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Protein Functionality
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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
t y
Dilute
Sem
i-dilu
te
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
-
-
---
- ---
-
-
--
-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]
MEL
AN
INS
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 starch105°C
Fructose
Glucose isomerase
