteroprotein coacervates exhibit a liquid-like behavior; the loss modulus G” being 100 times higher than the storage modulus G’ at low frequencies. This behavior was confirmed under creep-recovery tests. The heteroprotein coacervates exhibited a Newtonian viscous flow under low shear rate and a shear thinning behavior above 10 s−1. The coacervates are exceptionally viscous, reaching a viscosity value of 55 ± 10 Pa.s which is ∼2500 times higher than that measured on individual protein solutions of equivalent total concentration. Also, a structural change occurred in the coacervates, probably due to the weaknesses of electrostatic interactions inside the protein network at high shear rates. The observed time-dependent structural rearrangement was proved to be reversible. These findings open new ways for the use of coacervates as texturizing agents in food matrices.