The powder characteristics of bovine somatotropin and casein spray-dried from laboratory, pilot and production spray-dryers were investigated. The powder characteristics examined included particle size distribution and morphology; bulk density; and flowability as measured by angle of repose, compressibility index and shear cell indices. Morphology classification showed internal voidage, blowholes, expanded, smooth and folding for somatotropin and casein spray-dried from the various spray-dryers. Particle size distributions of the bovine somatotropin and casein were unimodal and skewed. As the drying-chamber size of the spray-dryer increased, the particle sizes of both somatotropin and casein increased from mean volume diameters of 6-8 p using the laboratory and pilot spray-dryers to 13-24 p when using the production size spray-dryers. Spray-dried bovine somatotropin and casein had bulk densities of 0.090 to 0.195 g/cm3. Three flowability tests showed casein and somatotropin spray-dried from the different spray-dryers exhibited poor flow which could result in pharmaceutical manufacture challenges. The morphology and flowability of the two spray-dried proteins remained the same when comparing material produced from all four spray-dryers. However, the mean volume diameter, particle size distribution and bulk density did vary which might change critical product characteristics during scale-up. In general, similar morphology, particle size distributions, flowability and bulk densities were observed when comparing spray-dried casein and bovine somatotropin produced from the same model spray-dryer. Casein is recommended as a model protein for powder characterization during spray-drying and early formulation manufacture process development when adequate quantities of the recombinant protein are not available. 1705

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