Résumé
Proteins have multiple functionalities such as structuring ability (aggregation-gelation, coacervation) and sur-face properties (emulsification, foaming, solid surface adsorption). Our working hypothesis is that protein sol-ubility is the key to controlling these functionalities, through the Gibbs free energy of cavity creation (ΔGC), one of component of solvation free energy. In order to better rationalise the solvation process of plant pro-teins, we used the Scaled Particle Theory, SPT, to compute ΔGC and chose to work with proteins known for their particularly low solvation rate in water, sorghum kafirin.Kafirin, sorghum’s storage proteins, are known for their high content of hydrophobic amino acids (60-65 %) in comparison to other prolamins, like wheat gluten proteins or corn zeins (about 50-55%). The resulting high hydrophobicity and self-assembling properties of kafirins lower their solubility.We aim to compute the energy needed to solvate these hydrophobic proteins by focusing on the structure of solvent molecules around non polar residues based on cavity formation. Cavity creation is pointed out to be an entropy driven process. In this study, we calculated ΔGC by SPT [1], [2], [3], using the characteristics of kafirin, in tert-butanol, isopropanol, ethanol and water.Following an experimental design, we showed that ΔGC is one of the main factors influencing kafirin solubility, along with temperature. The ΔGC for the different solvents tested varies from 0.157 to 0.317 kJ.mol-1.Å-2. The solvents’ ranking of cost of cavity creation is ΔGC(tert-butanol) < ΔGC(Isopropanol) < ΔGC(Ethanol) < ΔGC(Water). Finally, solvents with high packing density and low density fluctuations, decrease the energy of cavity creation resulting in increased protein solubility.References:[1] Graziano, G. (2006). Scaled Particle Theory Study of the Length Scale Dependence of Cavity Thermodynamics in Different Liquids. The Journal of Physical Chemistry B, 110(23), 11421‑11426. https://doi.org/10.1021/jp0571269[2] Graziano, G. (2015). The Gibbs energy cost of cavity creation depends on geometry. Journal of Molecular Liquids, 211, 1047‑1051. https://doi.org/10.1016/j.molliq.2015.08.034[3] Pierotti, R. A. (1976). A scaled particle theory of aqueous and nonaqueous solutions. Chemical Reviews, 76(6), 717‑726. https://doi.org/10.1021/cr60304a002