Influence of water-soluble poly -ols on globular protein functionalities
The objective of this study was to better understand the impact of model polyol cosolvents (glycerol and sorbitol) on the physicochemical properties and functionalities of a model globular protein (β-lactoglobulin) at neutral pH. The influence of the cosolvents on the protein's properties in aqueous solutions (solubility, aggregation, molar volume, molar compressibility and thermal denaturation temperature), at interfaces (surface and interfacial tension), in emulsions (emulsion formation and stability) and in gels (gel strength, appearance and water holding capacity) were studied. The results showed that both glycerol and sorbitol increased the thermal stability of β-lactoglobulin, increased the attraction between protein molecules and altered protein functionality, but by different amounts. These results can be mainly attributed to the steric exclusion of sorbitol and glycerol molecules from the protein molecule surface. However, glycerol molecules can preferentially accumulate around hydrophobic parts on the protein surface, which decreases the thermal stability of the protein, thereby partially compensating for the steric exclusion effect. Thus, sorbitol had more impact on the thermal stability of the globular protein than glycerol. Overall, the impact of the cosolvents on globular protein functionality can be attributed to (i) the increase in the thermal stability of the globular protein, (ii) an alteration of the molecular interactions between protein molecules, and (iii) an increase in the viscosity of the intervening medium. These results can be used to design protein-containing food materials that have improved functional properties.