《食品化学 Food Chemistry》课程教学课件（讲稿，英文版）Protein Functionality

Protein Functionality

Protein Functionality

Classification Protein must interact with other components of the food system z Hydration properties – Water absorption/retention; Wettability; Swelling; Adhesion, Dispersibility, Solubility, Viscosity z Protein-Protein Interactions – Gelation, Dough/fiber formation z Surface properties – Emulsification, Foaming

Classification Protein must interact with other components of the food system z Hydration properties – Water absorption/retention; Wettability; Swelling; Adhesion, Dispersibility, Solubility, Viscosity z Protein-Protein Interactions – Gelation, Dough/fiber formation z Surface properties – Emulsification, Foaming

Water binding z Factors influencing hydration – Protein concentration – pH – T – Ionic strength – Other compounds

Water binding z Factors influencing hydration – Protein concentration – pH – T – Ionic strength – Other compounds

Solubility z Extraction and Purification z Good Index for potential applications of proteins – Degree of insolubility – Impaired ability for gelation, emulsification and foaming – Important in food beverages z Markedly and irreversibly reduced when heating is involved z Main advantage – Permits rapid and extensive dispersion – Facilitates protein diffusion

Solubility z Extraction and Purification z Good Index for potential applications of proteins – Degree of insolubility – Impaired ability for gelation, emulsification and foaming – Important in food beverages z Markedly and irreversibly reduced when heating is involved z Main advantage – Permits rapid and extensive dispersion – Facilitates protein diffusion

Viscosity z Reflects its resistance to flow z Main factor influencing viscosity behavior – Apparent diameter of the dispersed molecules – Diameter depends on: z Intrinsic characteristics of protein z Protein-solvent interactions z Protein-protein interactions

Viscosity z Reflects its resistance to flow z Main factor influencing viscosity behavior – Apparent diameter of the dispersed molecules – Diameter depends on: z Intrinsic characteristics of protein z Protein-solvent interactions z Protein-protein interactions

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 protein￾solvent 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 protein￾solvent interactions – Attractive and repulsive forces – Hydrophobic interactions (enhanced by high T) – Electrostatic interactions (Ca++ bridges) – H-bonding (enhanced by cooling) – Disulfide cross-links

Emulsification z Thermodynamically unstable mixtures of immiscible liquids z Protein stabilized emulsions – Diffuse to interface – Unfold – Expose hydrophobic groups – Interact with lipid z Adsorb at interface and contributes to the physical and rheological properties to prevent droplet coalescence

Emulsification z Thermodynamically unstable mixtures of immiscible liquids z Protein stabilized emulsions – Diffuse to interface – Unfold – Expose hydrophobic groups – Interact with lipid z Adsorb at interface and contributes to the physical and rheological properties to prevent droplet coalescence