Encapsulation stability of duplex emulsions prepared with SPG cross-flow membrane, SPG rotating membrane and rotor-stator techniques—A comparison

Food grade duplex W1/O/W2 emulsions were prepared using three different techniques: SPG cross-flow membrane, SPG rotating membrane and high-shear mixer. The primary W1/O emulsion had sodium chloride encapsulated in the inner aqueous droplets as a marker compound. Duplex emulsion droplet size and salt encapsulation were both investigated by modifying the emulsification conditions inherent for each technique; cross-flow velocity (CFV) and trans-membrane pressure (TMP) for the cross-flow membrane, rotational velocity (RV) and TMP for the rotating membrane, and mixing time for the high-shear mixer.

Emulsion droplet size was shown to increase with TMP and to decrease with both CFV and RV. Minimum droplet size obtained (∼12 μm) was similar for all three emulsifying techniques, which suggests that at high shear stresses, the minimum droplet size is determined primarily by the decrease in the interfacial tension.

It was also shown that the amount of salt released during storage depends on the emulsification technique (8–20% for the cross-flow membrane, ∼13% for the high-shear mixer and ∼8% for the rotating membrane). The differences in salt release were explained in terms of emulsions droplet size and interfacial properties of adsorbed surfactant molecules. The unexpected high amount of salt released by duplex emulsions produced by the cross-flow membrane was associated with the magnitude and duration of shear forces, which act on duplex droplets during semi-batch emulsification.