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Functional Properties of Proteins
The functional properties arise from a number of physical and chemical properties
and affect the behavior of proteins in food systems during processing, cooking, storage and consumption. In addition to this they are also influenced by other factors
such as pH, temperature, radiation or the presence of ions in foods. The functional
properties of proteins play an important role as they determine the applications of
particular type of protein in different systems. As food systems are usually complex
therefore selecting specific type of protein for a particular application will depend
upon its functionality. The functional properties depend upon the type of amino
acids and functional groups present in the particular amino acid and also depend
upon the interactions which are responsible for stabilizing the native structure of
protein molecule. The favorable interactions in protein molecules may be covalent,
hydrophobic, electrostatic, hydrogen bonds and ionic interactions. These interactions also determine the type of functionality of a protein in different food systems.
In general, several factors affect the functional properties of food proteins,
namely intrinsic factors such as amino acid sequence and composition, secondary
and tertiary structures, hydrophilic/hydrophobic character of the protein surface,
net charge and charge distribution and molecular rigidity/flexibility of the protein
and extrinsic factors such as pH, ionic strength, temperature and interactions with
other food components (Zhu and Damodaran 1994). It is important to note that
processing of foods may lead to structural modification of the native structure of the
protein reversibly (unfolding) or irreversibly (denaturation) depending upon the
processing conditions and technologies applied. Food, chemical and pharmaceutical industries rely upon these functional properties of proteins with the aim of
improving the stability of the formulations or developing novel foods. Some functional of proteins which are important from the technological point of view are
discussed below.
Solubility
Solubility is one of the most important properties of proteins since other functional
properties like emulsion activity, emulsion stability, water binding capacity, oil
binding capacity, foam capacity and foam stability are directly related to solubility
(Stefanović et al. 2017). Some researchers have even concluded that solubility is the
prerequisite for other functional properties. Solubility is also considered as the most
important applicable scale for denaturation and aggregation thus it is a good indicator of protein function. A number of factors which play a predominant role in solubility are amino acid composition and number of hydrophilic groups present in the
particular amino acid and the pH. Protein surface has a net charge that depends on
the number and identity of the charged amino acids, and also depends upon the
pH. For example at a specific pH the positive and negative charges will be balanced
and the net charge will be zero this pH is called the iso-electric point. Most of the
food proteins have iso-electric pH ranging from 3.5 to 4.5. A protein molecule has
N. A. Mir et al.
Functional Properties of Proteins
The functional properties arise from a number of physical and chemical properties
and affect the behavior of proteins in food systems during processing, cooking, storage and consumption. In addition to this they are also influenced by other factors
such as pH, temperature, radiation or the presence of ions in foods. The functional
properties of proteins play an important role as they determine the applications of
particular type of protein in different systems. As food systems are usually complex
therefore selecting specific type of protein for a particular application will depend
upon its functionality. The functional properties depend upon the type of amino
acids and functional groups present in the particular amino acid and also depend
upon the interactions which are responsible for stabilizing the native structure of
protein molecule. The favorable interactions in protein molecules may be covalent,
hydrophobic, electrostatic, hydrogen bonds and ionic interactions. These interactions also determine the type of functionality of a protein in different food systems.
In general, several factors affect the functional properties of food proteins,
namely intrinsic factors such as amino acid sequence and composition, secondary
and tertiary structures, hydrophilic/hydrophobic character of the protein surface,
net charge and charge distribution and molecular rigidity/flexibility of the protein
and extrinsic factors such as pH, ionic strength, temperature and interactions with
other food components (Zhu and Damodaran 1994). It is important to note that
processing of foods may lead to structural modification of the native structure of the
protein reversibly (unfolding) or irreversibly (denaturation) depending upon the
processing conditions and technologies applied. Food, chemical and pharmaceutical industries rely upon these functional properties of proteins with the aim of
improving the stability of the formulations or developing novel foods. Some functional of proteins which are important from the technological point of view are
discussed below.
Solubility
Solubility is one of the most important properties of proteins since other functional
properties like emulsion activity, emulsion stability, water binding capacity, oil
binding capacity, foam capacity and foam stability are directly related to solubility
(Stefanović et al. 2017). Some researchers have even concluded that solubility is the
prerequisite for other functional properties. Solubility is also considered as the most
important applicable scale for denaturation and aggregation thus it is a good indicator of protein function. A number of factors which play a predominant role in solubility are amino acid composition and number of hydrophilic groups present in the
particular amino acid and the pH. Protein surface has a net charge that depends on
the number and identity of the charged amino acids, and also depends upon the
pH. For example at a specific pH the positive and negative charges will be balanced
and the net charge will be zero this pH is called the iso-electric point. Most of the
food proteins have iso-electric pH ranging from 3.5 to 4.5. A protein molecule has
N. A. Mir et al.