The red dragon fruit (Hylocereus polyrhizus), an available and popular agricultural source
in Vietnam, is potential material for food colourants because of the presence of
betacyanin. For the purpose of using dragon fruit extract to add colour to processed foods,
the study on the effects of extraction methods (conventional and ultrasound-assisted) on
the flesh and peel of the fruit was carried out using water as an extraction solvent. The
obtained results showed that using ultrasonic waves in extraction enhanced the total
betacyanin content in red dragon flesh and peel extract. Multiple regression analysis for
betacyanin and the independent variable was obtained with a high coefficient
determination (R2>0.8). The highest total betacyanin content predicted by the models were
27.49 mg/100 mL and 22.28 mg/100 mL corresponding to extracted at a ratio of 83.74%
red dragon flesh for 13.15 mins and the ratio of peel to the water of 90.63:9.37 for 12.91
mins. The obtained result could be applied to the food industry to use the achieved as a
natural food colour for further processing.