Spray protein solutions

Spray drying, employed preferentially for inexpensive enzymes on a mass scale, evaporates water by spraying the protein solution through a nozzle at high temperature, utilizing the Bernoulli effect. As contact times are short (on the order of less than 1 s), the enzyme is not deactivated. Not much modeling has been performed on this operation. 

The two main variations of the antisolvent technique are (1) bubbling of SCF CO2 into a protein solution continuum (generally referred to as GAS) and (2) spraying a protein solution into a SCF CO2 continuum (generally known as PCA/SAS). The other techniques listed previously are subsets of these. 

In addition to UV/IR-MALDI, there is another possibility for bringing protein ions into the gas phase electrospray ionization (ESI). Figure 7.7 illustrates how the method works. The proteins are not gasified via incorporation into an evaporable matrix but by spraying the protein solution as finest droplets. Weak acids serve as ionization helpers, and organic solvents as spraying helpers. Acetonitrile/water 50 50 with 0.1% acetic acid is a typical carrier solution. Salts and detergents disrupt ESI and have to be removed. For this, Troxler et al. (1999) use small return-phase columns (Cg, elution with TFA, acetonitrile). 

Spray drying of protein solutions can result in substantial inactivation. Proteins have the tendency to denature and undergo irreversible aggregation during various steps of spray drying for various stress reasons. These reasons are shown schematically in Fig. 6.31 (Lee, 2002) and will be discussed in the following. 

The loss of native protein by adsorption to surfaces is problematic in biopharma-ceutical applications. Proteins are able to adsorb at liquid/gas, liquid/solid and liquid/liquid interfaces due to their amphiphilic property. Adsorption stress can occur in the vessel of the feed protein solution, and at the liquid/gas interface between the sprayed droplets and the hot air. Adsorption to the vessel wall is assumed to be practically negligible, whereas the adsorption at the liquid/gas interface may lead to substantial degradation because of the strong increase in the liquid/gas... 

J. Chandrapala, B. Zisu, M. Palmer, S.E. Kentish, M. Ashokkumar, Sonication of milk protein solutions prior to spray drying and the subsequent effects on powders during storage. J. Food Eng. 141, 122-127 (2014)... 

The SAS methods have been used for preparing a variety of particles and fine powders from proteins, pharmaceuticals, pigments, polymers, and even explosives. For example, Debenedetti and coworkers used a continuous-flow, supercritical antisolvent process to prepare fine powders of trypsin, lysozyme, and insulin proteins (58-60). In the preparation a protein solution in dimethyl-sulfoxide (DMSO) was sprayed through a small orifice into supercritical CO2. The particles had diameters ranging from 1 to 5 p,m. The biological activity of the micrometer-sized powders was nearly the same as that of the starting materials. The method has also been used in the processing of pharmaceutically important compounds, such as salmeterol xinafoate (61), sulfathiazole (62), and methylprednisolone and hydrocortisone acetate (41). Kitamura et al. used the... 

Finally, protein-based fibrils can be formed and may be used to increase the stability of the interfacial film in spray-dried microcapsules. In concentrated protein solutions depending on the environmental conditions (pH, ionic strength, temperature) and the process conditions (e.g. shear), fibril structures or spherical aggregates may occur as a result of hydrolysis and denaturation [41,42]. In literature the formation of fibrils using p-lactoglobulin and whey protein isolate is described. These amyloid-like anisotropic aggregates are formed at pH values below the isoelectric point (pH 2.0. 0) and several hours of heating (at or above 80 °C)... 

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