W1/O/W2 double emulsions stabilised by fat crystals – Formulation, stability and salt release

Water/oil (W1/O) emulsions containing fat crystals have been incorporated into an aqueous phase containing 1% na-caseinate as emulsifier to create stable water/oil/water (W1/O/W2) double emulsions. The W1/O primary emulsion was stabilised exclusively with monoglyceride and triglyceride crystal “shells”, and contained 30% W1 aqueous phase as well as KCl.The stability of the double emulsions was monitored over the course of 6 weeks. It was found that, providing some salt or sugar were present in the W2 aqueous phase, emulsions retained their double structure – although coalescence between double emulsion globules occurred and creaming was observed. KCl encapsulated in the W1 phase of the primary emulsion was only slowly released to the W2 continuous aqueous phase: 20% within 6 weeks. This release is due to the damage caused to the fat crystal shells during the secondary emulsification step used to create the double emulsion structure.

Graphical abstractDouble emulsions show good stability against KCl release when W1 crystal shells are smooth (low osmotic pressure gradient), but release salt rapidly when crystals protrude from interface (high (positive) osmotic pressure gradient).Figure optionsDownload full-size imageDownload high-quality image (112 K)Download as PowerPoint slideResearch highlights► Double emulsions can be produced using only fat crystals (mono- and triglyceride) to stabilise the primary emulsion ► The fat crystals have sintered to form “shells” around the primary W1 aqueous droplets, to give a special form of Pickering stabilisation ► These double emulsions retain their structure and encapsulated salt over the course of at least 6 weeks when the osmotic pressure gradient is matched between the two aqueous phases ► The sintered crystal “shells” were more stable to compressive rather than tensile loading ► Salt release is likely to occur through “cracks” in the “shells” sustained during the secondary emulsification step.