Damage of proteins at the air/water interface: Surface tension characterizes globulin interface stability.

In the present study, we aimed to see what circumstances may cause protein damage at air/water interface and reveal the correlation between the surface properties of protein solution and the interface stability. The surface hydrophobicity and β-sheet of protein were determined by exogenous fluorescent probes, and the changes in the spatial structure of proteins were characterized by steady-state fluorescence spectroscopy. The surface tension was determined by the plate method, and such value was used to establish the correlation with the hydrophobicity and structure of the protein. Moreover, degree of aggregation in the presence or absence of Hofmeister salt in protein solution was investigated. There was a significant correlation between the surface tension and hydrophobicity of the protein solution (P < 0.05). The surface tension and structure of the protein also showed a significant correlation under the induction of pH (P < 0.05). Furthermore, when the protein was induced by the air/water interface, the surface tension, hydrophobicity, and structure of proteins were correlated, and protein aggregation was increased. When the additive induced a decrease in the surface tension of the protein solution, the protein aggregation was promoted. These findings provided valuable insights into the relationship between surface tension of the protein solution and interfacial stability and paved the way for future pre-formulation studies of therapeutic proteins.