This document discusses various functional properties of proteins important in food systems, including emulsification, hydration, viscosity, gelation, texturizability, foaming, and emulsification. It explains how protein solubility, size, structure, and interactions with other components influence these properties. Specific examples are given of proteins that demonstrate different functionalities like thickening, water binding, and foam formation.

1. FOOD CHEMISTRY
MODULE 2 PROTEINS
1
Presented by
Dr. A.Surendra Babu, Ph.D., PDF
Assistant Professor,
Dept. of Food Science and Technology,
SOAS, MRUH

2. Functional properties
• Functionality of food proteins is defined as those physical and
chemical properties which affect the behaviour in food system during
processing, storage, preparation and consumption.
• Typical functional properties include emulsification, which is
important in sausage type processed meats, hydration and water
binding, which are critical in doughs & meat products , viscosity ,
important for beverage
e.g. liquid instant breakfast, gelation, required in marshmallous

3. • Protein functionality - size, shape, amino acid composition and
sequence, net charge and distribution of charges, hydrophobicity
ratio, secondary, tertiary and quaternary structure, molecular
flexibility / rigidity, and ability to interact / react with other
components.

4. Solubility
• The functional properties of protein are often affected by protein
solubility and these most affected are thickening, foaming,
emulsifying and gelling.
• Insoluble protein has very limited uses in food.
• The solubility of a protein is the thermodynamic manifestation of the
equilibrium between protein –protein and protein solvent interaction

5. • Hydrophobic interaction promote protein – protein interaction and
result in decreased solubility
• Ionic interaction promote protein –water interactions and result in
increased solubility.

6. Based on solubility characteristics, proteins are classified into three
categories.
• Albumins are those that are soluble in water at pH 6.6 (e,g. Serum
albumin, ovalbumin & - lactalbumin)
• Globulins are those that are soluble only in acid (pH 2) and alkaline
(pH 12) solutions (e.g. wheat glutins)
• Prolamins are those soluble in 70% ethanol (e.g. zein and gliadins ).

7. Protein hydration
• Water is an essential constituent of foods.
• The rheological & textural properties of depend on the interaction of
water with other food constituents, especially with macromolecules,
such as proteins and polysaccharides.
• Water modifies the physiochemical properties of proteins.
• For example, the plasticizing changes their glass transition
temperature

8. • Many functional properties of protein such as dispersibility, swelling,
solubility, thickening, viscosity, water holding capacity, gelation, etc., depend
on water protein interactions.
• The ability of protein to bind water - acceptability to these foods.
• Water molecules bind to several groups proteins.
• These include charged groups / ionic dipole interaction, backbone peptide
groups, the amide groups of Asn & Gln, hydroxyl groups of Ser, Thr, and Tyr
residues and nonpolar residues (dipole induced dipole interaction,
hydrophobic hydration).

9. • Protein exhibit the least hydration at their isoelectric pH.
• Above & below the isoelectric pH, because of the increase in the net
charge & repulsive forces, protein swells and binds more water.
• The water binding capacity of most protein is greater at pH 9-10 than
at any other pH.
• The water binding capacity of protein generally decrease as the
temperature is raised, because of decreased hydrogen bonding &
decrease hydration of ionic groups which may leads to aggregation of
the protein.

10. Viscosity
• The consumer acceptability of several liquid & semisolid type foods
(e.g. gravies, soups, beverages etc.) depends on the viscosity or
consistency of the product.
• Many proteins absorb water and usually swell, thereby causing
changes in hydrodynamic properties that are reflected in thickening
and increase in viscosity.
• Viscosity & rheological properties related to flow are usually
measured on dispersions, slurries or pastes, using viscometer with
various spindle types.

11. • The viscosity of a solution related to its resistance to flow under an
applied force (or shear stress).
• For an ideal solution, the shear stress (i.e. force per unit area, F/A) is
directly proportional to the shear rate (i.e., the velocity gradient b/w
the layers of the liquid ,dv/dr).
• This is expressed as
• Fluids that obey this expression are called Newtonians fluids

12. • Viscosity is influenced by solubility and swelling properties of
protein.
• Highly soluble, non-swelling proteins posses low viscosity (e.g.
albumins, globulins),
• Soluble proteins with high, initial swelling show a concentration
dependent viscosity, e.g. sodium caseinate.
• Proteins with limited swelling capacity (Soy sodium proteinate) exert
high viscosity at relative low concentration.

13. Gelation
• A gel is an intermediate phase between a
solid a liquid.
• Technically, it is defined as a substantially
diluted system which exhibits no steady state
flow.
• Protein gels are composed of three
dimensional matrices or networks of
intertwined, partially associated,
polypeptides, in which water is entrapped.

14. • This transformation is facilitated by heat, enzymes or divalent cations
under appropriate conditions.
• Typically protein gels are coagulated egg white, soybean toffee, milk
casein curds & the myofibrillar gels by heating saline soluble meat or
fish protein.
• The ability of protein to form a gel & provide a structurally matrix for
holding water, flavours, sugars & food ingredients is useful in food
application

15. Texturizability
• The texture of foods is a critical property in determining their
acceptance in fact mouthful & bite characteristics are vital properties
of many foods.
• Proteins are the basic on structure in several foods, e.g. gelatine gels,
egg white, the myofibrils in meats & the curd of cheese.
• Hence, the capacity of protein to be texturized i.e. The ability to form
structure, chewiness & fibrosity is a functional property that is
assuming increasing importance.

16. • Texturization of proteins can be understood as the creation of a three-
dimensional structure to substitute partially or totally other proteins
(meat analogues) or lipids (fat substitutes) in traditional foodstuffs.
• Typical structures are fibres, shreds, chunks, bits, slices, films and granules.
• Protein texturization generally involves a first denaturation step
followed by the re-organization and orientation of the partially or
totally unfolded proteins by extrusion, rolling/spreading.
• The final step is the binding and stiffening of the organized protein
structure.
• Extruded fiber proteins are extracted directly from plants such as
soybeans or legumes

18. Foaming property
• Foaming or whipping i.e. the capacity to form stable foams with air
is an important functionality of protein in several products viz. food
cakes, sponge cakes, varies whipped topping, icings, fudges, nougats
etc.
• Foaming properties included whippability and foam ability.
• Foaming power measure, the increase in volume, upon the
introduction of a gas into a protein solution or dispersion.

19. • The percent of the expansion of ice cream achieved from the amount of air
incorporated into the product during the freezing process.
• An overrun of 50% means that it has expanded 50%

20. Emulsification
• Emulsification is the process of dispersing two or more immiscible
liquids together to form a semistable mixture.
• In food applications, these two liquids generally consist of an organic
(oil) phase and an aqueous (water) phase that is stabilized by the
addition of a food-grade emulsifier (surfactant).
• Proteins have been shown to stabilize emulsions by forming a
viscoelastic, adsorbed layer on the oil droplets, which form a physical
barrier to coalescence.