Study of the dynamical behavior of sodium alginate/myoglobin aqueous solutions: A dynamic light scattering study

In the last years, protein/polysaccharide systems have received increasing research interest since they play an essential role in stabilizing food formulations, pharmaceutical preparations and so on. In this study, the diffusive properties of both sodium alginate and sodium alginate/myoglobin water solutions were characterized by dynamic light scattering. By analyzing the effects of concentration, pH and ionic strength on the diffusion coefficient, it emerged that sodium alginate forms aggregates which diffuse as pH sensitive rigid spheres. In the presence of the protein, the polysaccharide is less prone to self-aggregation favoring the formation of more solvent exposed protein/polysaccharide aggregates. These aggregates resulted to be both pH and ionic strength sensitive since their formation arises from a balance between coexisting repulsive and attractive interactions that are strongly influenced by the environmental conditions. By Fourier-Transform Infrared spectroscopy we evidenced the structural changes that take place in myoglobin during the protein-alginate complex formation. The observed increase in the solvent exposed extended chain conformation supported the hypothesis of a more open conformation adopted by the polysaccharide-protein complex with a consequent reorganization of hydrogen bonding.