1. Functional Properties

2. Proteins contribute significantly to the physical properties of
foodstuffs, especially
ability to build or stabilize gels,
foams,
doughs,
emulsions and
fibrillar structures.
Foaming, gelling, and emulsifying properties
Foaming Properties
Proteins act as foam-forming and foam-stabilizing
agents in various foodstuffs, e.g., in baked products,
sweets, desserts, and beer.

3. The properties of various proteins
serum albumin foams
ovalbumin does not.
Mixtures of proteins,
e.g., egg white, can be particularly effective. In that case, the globulins start the formation
of foam; ovomucin is important for its stabilization, and ovalbumin and conalbumin are
responsible for the heat-setting properties.
Foams are dispersions of gases in liquids.
Proteins stabilize such systems by forming flexible, cohesive films around the surface of
the gas bubbles.
whipping, interface surface denaturation
decrease of the surface tension
interfaces gas bubbles

4. Film formation and foamability of a protein molecule depends
on its diffusion rate and denatured.
These parameters in turn depend on
the molecular mass,
the surface hydrophobicity,
and the stability of the conformation
Foams collapse because large gas bubbles grow
stability of a foam depends on the stability of the protein film
and its permeability for gases.

5. The stability of the film in turn depends on the amount of adsorbed
protein and on the ability of the adsorbed protein to associate.
Surface denaturation exposes additional amino acid side-chains
that can participate in intermolecular interactions.
The stronger the cross-linking, the more stable is the film.
stabilizing protein is characterized by a low molecular mass, high
surface hydrophobicity, good solubility, a small net charge at the pH
of the food, and easy denaturability.
Foams are destroyed by lipids and organic solvents such as higher
alcohols

6. Egg yolk, prevents the whipping of egg white, at low concentrations.
The disturbance of protein association by the lecithins is responsible for that effect.

7. Enzymatic hydrolysis produces smaller molecules of a higher diffusion rate, better
solubility, and higher surface hydrophobicity.
The disadvantages are the lower film stability and the loss of heat coagulability.
The introduction of charged or neutral groups or a partial thermal denaturation (e.g., of
whey proteins) can also improve the desired properties.
strongly basic proteins (e.g., clupeines) increases the protein association within the films
and allows the foaming of lipid-containing systems.
Emulsifying Properties.
Emulsions are disperse systems of two or more immiscible liquids.
interfacial films and prevent the dispersed phase from coalescing.
Proteins are able to stabilize emulsions due to their amphipathic nature.

8. The emulsifying properties of a protein
adsorbability there,
deformability of interfacial tension (surface denaturation).
The diffusion rate
the temperature
molecular mass of the protein,
influenced by the pH and the ionic strength.
The adsorbability depends on
exposure of hydrophilic and hydrophobic groups,
the amino acid composition,
pH, ionic strength, and temperature.

9. THE STABILITY OF THE CONFORMATION DEPENDS ON
the molecular mass,
amino acid profile and number of intramolecular disulfide
bonds of the protein.
PROTEIN QUALITIES AS AN EMULSIFIER
oil-in-water low molecular mass,
a balanced amino acid composition in terms of charged, polar
and apolar sidechains,
good solubility in water,
marked surface hydrophobicity,
stable conformation

10. GEL FORMATION
Gels are disperse systems of at least two components in which a solid
phase (dispersed phase) forms a cohesive network in a liquid phase
(continuous phase).
Gels are characterized by their lack of fluidity and their elastic
deformability.
They are placed between solutions with repulsive forces between
molecules of the dispersed phase predominating,
and precipitates with strong intermolecular forces predominating.
two types of gels, the
‘polymeric networks‘ a
‘aggregated dispersions.
formed by gelatin or by polysaccharides such as
agarose or carrageenan.

11. Gels low concentration of polymer, transparency and fine texture.
Gel formation is started by adjusting to a suitable pH, by adding ions,
or heating followed by cooling.
aggregation takes place mainly via hydrogen bonds.
Polymeric networks are thermo-reversible
Examples of aggregated dispersions are the gels formed by globular
proteins after denaturation by heat.
The thermal unfolding of the protein exposes amino acid side-chains,
which can take part in intermolecular interactions.

12. Interfacial properties
Hydrophilic and hydrophobic moieties, proteins can adsorb
spontaneously at interfaces, and are often employed to stabilize
multiple phase foods such as foams and emulsions.
The interfacial adsorption of the protein results in conformational
changes which lead to a new free energy minimum and a reduction
of surface tension
The ability of the protein to adopt a different structure at the
interface depends on its molecular flexibility.

13. Flexible proteins,
β-casein, adsorb rapidly at the interface and adapt their structure,
Hydrophobic moieties are sheltered from the water phase,
flexible, hydrophilic parts of the structure instead protrude into the water phase.

14. Protein structures caused by interactions with polysaccharides

15. Binding properties of food proteins
ability of proteins to bind to hydrophobic molecules.
protein to assemble either spontaneously or to form aggregates
during processing
structures are tunable with processing, and the encapsulated labile
compounds (such as flavors, vitamins, drugs, polyphenols),
Bioactive molecules in particular areas of the gastrointestinal tract.
most proteins play a major role not only in structural scaffolding,

17. Protein Hydration
One of the essential components of food is water which effects the
rheological
and textural properties of foods
depending on its interaction with other food components such as
proteins and polysaccharides.
The interaction of water with proteins may effect the functional
properties of the proteins such as dispersibility, wettability, swelling,
solubility, thickening/viscosity, water-holding capacity, gelation,
coagulation, emulsification and foaming capacity

18. it is essential to analyze the hydration of proteins.
Water molecules bind to proteins through their charged groups (ion-dipole interactions);
backbone peptides groups: the amide groups of asparagine and glutamine;
hydroxyl groups of serine, threonine, tyrosine residues (dipole-dipole interactions);
nonpolar residues (dipole-induced dipole interaction, hydrophobic hydration).
dry protein interacts with water, the initial hydration occurs at the sites of ionizable
groups of protein.
Then, water clusters form near the polar and charged protein surfaces and hydration at
the polar surfaces is completed. The hydrophobic hydration of nonpolar

19. Water binding capacity (also called hydration capacity) of proteins defined as grams of
water bound per gram of protein when a dry protein powder is equilibrated with water
vapor at 90-95 % relative humidity.
Solubility
Solubility of proteins depends on the equilibrium between protein-protein and
protein-solvent interactions.
High solubility of a protein increases its functionality and usage in the food production.
Hydrophobic and ionic characteristics of the proteins are the major factors that affect the
solubility.
Hydrophobic interactions decrease the solubility because of the promotion of protein-
protein interactions while ionic interactions increase the solubility by promoting protein-
water interactions

20. Proteins are classified into four categories
according to their solubility as
, (1) albumins; soluble in water at pH 6,6 (e.g. serum albumin, ovalbumin);
(2) Globulins;soluble in dilute salt solution at pH 7,0 (e.g. glycinin, phaseolin);
Glutelins; soluble only in acid (pH 2,0) and alkaline (pH 12,0) solutions (e.g. wheat
glutelins);
(3) Prolamins; soluble in 70% ethanol (e.g. zein, gliadins).

22. Flavor Binding
Flavor is one of the important characteristics of the sensory properties of the
foods.
Although proteins are odorless they can bind flavor compounds.
Proteins bind flavor compounds tightly, retain them during processing of foods,
In dry conditions proteins bind flavors with van der Waals interactions,
hydrogen bonding, and electrostatic interactions.
In liquid or high moisture products, proteins bind flavor through hydrophobic regions on
the protein surface.
Oilseed proteins and whey proteins carry undesirable flavors and this limits their food
Applications.

23. Viscosity
The viscosity of a solution is related to its resistance to flow under an
applied
force (or shear stress).
Viscosity or consistency of the products is very important for the
consumer acceptance of several liquid and semisolid-type foods (e.g.
soups, beverages).
High-molecular-weight polymers such as proteins greatly increase
viscosity.
The viscosity behavior of proteins is affected by several variables
including size, shape,
protein-solvent interactions, hydrodynamic volume and flexibility in
the hydrated state.

24. Dough Formation
Food proteins, especially wheat proteins, have ability to form a
viscoelastic dough suitable for making bread and other bakery
products.
The formation of dough and its characteristics stem form proteins.
Gluten in cereals is the major protein for dough formation.
The dough structure is based on extensive three-dimensional
network of gluten protein sub-units joined together by disulfide
cross-links

25. Gluten is a mixture of gliadin and glutenins proteins and its amino
acid composition affects the functionality of gluten in the dough.
The high glutamine and hydroxyl amino acid residues responsible
for the gluten water binding properties whereas cysteine and
cystine residues have functions in the polymerization of gluten
proteins due to sulfhydryl-disulfide interchange reactions

26. determines the antioxidative properties of proteins or peptides. The correct positioning
in the peptide sequence is also a very important factor effective on antioxidant activity
(Rajapakse et al. 2005, Chen et al. 1996). It was reported that the position of histidine,
proline, leucine, and glutamic acid in the chains of antioxidative peptides is effective on
their radical scavenging activities. For example, the peptides having proline at the
Nterminus
more effectively prevents oxidation of linoleic acid than peptides having
proline at the C-terminus (Chen et al. 1996). Also, peptides having histidine residues at
the N-terminus show higher metal chelating activity than peptides having histidine at
the C-terminus (Chen et al. 1998).
By modification, it is possible to enhance the antioxidant activity of proteins.
For example, it was reported that Maillard reaction with polysaccharides may increase
the antioxidant activity of proteins by improving their hydrophilic/hydrophobic balance
(Nakamura et al. 1998). The antioxidant activity