Viscosity z Shear thinning – Progressive orientation of molecules in direction of flow – Deformation of protein hydration sphere – Rupture of H- and other weak bonds z Dissociation of protein aggregates or networks z Apparent diameter of particles in direction of flow is reduced z The viscosity coefficient increases exponentially with protein concentration z Important for optimization of operations – Pumping, mixing, heating, cooling, spray drying
Viscosity z Shear thinning – Progressive orientation of molecules in direction of flow – Deformation of protein hydration sphere – Rupture of H- and other weak bonds z Dissociation of protein aggregates or networks z Apparent diameter of particles in direction of flow is reduced z The viscosity coefficient increases exponentially with protein concentration z Important for optimization of operations – Pumping, mixing, heating, cooling, spray drying
Gelation z A gel is a continuous network of macroscopic dimensions immersed in a liquid medium exhibiting no steady-state flow z Denatured proteins z Thermal treatment is required – Protein unfolding – Water binding – Protein-protein interactions – Water immobilization
Gelation z A gel is a continuous network of macroscopic dimensions immersed in a liquid medium exhibiting no steady-state flow z Denatured proteins z Thermal treatment is required – Protein unfolding – Water binding – Protein-protein interactions – Water immobilization
Gelation z Bound Water – Small portion tightly bound to proteins – Majority of water is capillary water – 3D network must be formed to entrain water z Factors affecting gel formation – °T – Protein concentration – pH – Salt concentration – Ca++ – Free [sulfhydryl] – Protein hydrophobicity
Gelation z Bound Water – Small portion tightly bound to proteins – Majority of water is capillary water – 3D network must be formed to entrain water z Factors affecting gel formation – °T – Protein concentration – pH – Salt concentration – Ca++ – Free [sulfhydryl] – Protein hydrophobicity
Gelation z Protein network – Balance between protein-protein and proteinsolvent interactions – Attractive and repulsive forces – Hydrophobic interactions (enhanced by high T) – Electrostatic interactions (Ca++ bridges) – H-bonding (enhanced by cooling) – Disulfide cross-links
Gelation z Protein network – Balance between protein-protein and proteinsolvent interactions – Attractive and repulsive forces – Hydrophobic interactions (enhanced by high T) – Electrostatic interactions (Ca++ bridges) – H-bonding (enhanced by cooling) – Disulfide cross-links