Spray-drying is an effective, efficient means of producing peptide/protein-loaded powders suitable for pulmonary delivery. In addition, fine powders of proteins have application in other delivery systems (e.g., implantable pumps). If the correct formulation and spray-drying conditions can be identified, then a product can be obtained with a high yield and having a large fine-particle dose. Spray-drying is therefore a realistic alternative to the widespread practice of air-jet milling used to produce powders of low molecular-weight actives for inhalation. Indeed, air-jet milling should probably be avoided with peptides or proteins, because of possible problems of physical instability and inactivation. Apart from these considerations, spray-drying is also a suitable technique for embedding sensitive peptides or proteins in stabilizing excipients (“carriers”) such as disaccharides or amino acids.
In a study, the efficiency of drying carrier, whey protein isolate (WPI) was evaluated during spray-drying of honey. No powder was recovered when pure honey was spray-dried. Honey powders were successfully obtained (powder recovery >50%) by adding WPI alone at a ratio of Honey:WPI ratio of 70:30. The mechanisms of such a significant effect of WPI on spray-drying of honey are attributed to the preferential migration of protein to the droplet/air interface and the limited inward movement of protein during moisture evaporation, in conjunction with excellent skin-forming properties of protein upon drying. Powders' moisture content, water activity, and hygroscopicity were negligibly influenced by carriers.
Other carrier agents such as maltodextrins, gum Arabic, waxy starch, and microcrystalline cellulose, when introduced into the feed solution, influence the properties and stability of the powder. Crystalline and amorphous forms of the same material powder show differences in particle size, particle shape, bulk density, physicochemical properties, chemical stability, water solubility, hygroscopicity, flow properties and compatibility.