Optimization and modeling of mass transfer kinetics during foam-mat drying of date syrup

Foam-mat drying is one of the newest drying techniques, in which liquids or semi-liquids are transformed to stable foams and they were then exposed to hot air drying. In this study, the foam-mat drying technique was applied to produce date syrup powder, and the production process of the date syrup powder was optimized using response surface methodology. Independent factors were maltodextrin (0, 10, and 20% w/v) and albumin (5, 10, and 15% w/v), and the responses included foam stability, density, moisture content, water solubility index, water absorption index, bulk density, tapped density, pH, and rehydration ratio. The drying process was performed at three temperatures of 50, 60, and 70 ºC on 4- and 6-mm foam thickness to evaluate the drying behavior of the optimized date syrup foam, and 11 drying models were used to investigate the drying kinetics. According to the results of the present study, Page model was able to describe the drying behavior of date syrup foam at all drying temperatures and foam thicknesses. The effective moisture diffusivity was also calculated using Fick’s second law and it was in the range of 2.43 × 10-8 to 3.08 × 10-8 m2/s and 4.67 × 10-8 to 6.21 × 10-8 m2/s with activation energy values of 10.95 and 13.05 kJ/mole, respectively, for 4- and 6-mm foam thicknesses.