Coat formation of surface-active proteins on aqueous surfaces during drying

Area of Science:

• Biochemistry
• Materials Science
• Surface Chemistry

Background:

• Understanding the behavior of proteins and sugars in thin films during drying is crucial for various applications, including food science and pharmaceuticals.
• Bovine serum albumin (BSA) is a common model protein used in biophysical and materials science studies.
• Lactose is a disaccharide frequently used in pharmaceutical formulations and food products.

Purpose of the Study:

• To investigate the segregation and distribution of bovine serum albumin (BSA) and lactose within thin aqueous films during the drying process.
• To determine the location and extent of BSA accumulation at the film surface.
• To understand the implications of BSA surface adsorption on the overall film structure.

Main Methods:

• Inverse micro Raman spectroscopy (IMRS) was employed to analyze the composition of dried films.
• X-ray photoelectron spectroscopy (XPS) sputter-depth profiling was used to determine the elemental composition through the film thickness.
• Analysis focused on the compositional changes within the top 10nm of the dried films.

Main Results:

• The dried films exhibited uniform composition throughout their thickness, except for a ~10nm surface layer enriched with BSA.
• BSA accumulation at the surface is attributed to its inherent surface activity.
• The BSA surface layer thickness, comparable to a single BSA molecule's diameter, suggests monolayer adsorption.
• BSA surface concentration reached saturation over a broad range of initial BSA concentrations.
• The BSA surface layer was significantly thinner than the overall film thickness, indicating a coating rather than a structural shell.

Conclusions:

• BSA preferentially segregates to the exposed surface of aqueous films during drying, forming a thin, saturated monolayer.
• This BSA surface coating does not impart structural rigidity to the overall film.
• The findings have implications for controlling film properties and stability in processes involving BSA and lactose mixtures.