Effect of sodium chloride on formation and structure of whey protein isolate/hyaluronic acid complex and its ability to loading curcumin

Effects of ionic strength (0-150 mM NaCl) on formation and properties of whey protein isolate (WPI) and hyaluronic acid (HA) complexes (WPI/HA = 4:1, total concentration of 0.1%, w/w) were investigated. Subsequently, coacervates with corresponding NaCl were applied as delivery vehicle for curcumin. Turbidity analysis showed that NaCl enhanced WPI and HA complexation at 5-40 mM. Adding NaCl (0-150 mM) shifted pH(phi 1) and pH phi 2 towards lower and higher pH values, respectively. Zeta potential measurement showed that surface charge of complexes decreased with increasing NaCl concentration. Circular dichroism and fluorescence spectra indicated that alpha-helix content and fluorescence intensity of WPI involved in complexation changed with increase of varied NaCl concentration. Isothermal Titration Calorimetry data and Confocal Laser Microscope analysis showed that screening effect of NaCl hindered electrostatic interaction, whereas hydrophobic force may promote complexation at NaCl concentration of 0-30 mM. Fluorescence quenching data revealed that presence of salt at low (5-40 mM) and high (50-150 mM) levels increased and decreased binding ability of WPI/HA with curcumin, respectively. Presence of salt at 5-40 mM improved particle size, encapsulation efficiency and loading capacity compared with control. Data demonstrated that critical NaCl concentration was around 40 mM and this finding could facilitate applications of WPI/HA complex as delivery vehicle of bioactive substances.

Automated summary

The study investigated the effects of ionic strength on the formation and properties of WPI and HA complexes, showing that NaCl concentration of 5-40 mM had the most significant enhancement on the complexation. The presence of NaCl affected pH values, surface charge, conformation, and fluorescence intensity of the complexes. The critical NaCl concentration for optimal complexation was around 40 mM, indicating potential applications of WPI/HA complexes as delivery vehicles for bioactive substances.