Antioxidant capacity of bilberry extract microencapsulated in whey protein hydrogels

Abstract

The application of antioxidative phenolic plant compounds, such as bilberry anthocyanins, as bioactive food additive may be facilitated by the protection through microencapsulation. The antioxidant capacity of the encapsulated compounds could thus be preserved until the point of action is reached. In this study, whey protein-based microcapsules loaded with an anthocyanin-rich bilberry extract were generated thermally after forming droplets by the emulsion method. The TEAC (Trolox equivalent antioxidant capacity)-assay was used to assess the antioxidant capacity of the anthocyanin-rich bilberry extract during all steps of the microencapsulation process. It could be shown that the loss of antioxidant capacity during microencapsulation can mainly be attributed to interactions between the whey proteins and bilberry extract compounds other than anthocyanins. An anthocyanin-attributed loss of antioxidant capacity occurred when an emulsifier was used in the microencapsulation process. In this case, a transition of hydrophilic anthocyanins to the oil phase was observed. Eventually, the generated bilberry-extract loaded microcapsules were investigated in terms of their release behaviour in digestive media. Due to the time-dependent diffusive release from the microcapsules, the degradation of anthocyanins at pH 6.8 was retarded in comparison to non-encapsulated bilberry-anthocyanins. However, anthocyanin degradation at pH 6.8 was minimal when the non-gelled bilberry extract–whey protein solution was incubated which indicates a protective effect of native whey proteins.The results of this study provide new insights regarding protein-based microencapsulation of phenolic compounds and are thus of relevance for the development of innovative encapsulation systems.