Surface composition of spray-dried particles of bovine serum albumin/trehalose/surfactant

Purpose. To characterize via electron spectroscopy for chemical analysis (E SCA) the surface of spray-dried particles of trehalose plus a protein (bovi ne serum albumin). Additionally, to show how and why the addition of a surf actant reduces protein adsorption, and by this mechanism could reduce prote in instability during spray-drying. Methods. Aqueous solutions of trehalose plus bovine serum albumin (bSA) wer e spray-dried with increasing concentrations of surfactant. The surface com position of the dried particles was examined using ESCA. Results. The presence of bSA, trehalose, and surfactant could be detected q uantitatively in the particle surface. In the absence of surfactant the bSA had a large surface excess concentration (determined via its N atoms). Inc reasing concentration of polysorbate 80 reduced the surface excess of bSA i n a concentration-dependent manner. At high polysorbate 80 concentration (5 mg/ml) the bSA could no longer be detected in solid surface. Using sodium dodecyl sulfate it was shown that the reduction in surface concentration of the protein is accompanied by a simultaneous increase in surface concentra tion of the surfactant. Neither surfactant fully covers the surface at the point of complete protein exclusion. Conclusions. ESCA provides a direct, quantitative measure of the surface co mposition of spray-dried trehalose/protein/surfactant particles. Surfactant reduces protein adsorption at the water/air-interface. This appears to be a result of complex formation with the surfactant within the bulk spray sol ution.