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. 

In Vietnamese folk medicine, Bi ky nam (H. formicarum) tuber has been widely used to treat rheumatism, liver and intestinal diseases. This work aimed to study botanical, genetic characteristics and screening of the phytochemical constituents of wild H. formicarum of Phu Quoc Island, Vietnam. Anatomical characteristics of the plant material were described. Fresh leaves were used to analyze DNA barcodes based on rbcL region amplified by PCR. Sequences of DNA products were identified by Sanger method and BioEdit 7.0.5 software, then compared to the control rbcL sequences published in GenBank by BLAST. The tuber powder was studied for pharmacognostic parameters, preliminary phytochemical screening and total phenolic contents by Folin-Ciocalteu method. Results showed that the similarity between the rbcL sequences of H. formicarum leaves collected in Phu Quoc and the control one published in Genbank was 99%. Moisture content, total ash value and acid insoluble ash value of dried tuber powder were 11.06%, 9.60% and 0.70%, respectively. Raw material contained carotenoids, triterpenoids, flavonoids, phenolics, tannins, saponins, reducing substances and amino acids. Total phenolics content was about 58.847 mg pyrrogallol equivalent/g dried powder weight. Our results provided information about botanical, genetic and preliminary phytochemical characteristics of H. formicarum growing on Phu Quoc Island. This could be useful for the authentication of H. formicarum as a medicinal material.