Study on preliminary screening of the triterpenoid constituents and in vitro tyrosinase inhibitory activity of dragon fruit flowers (Hylocereus undatus (Haw.) Britton & Rose)

Abstract

The flowers of Hylocereus undatus (Haw.) Britton & Rose have been reported in vitro antioxidant and tyrosinase inhibitory activities. This study screened preliminarily the triterpenoid constituents and evaluated in vitro tyrosinase inhibitory activity of H. undatus flowers. H. undatus flowers were harvested from Binh Thuan Province, Vietnam at four different flowering stages, and their five separated parts (stamen, pistil, petals, ovary, and sepals) were extracted with ethanol. Triterpenoids were identified in the extracts by thin-layer chromatography and Liebermann - Burchard reaction. Tyrosinase inhibitory activity was evaluated using the dopachrome method with L-tyrosine substrate and kojic acid as the positive control. Results showed that at the different flowering periods, there was the formation of different parts of the flowers. The triterpenoid compounds are the main constituents in the H. undatus flower extracts. The 70% ethanol extract from H. undatus flower at the stage of 2 - 3 days before blooming exhibited the strongest tyrosinase inhibitory activity with IC50 value of 266.4 μg/mL compared to that of 7.60 μg/mL of kojic acid. In the case of separation of flower parts, 70% ethanol extracts of each part inhibited weakly the tyrosinase enzyme. In conclusion, the present study provided information about the morphological characteristics of H. undatus flower collected from Binh Thuan Province, Vietnam. Triterpenoid was found as the main constituents of the ethanolic extracts of H. undatus flower. The 70% ethanol extract from whole H. undatus flower at the stage of 2 - 3 days before blooming exhibited strong tyrosinase inhibitory activity.