Interfacial properties of Quillaja saponins and its use for micellisation of lutein esters

• Saponins show good functionality with respect to micellisation of lutein esters.
• Composition of aqueous phase affects the colour of un-/loaded micellar solutions.
• Loaded saponin micelles may form branched networks.
• High colour stability of LMS in the absence of light below pH 7.

Natural food colourants, colouring foods and bioactive food ingredients need to be solubilised for their incorporation in food. Aim of the present study was to investigate the micelle-forming properties of saponins from Quillaja saponaria Mollina (QS) in order to solubilise a lutein ester extract for its incorporation in food matrices. QS showed a high surface activity and functionality with respect to micellisation as derived from interfacial tension measurements and subsequent data fitting to the classical Frumkin model. The composition of the aqueous phase affected the lutein ester incorporation as revealed by particle size, zeta potential and colour measurements. In terms of morphology of lutein ester loaded saponin micelles (LMS), cryo-TEM micrographs showed depending on the composition of the medium both, spherical and elongated branched micelles.