Functional Properties of protein PDF

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Functional Properties of protein...

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Food Chemistry-1 (IIIrd Year, Vth Semester) Functional Properties of protein

Organoleptic •

Proteins affect the sensory properties of food, i.e., •

Appearance;

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Texture (sols, gels, foams, emulsions, extruded pieces);

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Color (via browning reactions); and

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Flavor (via browning reactions and sulfide elimination reactions, via proteolysis, and by entrapment and binding of both desirable and undesirable flavors).

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Color, odor, flavor, and texture are key attributes of new proteins that determine whether they can be used in many products.

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Off-flavors constitute problems with many food proteins, e.g., soy, casein, peanut, fish, single cell, and leaf proteins-

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Usually this results from the presence of small amounts of lipids in these preparations.

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enzymatic (lipoxygenase) or chemical oxidation of the lipid components

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The nitrogenous components can also impart flavors, e.g., amino acids, peptides, and nucleotides.

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Protein derivatives, such as peptides and amino acids, possess a variety of flavor effects, e.g., the bitter taste of leucine rich peptides; the sweet taste of glycine, alanine, and the dipeptide, aspartyl phenylalanine methyl ester; and the glutamyl peptides, which effectively mask bitter flavors.

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Several flavors are generated from proteins by heating.

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Besides as a source of flavor, proteins bind flavors.

Solubility Several functional properties, such as thickening, foaming, emulsification, and gelation, of proteins are affected by protein solubility. Solubility of a protein is fundamentally related to its hydrophilicity/hydrophobicity balance. Thus, the amino acid composition of a protein inherently affects its solubility characteristics. Because solubility of a protein is a manifestation of the differences in the energetics of protein-protein and protein-solvent interactions. The average hydrophobicity of amino acid residues and charge frequency are the two most important factors that determine solubility of proteins:  The lower the average hydrophobicity and the higher the charge frequency, the higher the solubility. However, the solubility characteristics of proteins should be related to composition of the protein's surface (and not necessarily to its overall amino acid composition) and the thermodynamics of its interaction with the solvent.  Surface hydrophobicity and surface hydrophilicity characteristics of a protein's surface are the most important factors that affect its solubility characteristics. Factors: pH: Protein solubility in aqueous solutions is dependent on pH. At pH values above and below the isoelectric pH, proteins carry a net charge; electrostatic repulsion and ionic hydration promote solubilization of the protein. For most proteins, minimum solubility occurs at the isoelectric pH, where the electrostatic repulsion and ionic hydration are minimum and hydrophobic interaction between surface nonpolar patches is maximum.

Salts The salt affect the solubility of proteins in two different ways, depending on the physicochemical characteristics of the protein surface. Generally, at low ionic strength (...