Preparation of water-in-oil-in-water emulsions by low frequency ultrasound using skim milk and sunflower oil

Double emulsions of water-in-oil-in-water (W1/O/W2) type were prepared in skim milk using 20 kHz ultrasound. Ultrasonic emulsification provides a simple and quick yet effective protocol by which double emulsions can be created using low amounts of surfactant. The fat displacement and shelf stability of the emulsions were found to be dependent on the amount of sonication power delivered during the dispersion of the W1/O emulsion into skim milk. Acoustic intensity was manipulated to control the size distribution of the outer shell of the emulsion droplets to a range similar to that of fat globules in unhomogenized whole milk. The encapsulation yield (proportion of W1/O droplets subsequently encapsulated within the W1/O/W2 double emulsion) varied from 5 to 35%. The variation could be due to coalescence/aggregation of water phase droplets within the initially formed W1/O emulsion. The resultant double emulsion droplets were found to be relatively stable over 7 days. However, a source of instability was found to be the leakage of entrapped aqueous phase from the inner to the outer phase with storage time. Phase separation was primarily observed for double emulsions prepared using high W1/O loading (20% w/w) and low ultrasonic power delivery (