Protein Functionality

FDSC400

Goals

• Hydrodynamic-Aggregation– Viscosity, Elasticity, Viscoelasticity– Solubility, Water holding capacity

• Hydrophobic- Surface Active– Emulsion and foam stabilization– Flavor binding

Concentration

Vis

cosi

ty

Dilute

Sem

i-di

lute

Con

cent

rate

d

rg

Hydrodynamic Functionality

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

Dough stretched

Dough released

Time

Length

+SO32-

Creep

Mechanisms of Link formation

• Hydrophobic (following denaturation or hydrolysis)

• Thiol-disulfide interchange

• Enzymic crosslinking

• Also consider repulsive effects (charge)

Water BindingWater 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

pH

1 2 3 4 5 6 7 8

Sol

ubili

ty /%

0

20

40

60

80

100

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

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electrostatic

(a magnification of the lamella between two touching bubbles or two emulsion droplets)

steric

Emulsion Stabilization

• Proteins adsorbed to surfaces can stabilize emulsions and foams by various mechanisms

• Proteins are often denatured on binding

Food Enzymes

• Biological catalysts• Proteins (can be

denatured)• Specific (can be

inhibited)G

reaction

Substrate

Product

intermediate

Enzyme stabilized intermediate

Polyphenol oxidase

• Founds in plans, animals and some microorganisms, requires Cu2+, O2

OH

CH3

OH

CH3

OH

OH

OH

O

O

[O]

[O]

ME

LA

NIN

S

phenol diphenol

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

-amylase(endo-splitting) glucoamylase

Highly viscous suspension of polymerized corn starch

105°CFructose

Glucose isomerase