Abstract
Water-in-oil-in-water (W1/O/W2) emulsions (double emulsions) have often been used for the encapsulation of bioactive compounds such as anthocyanins. Instability of both anthocyanins and double emulsions creates a need for a tailored composition of the aqueous phase. In this work, double emulsions with a gelled internal water phase were produced and monitored over a 20-day storage period. The effect of the electrolyte phase composition (varying electrolyte components, including adipic acid, citric acid, and varying concentration of potassium chloride (KCl)) on anthocyanin and double emulsion stability was analysed using colour analysis, droplet sizing, and emulsion rheology. The effect of electrolytes on colour retention was shown to differ between the primary W1/O emulsion and the secondary W1/O/W2 emulsion. Furthermore, droplet size analysis and emulsion rheology highlighted significant differences in the stability and structural behaviour of the emulsions as a function of electrolyte composition. In terms of colour retention and emulsion stability, a citrate-buffered system performed best. The results of this study highlight the importance of strict control of aqueous phase constituents to prevent anthocyanin degradation and maximise double emulsion stability. Additional experiments analysed the effect of pectin chemistry on the anthocyanin colour retention and leakage, finding no conclusive difference between the unmodified and amidated pectin.
Highlights
Anthocyanins are a class of naturally occurring polyphenolic compounds responsible for the vibrant blue, red, and purple colours of many fruits and vegetables, which have been used as a natural colourant in the food industry
Several studies have shown that inclusion of anthocyanin molecules in the internal aqueous phase of a double emulsion can protect them from changes in pH [11], temperature [12], and during simulated mouth and gastric digestion [13,14,15,16]
The results of this study demonstrate the significant differences in anthocyanin and emulsion stability arising from the electrolyte phase composition in single and double emulsions
Summary
Anthocyanins are a class of naturally occurring polyphenolic compounds responsible for the vibrant blue, red, and purple colours of many fruits and vegetables, which have been used as a natural colourant in the food industry (where it is given the food colourant code E163 [1], and is authorised for use in the European Union, Australia, andNew Zealand, and can be found in common supermarket products such as baked goods, chocolates, and energy drinks). Encapsulation methods are routinely employed to protect anthocyanins and other pigments [9] to preserve their beneficial properties during food production and storage. The composition and properties of the two aqueous phases can be altered to allow for better stabilisation and protection of the contents encapsulated within the internal water droplets. Several studies have shown that inclusion of anthocyanin molecules in the internal aqueous phase of a double emulsion can protect them from changes in pH [11], temperature [12], and during simulated mouth and gastric digestion [13,14,15,16]
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