Colour studies on fruit juice blends from Opuntia and Hylocereus cacti and betalain-containing model solutions derived therefrom

The visual appearance and pigment stability of fruit juice blends from Opuntia and Hylocereus cacti and of betalain-containing model solutions derived therefrom were investigated at pH values ranging from 3 to 7. All samples were found to be stable as indicated by betalain contents as well as hue and chroma values over the complete pH range monitored. Both the juice and the purified betaxanthin solution from Opuntia ficus-indica cv. ‘Gialla’ were characterised by yellowish hues, while the juice and the purified betacyanin solution from Hylocereus polyrhizus displayed purplish tonalities. By blending the betaxanthin and betacyanin stock solutions, tailor-made hues covering the entire spectrum from bright yellow (h° = 84) to purplish-blue (h° = 333) were successfully produced. Since mixtures from purified betalains did not provide colour shades different from those obtained with raw cactus fruit juices, the use of the latter should be preferred both because of consumer-friendly labelling and improved pigment stability.