Colour evaluation of freeze-dried roselle extract as a natural food colorant in a model system of a drink

The roselle extract, using acidified water–95% ethanol (1:1) as a solvent, was subjected to freeze-drying. Maltodextrin and trehalose, 2 and 3 g/100 ml extract, were used as stabilisers. Addition of the stabiliser retarded anthocyanin degradation. Colour changes of the freeze-dried roselle powder during storage were monitored using the CIELAB system. It was found that pigment concentration markedly changed with a minor change in lightness and hue. However, the changes in chroma mainly came from anthocyanin degradation. The freeze-dried roselle powder with maltodextrin (3 g/100 ml) proved to have superior colour stability. A model system of a drink adding this powder was carried out and the colour evaluation was compared to drinks containing commercial colorants: SAN RED RC® and carmoesin. During a 12-week storage period at 30 °C, the change in hue of all three groups was within the same shade suggesting any change in pigment concentration had insignificant effect on hue shift. By contrast, the degradation of pigments highly correlated to changes in lightness and chroma. Even though a drink with roselle anthocyanin powder was the least stable in colour, the overall appearance of the drink was rated close to ‘like slightly’ throughout 56 days.