Effect of the Helix-Coil Transition in Bovine Skin Gelatin on Its Associative Phase Separation with Lysozyme

Rheology and tribology of chitosan/Acacia gum complex coacervates

Acacia gum (Gum Arabic; GA) and chitosan (CTS) form complex coacervates in acidic environments, providing a polymer-rich aqueous material with interesting bio-lubricant properties. We investigate the interplay of the tribology and rheology of these coacervates, demonstrating that they dramatically reduce the friction coefficient between lubricated soft model surfaces as compared to solutions of the individual polymers. We characterize the phase separation behavior using microscopy, electrophoretic mobility and thermogravimetric analysis. The macroscopic rheological behaviour is predominantly viscous and ranges from weakly to strongly shear thinning: viscosity levels and strength of shear thinning increase with decreasing ionic strength, but no apparent yield stress or predominant elasticity were observed even in the absence of salt. Conversely, friction coefficients measured between soft and rough surfaces increase with a rise in ionic strength and can be scaled onto a Stribeck-type master curve across varying ionic strength and pH in the mixed and hydrodynamic lubrication regimes.

Heteroprotein complex coacervation: Focus on experimental strategies to investigate structure formation as a function of intrinsic and external physicochemical parameters for food applications

Proteins are important components of foods, because they are one of the essential food groups, they have many functional properties that are very useful for modifying the physicochemical and textural properties of processed foods and possess many biological activities that are beneficial to human health. The process of heteroprotein complex coacervation (HPCC) combines two or more proteins through long-range coulombic interaction and specific short-range forces, creating a liquid-liquid colloid, with highly concentrated protein in the droplet phase and much more diluted-protein in the bulk phase. Coacervates possess novel, modifiable, physicochemical characteristics, and often exhibit the combined biological activities of the protein components, which makes them applicable to formulated foods and encapsulation carriers. This review discusses research progress in the field of HPCC in three parts: (1) the basic and innovative experimental methods and simulation tools for understanding the physicochemical behavior of these heteroprotein supramolecular architectures; (2) the influence of environmental factors (pH, mixing ratio, salts, temperature, and formation time) and intrinsic factors (protein modifications, metal-binding, charge anisotropy, and polypeptide designs) on HPCC; (3) the potential applications of HPCC materials, such as encapsulation of nutraceuticals, nanogels, emulsion stabilization, and protein separation. The wide diversity of possible combinations of proteins with different properties, endows HPCC materials with great potential for development into highly-innovation functional food ingredients.