予備乳化を伴う膜乳化法を用いれば, 低い乳化エネルギーで単分散性の高いO/W型またはW/O型エマルションを生産性よく調製することができる. この方法では, さらに高濃度エマルション, 多相エマルション, 粒子凝集のない高融点油脂O/Wエマルションなど, 特徴的な性状の食品エマルションを調製することも可能である. 本報告では, このような予備乳化を伴う膜乳化法の興味ある特徴を紹介する.
予備乳化を伴う膜乳化法を用いる転相法で, 低濃度の予備乳化エマルションを転相させて高濃度のエマルションを得る. 実験で得られた最大濃度は, O/Wエマルションで約90%, W/Oエマルションで約85%であった. 平均細孔径1.0μmのPTFE膜を用いて, 平均粒径2.5μmの単分散性の高いW/O/Wエマルションを調製できた(粒子分散係数, α≒0.1). この場合の予備乳化W/O/Wエマルションの膜透過流束は, 負加圧0.3MPaで4～10m3/m2/h程度の値が得られた. W/O/Wエマルションを調製する際の内包率は, W/Oエマルションの粒径には影響を受けなかった. 膜乳化で得られたエマルションを再度膜透過させると, 効果的な粒径の微細化が起きた. 高融点油脂(融点=313K)を用いたO/Wエマルションを予備乳化を伴う膜乳化法で調製した場合には, 室温で数日間放置しても平均粒径に変化はなく, 液体状態を保っていた. このことは, 室温に放置しても油脂粒子の凝集が起きていないことを示している.The membrane emulsification method combined with preliminary emulsification enables us to prepare O/W or W/O type emulsions with narrow particle size distribution at high production rate without high mechanical stress. The method also prepares stable food emulsions with unique properties such as ultra-high concentration, multi-phase, solid fat particle in water without agglomeration and so on. This paper introduced an interesting feature of the membrane emulsification method combined with preliminary emulsification.
Highly concentrated emulsions were prepared from the low concentration pre-emulsified emulsions by the membrane phase inversion method. The maximum concentration obtained was ca. 90% for O/W emulsion, and ca. 85% for W/O emulsion. The W/O/W emulsions of very small particle (mean diameter, Dp ≒ 2.5 μm) with narrow particle size distribution (coefficient of variation, α ≒ 0.1) could be obtained using a PTFE membrane (mean pore size = 1.0 μm). The permeating flux of pre-emulsified W/O/W emulsion through the membrane was ca. 4~40 m3/m2/h at 0.3 MPa. The encapsulation efficiency was not affected by the particle size of W/O emulsions. Increasing passage times through membrane decreased effectively the particle diameter of emulsion. Solid fat (melting point: Tm ≒ 313 K) in water (O/W) emulsions prepared by the method were liquid state, and mean particle diameter (Dp ≒ 2.0 μm) was almost unchanged during standing for several days at room temperature. This indicated that no appreciable aggregation of fat particles in O/W emulsions was observed
