In contrast to model solutions of protein, food systems have a complex composition that contains proteins, polysaccharides, lipids, minerals, etc., of different types
and mixes at different concentrations and ratios. The presence of molecules other
than proteins in the medium, such as small solutes (specific ions, amino acids, fatty
acids, etc.), strongly affects their assembly process [9–12]. The assembly process is
also affected when working with mixtures of proteins [13–15]. These parameters
constitute putative, still underestimated, means for controlling the characteristics and
functionalities of new supramolecular structures. All these parameters must be
considered for the interpretation of data on the protein assembly process. In fact,
combining the large diversity in protein structure (stability, repartition of hydrophobic and hydrophilic patches, net charge, localisation of charged group onto the
protein surface, etc.) and in medium composition offers endless possibilities for
protein self-assembly into supramolecular structures. In these conditions, the control
of supramolecular structure formation becomes a real challenge, though examples
from biological systems inform us that food technology has just entered this new
scientific area.
Prediction of protein assembly needs for its perfect control an understanding
of the physicochemical parameters affecting protein–protein and/or protein–
aggregates and/or aggregates–aggregates interactions at different length scales,
from molecular to nano- and mesoscopic, and at different time scales. One of the
key issues for controlling the formation of supramolecular structures with defined
size and shape is to identify the initial events that promote the later stages of the
process of protein assembly. Having proteins with well-characterised molecular
structure (identification of residues and atoms accessible to the solvent and available for protein–protein interaction) is helpful for understanding and predicting the
mechanism of protein assembly at a molecular level [16]. Forces and energies
developed at a higher range scale could be different since intrinsic properties of
aggregates change throughout the progress of the assembly. Identifying the type
and intensity of inter-protein and inter-supramolecular structure interactions acting
simultaneously and/or sequentially in both space and time constitutes important
knowledge for understanding protein behaviour in complex systems [17].
Induced assemblies and spontaneous assemblies (self-assemblies) are two distinctive routes to the formation of supramolecular structures. Induced assemblies
occur when proteins are destabilised consecutively to an induced unfolding and/or
hydrolysis that triggers protein assemblies. They are obtained under physicochemical conditions that are different from physiological conditions, i.e., under
elevated temperatures and/or extreme pH conditions, by changing solvent quality,
etc. [18–23]. Induced assemblies are often irreversible. In contrast, protein selfassemblies dictated by thermodynamics involve the spontaneous and hierarchical
association of the proteins into ordered supramolecular structures without the
contribution of external energy input and/or denaturing agents. The driving forces
for self-assembly involve either attractive intermolecular interactions or an indirect
entropy contribution resulting from the release of counter-ions and water molecules
[24, 25]. Self-assembly phenomenon is widespread in nature and is the basis of
numerous biological functions (structure, regulation, transport, protection, etc.).
Apart from mimicking nature, using the self-assembly potential of proteins for the
Spontaneous Assembly and Induced Aggregation of Food Proteins
69
and mixes at different concentrations and ratios. The presence of molecules other
than proteins in the medium, such as small solutes (specific ions, amino acids, fatty
acids, etc.), strongly affects their assembly process [9–12]. The assembly process is
also affected when working with mixtures of proteins [13–15]. These parameters
constitute putative, still underestimated, means for controlling the characteristics and
functionalities of new supramolecular structures. All these parameters must be
considered for the interpretation of data on the protein assembly process. In fact,
combining the large diversity in protein structure (stability, repartition of hydrophobic and hydrophilic patches, net charge, localisation of charged group onto the
protein surface, etc.) and in medium composition offers endless possibilities for
protein self-assembly into supramolecular structures. In these conditions, the control
of supramolecular structure formation becomes a real challenge, though examples
from biological systems inform us that food technology has just entered this new
scientific area.
Prediction of protein assembly needs for its perfect control an understanding
of the physicochemical parameters affecting protein–protein and/or protein–
aggregates and/or aggregates–aggregates interactions at different length scales,
from molecular to nano- and mesoscopic, and at different time scales. One of the
key issues for controlling the formation of supramolecular structures with defined
size and shape is to identify the initial events that promote the later stages of the
process of protein assembly. Having proteins with well-characterised molecular
structure (identification of residues and atoms accessible to the solvent and available for protein–protein interaction) is helpful for understanding and predicting the
mechanism of protein assembly at a molecular level [16]. Forces and energies
developed at a higher range scale could be different since intrinsic properties of
aggregates change throughout the progress of the assembly. Identifying the type
and intensity of inter-protein and inter-supramolecular structure interactions acting
simultaneously and/or sequentially in both space and time constitutes important
knowledge for understanding protein behaviour in complex systems [17].
Induced assemblies and spontaneous assemblies (self-assemblies) are two distinctive routes to the formation of supramolecular structures. Induced assemblies
occur when proteins are destabilised consecutively to an induced unfolding and/or
hydrolysis that triggers protein assemblies. They are obtained under physicochemical conditions that are different from physiological conditions, i.e., under
elevated temperatures and/or extreme pH conditions, by changing solvent quality,
etc. [18–23]. Induced assemblies are often irreversible. In contrast, protein selfassemblies dictated by thermodynamics involve the spontaneous and hierarchical
association of the proteins into ordered supramolecular structures without the
contribution of external energy input and/or denaturing agents. The driving forces
for self-assembly involve either attractive intermolecular interactions or an indirect
entropy contribution resulting from the release of counter-ions and water molecules
[24, 25]. Self-assembly phenomenon is widespread in nature and is the basis of
numerous biological functions (structure, regulation, transport, protection, etc.).
Apart from mimicking nature, using the self-assembly potential of proteins for the
Spontaneous Assembly and Induced Aggregation of Food Proteins
69