Influence of internal water phase gelation on the shear- and osmotic sensitivity of W/O/W-type double emulsions

• Internal aqueous phase gelation was proven using low-resolution NMR T2-relaxometry.
• W/O/W-droplets with small diameter and high internal water content were produced.
• Internal water phase gelation reduced shear-sensitivity of the double emulsion.
• Internal water phase gelation influenced osmotic behavior of the double emulsion.

It has already been hypothesized and in some cases proven that gelation of the internal water droplets of W/O/W-type double emulsions might allow the application of a higher shear in the second emulsification step while maintaining a high internal water content. In this contribution, thermal denaturation of a concentrated whey protein isolate solution, which is used as the internal water phase, was investigated. Low-resolution NMR T2-relaxometry measurements (using a CPMG-sequence) clearly showed that this thermal treatment effectively gelled the internal water phase. Using this approach, double emulsion droplets with a small average diameter (D43 of about 5 μm) and narrow particle size distribution were produced while a high internal water content was maintained. Moreover, our results indicated that gelation could not prevent osmotic shrinking of the double emulsion droplets upon dilution in hypertonic solution. However, gelation of the internal water phase clearly reduced the degree of osmotic swelling of the double emulsion droplets upon hypotonic dilution. However, this effect is probably due to droplet-globule coalescence occurring at lower internal water volume increases in case the internal water phase is gelled.

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