Protein Functionality

FUNCTIONAL PROPERTIES OF FOOD PROTEINS Hydration Solubility Viscosity Gel formation Texture Dough formation Emulsification Foaming Aroma binding Interaction with other food components The proteins have a major effect on the structure and sensory quality of numerous foods in fresh and processed conditions, for example on the consistency and texture of meat and meat products, milk and cheese, pasta and bread. Food quality most often depends on the structural and physico-chemical quality of the protein components. Some of these functional properties are: hydration, solubility, viscosity, gel formation, texture, dough formation, emulsification, foaming, aroma binding and interaction with other food components.

Goals Hydrodynamic-Aggregation Hydrophobic- Surface Active Viscosity, Elasticity, Viscoelasticity Solubility, Water holding capacity Hydrophobic- Surface Active Emulsion and foam stabilization Flavor binding

Hydrodynamic Functionality Dilute Semi-dilute rg Viscosity Concentrated Concentration

Viscosity A property of LIQUIDS Viscosity is the resistance to flow. The amount of energy you need to expend to get a given flow rate. Stress (force per unit area) is proportional to rate of strain (i.e., flow rate) Particles of any type in a fluid will increase its viscosity Large, well hydrated polymers contribute most to viscosity

Elasticity A property of SOLIDS Elasticity is the force to achieve a given percentage change in length Stress (force per unit area) is proportional to strain (fractional deformation) An elastic material must have some solid-like network throughout the structure The more load bearing structures the more elastic The more inter-structure links the more elastic

Viscoelasticity Many materials simultaneously show solid and liquid like properties If they are stretched they will partly and slowly return to their original shape Elastic solids would completely recover Viscous liquids would retain their shape

Creep Dough stretched Dough released +SO32- Length Time

Mechanisms of Link formation Hydrophobic (following denaturation or hydrolysis) Thiol-disulfide interchange Enzymic crosslinking Also consider repulsive effects (charge)

Water Binding Gel contains pores Water can flow out of the pores If the gel contracts it may expel liquid SYNERESIS Due to closer association of protein with protein Casein gels are very porous structures and water can easily flow out of them, either if an external pressure is applied or if the casein strands are allowed to fold into a tighter conformation and so squeeze the water out. Breaking casein strands or increasing the attractive forces can lead to syneresis. The amount of syneresis in cheese curd is a major determinant of the moisture content of the finished cheese. Cutting the curd allows some realignment of the gel structure and some moisture is squeezed out.

Solubility

Hydrophobic/Surface Functionality Emulsion stabilization Foam destabilization Flavor binding

Whey vs. Casein Dense, ordered globular proteins 2D Gel Loose, disordered, flexible chains Loop-train-tail model

Emulsion Stabilization Proteins adsorbed to surfaces can stabilize emulsions and foams by various mechanisms Proteins are often denatured on binding electrostatic steric - - - - - - - - - - - - - - (a magnification of the lamella between two touching bubbles or two emulsion droplets)

Food Enzymes Biological catalysts Proteins (can be denatured) Specific (can be inhibited) intermediate Enzyme stabilized intermediate DG Substrate Product reaction

Polyphenol oxidase Founds in plans, animals and some microorganisms, requires Cu2+, O2 diphenol phenol MELANINS diphenol catechol

Lipoxygenase Catalyzes peroxidation of fatty acids Abstracts an H., allows reaction with O2, free radicals produced Leads to rancidity and flavor Co-oxidations Bleaching flour Thiols Vitamins

Amylase Starch Dextrins Glucose Fructose a-amylase (endo-splitting) glucoamylase Starch Dextrins Glucose Highly viscous suspension of polymerized corn starch Glucose isomerase Fructose 105°C