Effect of Emulsifier Type on Droplet Disruption in Repeated Shirasu Porous Glass Membrane Homogenization Goran T. Vladisavljevic ´,* ,† Jeonghee Surh, ‡ and Julian D. McClements ‡ Institute of Food Technology and Biochemistry, Faculty of Agriculture, UniVersity of Belgrade, P.O. Box 127, YU-11081 Belgrade-Zemun, Serbia & Montenegro, and Department of Food Science, Biopolymer and Colloids Research Laboratory, UniVersity of Massachusetts, 100 Holdsworth Way, Amherst, Massachusetts 01003 ReceiVed December 16, 2005. In Final Form: March 7, 2006 The influence of various emulsifier types (anionic, nonionic, and zwitterionic) on the mean particle size, transmembrane flux, and membrane fouling in repeated membrane homogenization using a Shirasu porous glass (SPG) membrane has been investigated. Oil-in-water (O/W) emulsions (40 wt % corn oil stabilized by 0.06-2 wt % sodium dodecyl sulfate (SDS) or 0.1-2 wt % Tween 20 at pH 3 or 0.5-2 wt % -lactoglobulin (-Lg) at pH 7) were prepared by passing coarsely emulsified feed mixtures five times through the membrane with a mean pore size of 8.0 µm under the transmembrane pressure of 100 kPa. The flux increased as the number of passes increased, tending to a maximum limiting value. The maximum flux for the Tween 20-stabilized emulsions (5-47 m 3 ‚m -2 ‚h -1 ) was smaller than that for the SDS-stabilized emulsions (29-60 m 3 ‚m -2 ‚h -1 ) because less energy was needed for the disruption of a SDS- stabilized droplet due to the lower interfacial tension. The mean particle size after five passes was 4.1-6.8 and 6.4-8.7 µm for 0.1-2 wt % SDS and Tween 20, respectively. The flux in the presence of -Lg was much smaller than that in the presence of SDS and Tween 20, which was a consequence of more pronounced membrane fouling, due to the protein adsorption to the membrane surface. After five passes through the membrane, the fouling resistance in the presence of 2 wt % -Lg (1.1 × 10 10 1/m) was 2 orders of magnitude higher than that for 0.5 wt % Tween 20 and an order of magnitude higher than the membrane resistance. If a clean membrane was used in the fifth pass, a 2-fold reduction of the fouling resistance was observed. Introduction Conventional emulsification devices such as high pressure valve homogenizers generally use inhomogeneous extensional and shear forces and high energy inputs of 10 6 -10 8 J‚m -3 to rupture droplets. 1,2 As a result, they generate emulsions with relatively small droplet sizes but wide particle size distributions. Further, homogenization is often followed by a considerable temperature elevation as a result of the poor energy utilization. Membrane emulsification is a relatively new emulsification technology, aimed at achieving precise control of the particle size distribution over a wide range of mean droplet sizes. 3 This technique is particularly useful for producing multiple emulsions 4 and monodisperse solid microparticles (microspheres and mi- crocapsules) 5 because of its effectiveness in preparing droplets with very narrow particle size distributions at low energy inputs. In “direct membrane emulsification”, a pure liquid (the disperse phase) is forced through the membrane pores into another immiscible liquid (the continuous phase), and the small droplets are formed in situ at the membrane-continuous phase interface. 6-8 In “premix membrane emulsification” (membrane homogeniza- tion), coarsely emulsified feeds are forced through the membrane, and the small droplets are formed by reducing the size of the large droplets in preexisting emulsions. 9,10 The major advantages of this approach are that emulsions with higher droplet concentrations can more easily be produced, and higher trans- membrane fluxes can be achieved, but at the expense of a higher extent of droplet polydispersity. The degree of monodispersity can be improved by passing the emulsion through the membrane a number of times. 11-14 The repeated membrane homogenization was originally developed for the production of multilamellar lipid vesicles (liposomes) using track-etch polycarbonate filters, which contain almost identical cylindrical pores. 15 In this process, the coarse liposome suspension is passed under moderate pressure repeatedly (usually 10 times) through filters with progressively smaller pore sizes, which leads to a gradual break up of the large vesicles into smaller ones. 16 The most commonly used microporous membrane for emul- sification is made of a special kind of CaO-Al 2 O 3 -B 2 O 3 - SiO 2 -type porous glass called Shirasu porous glass (SPG). 3 The major advantages of this membrane are that it can be fabricated with mean pore sizes in a wide interval between 0.1 and 20 µm, * Corresponding author. Tel: (+381) 11 2615 315/327. Fax: (+381) 11 199 711. gtvladis@afrodita.rcub.bg.ac.yu. † University of Belgrade. ‡ University of Massachusetts. (1) McClements, D. J. Food Emulsions: Principles, Practices, and Techniques, 2nd ed.; CRC Press: Boca Raton, FL, 2005; p 259. (2) Joscelyne, S. M.; Tra ¨gårdh, G. J. Membr. Sci. 2000, 169, 107. (3) Nakashima, T.; Shimizu M.; Kukizaki, M. AdV. Drug DeliVery ReV. 2000, 45, 47. (4) van der Graaf, S.; Schroe ¨n, C. G. P. H.; Boom, R. M. J. Membr. Sci. 2005, 251, 7. (5) Vladisavljevic ´, G. T.; Williams, R. A. AdV. Colloid Interface Sci. 2005, 113, 1. (6) Vladisavljevic ´, G. T.; Schubert, H. J. Membr. Sci. 2003, 225, 15. (7) Vladisavljevic ´, G. T.; Schubert, H. Colloids Surf., A 2004, 232, 199. (8) Vladisavljevic ´, G. T.; Schubert, H. J. Dispersion Sci. Technol. 2003, 24, 811. (9) Suzuki, K.; Fujiki, I.; Hagura, Y. Food Sci. Technol. Int. Tokyo 1998, 4, 164. (10) Shima, M.; Kobayashi, Y.; Fujii, T.; Tanaka, M.; Kimura, Y.; Adachi, S.; Matsuno, R. 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