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Protein fouling is a critical problem for ultrafiltration. In this study, we adopted bovine serum albumin (BSA) as a model protein and polysulfone membrane as a typical ultrafiltration membrane. We then investigated the factors of the protein denaturation and aggregation, such as stirring shear stress and intermolecular exchange of disulfide during ultrafiltration, and discussed the BSA fouling mechanism. Fourier transform-infrared analysis revealed that magnetic stirring did not cause any difference in the secondary structural change of BSA gel-like deposits on the ultrafiltration membrane. BSA aggregates were collected from BSA gel-like deposits on the ultrafiltration membrane by centrifugation. Polyacrylamide gel electrophoresis in SDS analysis of BSA aggregates proved that the major binding of the BSA aggregates involved intermolecular disulfhydryl binding and that capping the free thiol group in BSA molecules with cysteine induced a remarkable decrease in the amount of the BSA aggregates during ultrafiltration. We concluded that one of the main factors in the BSA aggregation during ultrafiltration is the intermolecular exchange of disulfide through cysteinyl residue. We also found that the BSA aggregation caused a decrease in alpha-helix from 66% to 50% and an increase in beta-sheet from 20% to 36%, which was presumably because the cysteine residues associated with the intermolecular disulfide bonds had been located in alpha-helices.

Super-monodispersed oil-in-water (O/W) microspheres (MS) were produced using a microchannel (MC) emulsification technique. To investigate the effect of the surfactant on the behavior of the O/W-MS formation, the MS size and its distribution, various surfactants were used for the MC emulsification process. An MC plate with 8.9 µm equivalent diameter was employed. It was found that the super-monodispersed O/W-MS production depends on the type of surfactant used. When nonionic and anionic surfactants were used, supermonodispersed O/W-MS were produced, and the average droplet diameter was about 30 µm with a standard deviation less than 1 µm. For cationic surfactants, the super-monodispersed O/W-MS production was not successful, especially for the case where hydrophobic surfactant was dissolved in the oil phase. The results indicated that it is very important to maintain the hydrophilicity of the MC surface during the MC emulsification process. It is considered that the hydrophilic group of the anionic and nonionic surfactant was repulsed from the negatively charged MC surface so that the hydrophilicity of the MC surface was maintained. Otherwise, adsorption of the positively charged group of the cationic surfactant occurred on the MC surface which improved wetting of the MC surface and deteriorated the MC emulsification process. The analysis was supported by contact angle measurement.Paper no. S1182 in JSD 3, 285-293 (July 2000). KEY WORDS: Microchannel emulsification, monodispersed microspheres, surfactant effect. Microspheres (MS), which are emulsion cells or solid particles dispersed in a continuous phase, have been utilized in various industries such as foods, cosmetics, and pharmaceuticals. Emulsions are dispersed multiphase systems consisting of two or more almost mutually insoluble liquids, with the dispersed phase present in the form of droplets in a continuous phase (1). Using conventional methods of emulsion production, the emulsion droplets (or MS) are usually polydispersed over a wide range. Formation of MS with a narrow droplet size distribution is highly desirable, but in general is very difficult. Membrane emulsification is a relatively new technique that has the potential of reproducibly forming emulsions with a narrow droplet size (2-4). This method uses the pores of a microporous membrane to disperse the dispersed phase into the continuous phase by applying pressure. Recently Kawakatsu et al. (5) have proposed a novel microchannel (MC) emulsification technique for supermonodispersed MS production. The MC emulsification technique is based on the research of Kikuchi et al. (6 ,7), in which they developed a microscope video system and optically accessible MC formed in a single crystal silicon substrate for the observation of blood rheology and flow behavior of blood cells. For the MC emulsification technique, an MC plate was pressed close to an optically flat glass plate to form uniform-sized channels, and the dispersed phase was pressed through the channels to disperse regularly into the continuous ph...