This page looks at the way the different amino acids will contribute to the functionality of proteins, that is, how the proteins will behave in a food. For example, in the diagram below, one sees that the ability to gel, bind water, and become more soluble as the charge decreases. A protein is more likely to contribute to foam and emulsify as the hydrophobic nature decreases.

The following table gives another look at this. Again look how the structure of the protein and hydrophobicity contributes to foaming. These same factors improve emulsification. Note how solubility decreases as hydrophobicity of the number of amino acids increases. The increases in alpha helix, beta-sheets will also decrease solubility.

Contribution of Charge Frequency, Hydrophobicity and Structural Factors to Functionality of Proteins.

Functional Property	Charge Frequency	Hydrophobicity	Structural Factors
Emulsification	(-)	+ surface	+
Fat binding	(-)	+ surface	-
Foaming	-	+ total	+
Heat coagulation	-	+ total	+
Solubility	+	-	-
Water holding	+	-	?

( )contributes to a lesser extent, surface refers to surface hydrophobicity, total refers to total hydrophobicity, + positive contribution, - negative contribution.

Denaturation are the changes in structure which cause changes in function. There is a distinct change in natural properties of the protein when the unique spatial arrangement of the helix of polypeptide chain is altered. Changes observed can be described explicitly by the operations used to study them. During denaturation some of the forces holding the chains together break, causing protein to uncoil and unfold. New bridges formed.

Any change in the structure is denaturation. Thus, this site will use the term denaturation to refer to the process, or sequence of processes whereby the protein molecule undergoes intramolecular change or rearrangement.

Denaturants

Change in the protein molecule may be brought about by the physical, chemical(acid, salt) and/or biological(enzyme) action of denaturants. In the production of meat products, the action of heat and chemical denaturation are of main importance. The denaturant of immediate concern to most food scientists is heat denaturation; however, chemical denaturation can not be disregarded. A part of chemical denaturation may be due to added ingredients or through the result of thermal action. In meat products, the separation of pH and temperature are interdependent denaturants and separation of the two is difficult.

Getting down to it, denaturation of protein will change its colloidal state, it may increase solubility, decrease solubility, undergo gelation and/or increase viscosity.

Gelation There has been a review of in the food systems section of this site of the basic theories of gelation. Not all gels are protein, however, a good many of them are. This protein-protein (particle to particle) interaction includes association, aggregation, polymerization, precipitation, flocculation, and coagulation. The theory of gelation translates into vegetable protein gels, milk gels, starch gels, vegetable gum gels, egg gels and meat gels, all complex food sources. In all cases, we have either a carbohydrate gel or a protein gel, each with similarities and each with differences. However, irregardless, a protein gel is a complex protein-protein and protein-water interaction with a stable gel formed when this is in balance. Gelation A dominant example of increased viscosity by protein is in the production of a stirred custard. The protein denaturation will increase the viscosity of the mixture. Other examples are dependent upon the presence of hydrophilic amino acids on the protein. These hydrophilic amino acids may have an increasing water shell which increases viscosity.

GLOSSARY

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AGGREGATION in proteins refers to to the formation of large complexes from the proteins.

amino acid
amino group
amorphous
amphiphilic
amphoteric elements
coagulate
coagulation
covalent bond
enzyme
FIBROUS PROTEINS are proteins composed of polypeptide chains assembled among the straight axis such as a helix. Examples are collagen, elastin, fibroin, and keratin.

FLOCCULATION in proteins refers to random aggregation reactions in the absence of denaturation.

FUNCTIONALITY is any property, omitting nutritional attributes, that influences an ingredient's usefulness in foods. These are primarily those functional properties which influence the sensory (texture, color, appearance, flavor) characteristics of a food.

gel
GELATION in proteins is when denatured molecules aggregate to form the ordered three dimensional network.

GLOBULAR proteins are proteins composed of one or more polpeptide polymers folded upon themselves as globs or spheres.

peptide
peptide linkage
polymerization
PRIMARY STRUCTURE in protein refers to the sequential order of amino acids in a protein.

protein hydrolysate
proteinase
SECONDARY STRUCTURES relate to the three-dimensional organization of the polypeptide chain.

STRUCTURAL PROTEINS are present in tissues such as bone, cellular membranes, internal organs, intracellular organelles, muscle, and skin. They are generally fibrous proteins such as collagen, elastin, and keratin. TERTIARY STRUCTURES relate to the three-dimensional organization of the polypeptide chain.

QUATERNARY STRUCTURE refers to the geometric arrangement among various polypeptide chains. These are chains that may be loosely bonded by hydrogen, sulfide, and salt-bridges.

Types of Denaturation
Heat

Enzymes

Chemicals (acids, phenolics, salts)

Mechanical or Agitation

Ultraviolet light

Pressurization

In each case the changes is evidence by either viscosity, gelation, hydration, or hydrolysis.

REVIEW

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Does the protein in the following foods primarily contribute to texture, color or flavor of the food product?

Egg custard

Mayonnaise

Cheese

Foam Cake

Spinach

Describe and draw a diagram of the basic structure of an amino acid.

What is the significance of the "R" group on amino acids?

Define the following:


___ term given to an organic compounds that have both basic and acidic characteristics. ___ point where the carboxyl and the amine groups are ionized and the charge is neutral. ___ two "R" groups of protein which are hydrophilic. ___

Define the following:


___ point at which an protein is least stable. ___ is the protein structure that is a combination of amino acids in a proper sequence by means of the peptide bonds. ___ is the protein structure which includes the folding of the coiled chain or chains and is thought to influence the degree of hydration association with the "R" groups. ___ Term for linkage between two amino acids that connects the amino group of one and the acid (carboxyl) group of the other. ___ Where is any protein least stable? change from the native state. ___ two dominant ways that proteins are colloidally dispersed. ___ The name of the change (reaction phenomenon) that occurs when the protein is changed to free amino acids.

What is protein denaturation?

Define the following terms.


___ term referring to heat destruction of pathogenic microorganisms. ___ term for process involving heating raw milk at a sufficiently high temperature for a specified time to destroy pathogenic bacteria.

What is the primary denaturing agent for each of the following?


formation of clabber for large curd cottage cheese

preparation of curd for large curd cottage cheese

direct formation of clabber for small curd cottage cheese

preparation of cheddar cheese from clabber

formation of foam for angel food cake


preparation of unbaked foam for souffle.

preparation of unbaked meringue

formation of foam for angel food cake

baking of prepared souffle

formation of a baked meringue

preparation of whipped cream toppings

formation of baked custard

preparation of an unflavored yogurt

curdled milk in "southern" dry-cured ham

preparation of yogurt gel

frying of egg

Describe the differences and/or similarities between the following terms:
syneresis vs. weeping
coagulation vs. clabber
coagulation vs. curdling
gelation vs. clabber

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Updated: Wednesday, October 24, 2007.