A water-in-oil-in-water (W/O/W) multiple emulsion containing a hydrophilic substance, 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (PTSA), and a wall material in its inner and outer aqueous phases, respectively, was prepared by a two-step emulsification using a rotor/stator homogenizer, and was further homogenized with a high-pressure homogenizer. Maltodextrin or gum arabic were used as wall materials, and olive oil was used as the oily phase. The high encapsulation efficiency for PTSA (.0.9) was realized. The emulsion was spray-dried to produce microcapsules of W/O/W type. The efficiencies of the microcapsules prepared with maltodextrin and gum arabic were 0.82 and 0.67, respectively. Stability of the microcapsules was examined at 37 7C and 12%, 33% and 75% relative humidity. Microcapsules prepared with maltodextrin were more stable than those prepared with gum arabic.

Conditions for preparing W/O/W emulsions with a polymer in the aqueous phase as a possible entrapping agent to produce powdery multiple emulsions were investigated for food applications of W/O/W emulsions. The stability of these emulsions prepared using various types of emulsifiers was evaluated by the encapsulation efficiency of a hydrophilic marker molecule in the inner aqueous phase. Combinations of hexaglycerin polyricinoleate (Sunsoft 818SX) and soybean lecithin or gum arabic used in the first and second emulsification steps were suitable to prepare stable W/O/ W emulsions. Emulsions containingϾ10% (w/v) polymers in the outer aqueous phase were successfully prepared using these emulsifier pairs by adding the polymers to the emulsions after homogenization. Addition of polymer to the inner aqueous phase did not have a significant effect on emulsion stability in spite of expected alleviation of osmotic pressure difference between the inner and outer aqueous phases.

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W/O/W emulsions were prepared using low concentrations of emulsifiers in the oily and outer aqueous phases, and the formation of the emulsions were evaluated by the encapsulation efficiency of a fluorescent marker in the inner aqueous phase. W/O/W emulsions were produced even at low emulsifier concentrations, although the standard deviation of the encapsulation efficiency immediately after preparation became larger as the emulsifier concentration decreased. Long-term stability of the emulsions with no emulsifier was unsatisfactory, although emulsions with a lipophilic emulsifier only in the oily phase were stable for 30 days with a decrease in the encapsulation efficiency of less than around 5%. Emulsifier species also significantly affected the formation of W/O/W emulsions.