Viscoelastic and flow behaviour of β-lactoglobulin/lactoferrin coacervates: Influence of temperature and ionic strength.

Heteroprotein complex coacervation has potential for a wide range of applications. However, the sensitivity of coacervates to slight changes in physico-chemical conditions may constitute a technological barrier for their development and deserves to be better understood. In this study, the rheological properties of β-lactoglobulin/lactoferrin (βLG/LF) heteroprotein complex coacervates were investigated with respect to narrow changes of temperature (5-40 °C) and ionic strength (0 to 10 mM added NaCl). The apparent viscosity of βLG/LF coacervates prepared at 20 °C showed a high sensitivity to temperature, decreasing progressively at elevated temperatures. Frequency sweep experiments demonstrated that coacervates behave as a viscoelastic liquid throughout the investigated frequency range at T>10°C. Time-temperature superposition principle revealed that the interaction involved in the coacervation process were temperature-independent. The calculated activation energy was approximately 85 kJ/mol. The addition of NaCl (up to 10mM) prior to coacervation, resulted in an increase of the viscosity but did not show a clear trend in the evolution of viscoelastic moduli. These new insights allow a better understanding of the interactions involved in concentrated protein coacervates enabling better control over their potential uses.