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Effect of emulsifier type and processing parameters on the preparation of stable water-in-oil-in-water (W1/O/W2) double emulsions

In order to achieve stable water-in-oil-in-water (W1/O/W2) double emulsions (DEs) prepared with sunflower oil and produced by high-pressure homogenization process using a Microfluidizer, the impact of different emulsifiers and their concentration, as well as emulsion processing conditions were examined. To study the efficiency of emulsifier type, sorbitan monooleate (Span 80), sorbitan trioleate (Span 85), polyoxyethylene sorbitan monooleate (Tween 80), polyglycerol polyricinoleate (PGPR) in W1/O, and polyoxyethylene sorbitan monolaurate (Tween 20) and whey protein isolates (WPIs) in W2 phase were examined in different concentrations. Additionally, different ratios of emulsion components, homogenization time and speed used for coarse emulsions preparation, pressures and number of cycles applied in microfluidization step were investigated. Emulsions were evaluated for their stability and particle size distribution and characterized morphologically using confocal microscopy. Among investigated emulsifiers, only PGPR produced stable W1/O emulsion, while emulsions prepared with other emulsifiers were destabilized in a very short time. The stability of W1/O emulsions containing PGPR, expressed as the transmission percentage against time was between 0.506-1.081 %/h, indicating high emulsion stability, with increasing PGPR concentration (4%, w/v) resulting with better emulsion stability. To obtain the most stable DEs, PGPR W1/O emulsions were mixed with W2 phase (40:60) containing WPIs and microfluidized for 1 cycle at 200 bars. The particle size of such obtained DEs varied from 322.27 to 539.70 nm. The obtained results highlight PGPR emulsifier as the most effective one for achieving stable nano-scale DEs, but indicate that further experiments are needed to define the optimal emulsion preparation conditions. Such prepared nanoemulsions could serve as effective delivery systems of bioactive food ingredients for potential food applications.

Double emulsions; Emulsifier type; Emulsion stability; PGPR

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