Foam-mat drying is an economical method compared to other drying methods commonly used today, especially convenient for products with high viscosity and difficult to dry in food powder production. In this study, the red-flesh dragon fruit foam drying study was arranged according to the Box-Behnken design with 18 treatments and 6 center point replications. The input variables were egg albumin (EA) at varying concentrations of 5, 10 and 15%, and glycerol monostearate (GMS) at varying concentrations of 1, 3 and 5%. The drying process is arranged at temperatures of 50, 60 and 70^oC. The dependent variables included in this study were betacyanin content (mg/100 g) and drying rate (g water/g dry matter/min). Response surface methodology was used to optimize the drying rate (g water/g dry matter/min) and betacyanin content (mg/100 g). Accordingly, the optimal conditions were found with concentrations of EA, GMS used and drying temperature of 10.43%, 2.97% and 63.21^oC respectively. These conditions created foam-dried red flesh dragon fruit powder containing optimal content of betacyanin is 54.33 mg/100 g at the optimal drying rate of 1.78 g water/g dry matter/min. Foam-mat dried red dragon fruit powder has beautiful color, low moisture content (8%) with the water solubility index (41.05%), water absorption index (3.5%) and hygroscopicity (20.11%) were determined.

Keywords: Red dragon fruit, Foaming agents, Foam mat drying, Betacyanin, Drying rate