On the (Micro)Rheology of Lactoferrin/β-Lactoglobulin Coacervates

International audience

English. 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 oppositelycharged proteins, lactoferrin (LF) and β-lactoglobulin (βLG) was investigated. The influence of ionic strengthand temperature on the rheological properties of LF/βLG coacervates was examined using oscillatory shear rheology and microrheology from dynamic light scattering. LF/βLG 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” ∝ ω1 and a lack of terminal behavior with G’ ∝ ω1.4. The application of time-temperature superposition (TTS) nd 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 larger-scale 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” ∝ ω1/2 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. By combining rheology and microrheology, we provide a comprehensive study that underscores the influence of ionic strength and temperature on LF/βLG coacervates.This study highlights the similarities and differences between protein coacervates and polymer systems and offers new insights into the microstructure of HPCC relevant to various applications.