Colorant and antioxidant properties of red-purple pitahaya (Hylocereus sp.)

Abstract

Introduction. Red-purple pitahaya (Hylocereus sp.) is a promising crop grown commercially in dry regions of Central America. Both its skin and flesh are characterized by being a glowing, deeply red-purple color. Materials and methods. The main physicochemical characteristics of three commercial cultivars of red pitahaya were assessed, including total phenolic compounds contents, total betacyanins, vitamin C and oxygen radical absorbance capacity (ORAC). Thermal stability of betacyanins at different temperature and pH was also assessed. Results and discussion. Pitahaya fruit has a low vitamin C content ranging from (116 to 171) µg·g^–1 of fresh pulp without seeds, but it is rich in betacyanins [(0.32 to 0.41) mg·g^–1] and phenolic compounds [(5.6 to 6.8) µmol Eq gallic acid·g^–1]; it has a high antioxidant ORAC value of (8.8 to 11.3) µmol Eq Trolox·g^–1. Visible spectra of aqueous fruit extracts were very similar to that of pure betacyanin. Indeed, the characteristic color of juice diluted to 1% presents a high hue angle (H° = 350º ± 3) and high chroma values (C* = 79 ± 2). Thermal stability of pitahaya betacyanin decreases with pH, but it remains compatible with industrial utilization as a colorant (half-time = 22.6 min at 90 °C at pH = 5 of the fruit) and was found to be very similar to that previously reported for beetroot. Conclusions. Pitahaya juice combines the functional properties of a natural food colorant with high antioxidant potency.