The Effect of Post-harvest Treatment on Antioxidant Properties of the White and Red Dragon Fruit

Introduction: Dragon fruits are widely used for their preventive and therapeutic effects against many chronic conditions due to the wide range of biological qualities associated with betalains and phenolic compounds. However, detailed reports on the antioxidant properties of various parts of the white and red dragon fruits and preferable post-harvest treatment modes are lacking and hence the current study. Objectives: To evaluate the antioxidant properties of air and oven-dried red and white dragon fruits grown in Meru, Kenya. Materials and Methods: Pre-developed thin layer chromatographic plates were sprayed with 1,1-Diphenyl-2-Picrylhydrazyl (DPPH) to evaluate the extracts of Hylocereus undatus and Hylocereus polyrhizus for their preliminary free radical scavenging activity. The extracts exhibiting the most promising antioxidant activity were subjected to additional investigation to determine their radical scavenging activity using spectroscopy. Results: 6 air-dried samples displayed possible antioxidant activity in the initial TLC technique, compared to four oven-dried samples. The ability of moderately polar extracts to scavenge free radicals was significantly lower (IC50=1.290-2.152) than that of polar extracts (IC50=0.497-0.768). The white-fleshed dragon fruit pulp and the red-fleshed dragon fruit skin were found to have higher radical scavenging activity (92.65±0.001 and 54.62±0.002, respectively). Conclusion: The antioxidant activity of the dragon fruit pulp does not appear to be impacted by oven drying at 40°C; however, the activity of the fruit skin and bracts is significantly reduced. The dragon fruit part, extraction solvent system and the drying conditions all impact the antioxidant activity.