title: Coat formation of surface-active proteins on aqueous surfaces during drying.
abstract: Segregation of the protein bovine serum albumin (BSA) and lactose in thin aqueous films during drying was investigated by examining the composition of the dried films using inverse micro Raman spectroscopy (IMRS) and X-ray photoelectron spectroscopy (XPS) sputter-depth profiling. The composition was uniform through the thickness of the dried films except within a 10nm region at the exposed surface where BSA had accumulated, most likely due to its surface activity. The thickness of the BSA layer was similar to the diameter of a BSA molecule, which suggests that a single monolayer of BSA adsorbed at the exposed surface. The BSA surface concentration of the dried films was constant over a wide range of BSA bulk concentrations, indicating that the aqueous surface became saturated with BSA during drying. The BSA surface layer of order 10nm was significantly thinner than the film thickness of order 10 μm, which implies that BSA formed a surface coating rather than a shell, and thus lent no structural rigidity to the film.
authors.affiliation: Chemical and Process Engineering Department, University of Canterbury, Private Bag 4800, Christchurch, New Zealand. Electronic address: justin.nijdam@canterbury.ac.nz.
authors.forename: J
authors.initials: J
authors.lastname: Nijdam
authors.affiliation: Institute for Applied Materials (IAM), Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: V
authors.initials: V
authors.lastname: Trouillet
authors.affiliation: Institute of Thermal Process Engineering, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Kachel
authors.affiliation: Institute of Thermal Process Engineering, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Scharfer
authors.affiliation: Institute of Thermal Process Engineering, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Schabel
authors.affiliation: Institute of Thermal Process Engineering, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Kind
mesh_terms: D000327:Adsorption; D000818:Animals; D002417:Cattle; D003890:Desiccation; D004339:Drug Compounding; D008565:Membrane Proteins / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D056951:Photoelectron Spectroscopy; D012710:Serum Albumin, Bovine / Q000737:chemistry*; D013059:Spectrum Analysis, Raman
chemical_list: D008565:Membrane Proteins; D012710:Serum Albumin, Bovine
keywords: Diffusion; Microencapsulation; Segregation; Spray drying