Preparation of multiple emulsions using SPG membranes: Factors influencing droplet size distribution, dispersed phase flux and encapsulation yield

摘要

Membrane emulsification (ME) involves the permeation of pure dispersed phase through a porous membrane into continuous phase (direct ME) or the passage of pre-emulsion through the membrane (premix ME [1]). In direct ME, fine droplets are directly formed at the pore openings. In premix ME, large droplets of a premix are disrupted into fine droplets inside the pores. The most suited membrane for ME is a Shirasu porous glass (SPG) membrane developed by Nakashima and Shimizu [2]. Preparation of multiple W_1/O/W_2 emulsions using multi-pass premix ME has been studied in this work. The oil phase was 5 wt. percent PGPR dissolved in soybean oil. The inner aqueous phase contained 2 wt. percent Ca (II)-EDTA as a marker for the determination of the encapsulation yield and 5 wt. percent glucose as the osmotic additive. The outer aqueous phase contained 0.5 wt. percent Tween 80, 1 wt. percent sodium alginate, and 5 wt. percent glucose. The primary W_1/O emulsion was prepared by means of a homomixer at 24,000 rpm. The W_1/O emulsion was then mixed with the outer aqueous phase by means of a stirring bar to prepare a W_1/O/W_2 premix. The premix was homogenized by permeation through the SPG membrane with a mean pore size of 10.7 mu m and an effective membrane area of 3.75 cm~2. Centrifugal cells with a mean pore size of 0.2 mu m were used to separate the prepared W_1/O drops from the outer aqueous phase. The Ca content in the filtrate was measured by the ICP method. The total Ca content in the internal droplets was found by breaking a prepared emulsion with acetone. The encapsulation yield was determined as the percentage of Ca which was left in the internal droplets after emulsification.