Coat formation of surface-active proteins on aqueous surfaces during drying

Effect of Diffusion on Component Segregation During Drying of Aqueous Solutions Containing Protein and Sugar

“…Nijdam et al [9] showed that BSA accumulated at the surface of their dried films, in a manner similar to the surface accumulation of BSA on spray-dried particles observed by Fäldt and Bergenståhl. [5] A BSA surface coverage of 48.5% was measured for films with bulk BSA concentrations ranging from 10.5 to 41.2% (db).…”

“…Because nonsegregation of these solutes was demonstrated experimentally by Nijdam et al, [9] for the sake of modeling, BSA and lactose were considered as a single homogenous component. Therefore, the system became binary, consisting of water and a single solute made up of BSA and lactose.…”

“…Other mechanisms to explain preferential surface accumulation of components include surface activity [7] and capture of relatively large immobile components (such as sodium caseinate and BSA) by the receding evaporative surface while small mobile components (such as lactose) diffuse away. [8] Nijdam et al [9] have measured depth concentration profiles within thin films of BSA and lactose that had previously been dried from their aqueous solutions at 80 C, a typical droplet temperature during spray drying. [10] The aim of that work was to determine whether concentration gradients in BSA and lactose had developed within the film during drying, which might then confirm the phenomenon of preferential accumulation of components at surfaces due to differential diffusion, as described by Kim et al [6] BSA surface activity was also considered as a possible mechanism of preferential surface accumulation, although Nijdam et al [9] excluded the mechanism of component capture by the receding evaporative surface from their film drying experiments.…”

“…[8] Nijdam et al [9] have measured depth concentration profiles within thin films of BSA and lactose that had previously been dried from their aqueous solutions at 80 C, a typical droplet temperature during spray drying. [10] The aim of that work was to determine whether concentration gradients in BSA and lactose had developed within the film during drying, which might then confirm the phenomenon of preferential accumulation of components at surfaces due to differential diffusion, as described by Kim et al [6] BSA surface activity was also considered as a possible mechanism of preferential surface accumulation, although Nijdam et al [9] excluded the mechanism of component capture by the receding evaporative surface from their film drying experiments. Drying of thin films rather than droplets was investigated in their study to enable analysis by (1) inverse microscope Raman spectrometry (IMRS) [11,12] to measure the depth concentration profiles through the entire film thickness at a spatial resolution of micrometers and (2) X-ray photoelectron spectroscopy (XPS) sputterdepth profiling to measure depth concentration profiles in the vicinity of the surface of each dried film at a spatial resolution of nanometers.…”

“…A drying model will be used to simulate film drying at 80 C in order to investigate whether moisture content gradients could develop within the film during drying at this temperature and thus elucidate why no significant BSA and lactose segregation was observed in the bulk of the film by Nijdam et al [9] In order to provide some measure of confidence in the drying model, it will first be partially validated with experimental moisture content profiles obtained using IMRS during film drying at 30 C. This temperature is within the operating limits of the optical lens used in the IMRS. The ultimate aim of this work is to determine whether the differential diffusion mechanism suggested by Kim et al [6] can adequately explain accumulation of low-diffusivity components such as proteins at aqueous interfaces during drying.…”