Microencapsulation of bioactive bilberry anthocyanins by means of whey protein gels

Abstract

Microencapsulation is a promising possibility to stabilise anthocyanins in foods. However, the use of protein hydrogels as matrix materials for microcapsules has not yet been investigated. In this study we show that by means of the emulsion method thermally induced whey protein-based microcapsules which are applicable for the encapsulation of an anthocyanin-rich bilberry extract can be generated from whey protein solutions. The influence of manufacturing conditions, like stirrer speed and emulsifier addition, on the morphological properties of the microcapsules at pH 1.5 and pH 3 was assessed. In tensiometric measurements, the water-in-oil (w/o)-emulsifiers phosphatidylcholinedepleted lecithin (PCDL) and Span 80 significantly reduced the interfacial tension at the w/o-interface in the presence of the whey proteins in the water phase and were therefore applied for the production of microcapsules. When no emulsifier or the emulsifier Span 80 was used during the microencapsulation process, aggregated and coalesced microcapsules were obtained. This indicates a loss of the interfacial activity of Span 80 due to the conditions during microencapsulation. Only PCDL was effective in stabilising the emulsion droplets during gelation and the mean diameter of the generated microcapsules could be significantly decreased to 20–70μm. Finally, microcapsules containing up to 10% bilberry extract with a mean diameter below 50μm could be prepared by use of PCDL. For this, a microcapsule formed at pH 1.5 was favourable for the encapsulation of bilberry extract due to observed detrimental interactions between whey proteins and bilberry extract compounds at pH 3. The results of this study shall help to facilitate the development of innovative protein-based encapsulation systems using the emulsion method.