Viscoelastic properties of lactoferrin/ β-lactoglobulin coacervates studied by rheology and micro rheology

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anglais. Heteroprotein complex coacervates (HPCC) has great potential in many food applications. However, understanding the rheology-coacervate structure relationship, as well as their sensitivity to slight changes in the physicochemical environment, is still an active research topic. Herein, HPCC between two oppositely charged proteins, lactoferrin (LF) and β-lactoglobulin (βLG) was investigated. The influence of ionic strength and temperature on the rheological properties of LF/βLG coacervates was examined using oscillatory shear rheology and microrheology from dynamic light scattering. LF/ßLG HPCC exhibited a liquid-like character with G'(ω) < G''(ω) and an increase of both moduli with decreased temperature but a softening effect with increased ionic strength. The dependency of G' and G'' on angular frequency (ω) demonstrated a scaling of G"∼ω 1 and a lack of terminal behavior with G'∼ω 1.4. The application of time-temperature superposition (TTS) and time-salt superposition (TSS) principles allowed the prediction of the rheological properties over a wide range of timescales and temperatures below the denaturation temperature of βLG and LF. The two principles suggested that increasing temperature or ionic strength accelerates coacervates dynamics but does not affect largerscale physics. Microrheology experiments using polystyrene-coated microspheres as tracers, allowed access to a frequency range up to (ω ∼ 106 rad/s) and revealed a variable scaling of G'= G" ∼ ω 1/2 or ω3/4 at the high-frequency terminal regime and approaching theoretical predictions of Rouse regime and Worm-Like Chain model for polymers. In the present case, it reflected a freely draining system where hydrodynamic interactions are neglected at these timescales. This study offers new insights into the microstructure of HPCC, relevant to various applications, as function of ionic strength and temperature.