Comparative study of the stability of multiple emulsions containing a gelled or aqueous internal phase

• Stable multiple emulsions prepared with internal gelled droplets.
• Simple method to produce small (<500 nm) alginate droplets.
• Gelation of internal water droplets reduces droplet size due to reduced recoalescence.
• Emulsions stable to changes in temperature, shear and salt.

Water in Oil in Water (WOW) multiple emulsions have, for many years, been studied in order to utilise their functionality in food and pharmaceuticals, for reduced fat formulation, drug delivery and taste masking applications. However, their complex structure is susceptible to a broader range of instabilities than conventional emulsions. In this study we investigate the role of different emulsifiers and a simple, novel approach to gel the internal aqueous droplets to improve the stability to heat, shear, and the presence of salt. Changes in salt concentration can be detrimental to multiple emulsions, as this will induce swelling or shrinkage of the internal water droplets. Polyglycerolpolyricinoleate (PGPR) was the preferred low HLB emulsifier, and its presence dominated the stability of the WOW emulsions, irrespective of the high HLB emulsifier. However, lecithin was found to be the most stable high HLB emulsifier to heating. Gelling the internal water droplets with either alginate or carrageenan reduced the size of the water droplets, probably due to reduced recoalescence rates. The multiple Gel in Oil in Water (GOW) emulsions were more stable to the addition of up to 1 wt% salt to the external phase than WOW emulsions. In addition, the presence of xanthan in the external phase further improved the stability to the addition of salt. Therefore GOW emulsions show potential to be used in a realistic food processing environment, showing stability to shear, temperature and changes in salt concentration.

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