Effect of Blanching and Drying Temperatures on Physicochemical Properties of Red Dragon Fruit (Hylocereus polyrhizus) Peel Powder

Abstract

Large production of red dragon fruit by-products, which are frequently discarded from food industry has become a major waste problem. Converting this waste into useful products with good physicochemical properties could solve the pollution issues. Thus, a study was carried out to investigate the effect of blanching and drying temperatures on physicochemical properties of red dragon fruit peel powder. Dragon fruit peel was pre-treated with hot water at 90 °C for 2 minutes before being dried in hot air oven dryer at 50 °C, 60 °C and 70 °C. Results showed that the powdered sample of blanched and dried at 50 °C had significantly higher fiber, water activity and moisture content than those of unblanched/blanched and dried at 60 °C and 70 °C. Result also showed that the colour of this powder was similar to the fresh dragon fruit peel. When dried at 50 °C, the unblanched and blanched powders exhibited a slightly higher water solubility index compared to those dried at 60 °C and 70 °C. Based on the evaluation of bulk and tapped densities, all powders having the Carr Index in the range of values between 20 and 28 thus can be categorised as slightly poor flowing. For all conditions studied, powder that was blanched and dried at 50 °C was the best condition as it contained the highest amount of fiber with good physicochemical properties.