Effect of drying methods on the physical properties and microstructures of mango (Philippine 'Carabao' var.) powder

Mango powders were obtained at water content below 0.05 kg water/kg dry solids using Refractance Window (R) (RW) drying, freeze drying (FD), drum drying (DD), and spray drying (SD). The spray-dried powder was produced with the aid of maltodextrin (DE = 10). The chosen drying methods provided wide variations in residence time, from seconds (in SD) to over 30 h (in FD), and in product temperatures, from 20 degrees C (in FD) to 105 degrees C (in DD). The colors of RW-dried mango powder and reconstituted mango puree were comparable to the freeze-dried products, but were significantly different from drum-dried (darker), and spray-dried (lighter) counterparts. The bulk densities of drum and RW-dried mango powders were higher than freeze-dried and spray-dried powders. There were no significant differences (P <= 0.05) between RW and freeze-dried powders in terms of solubility and hygroscopicity. The glass transition temperature of RW-, freeze-, drum- and spray-dried mango powders were not significantly different (P <= 0.05). The dried powders exhibited amorphous structures as evidenced by the X-ray diffractograms. The microstructure of RW-dried mango powder was smooth and flaky with uniform thickness. Particles of freeze-dried mango powder were more porous compared to the other three products. Drum-dried material exhibited irregular morphology with sharp edges, while spray-dried mango powder had a spherical shape. The study concludes that RW drying can produce mango powder with quality comparable to that obtained via freeze drying, and better than the drum and spray-dried mango powders. (c) 2012 Elsevier Ltd. All rights reserved.