Fig extract drying: The relationship between the main operating parameters of a pilot-scale spray dryer and product specifications

This study aims to optimize extraction and drying conditions of fig syrup. Drying was done in a pilot scale two-fluid nozzle spray dryer. A total of 27 experiments were conducted with varying inlet air temperatures, air flow rates, and also a maltodextrin (MD)- low methoxyl pectin (LMP) ratios. While feed rate, feed temperature, and compressed air flow rate of the atomizer were kept constant. The results of differential scanning calorimetry revealed that high levels of glucose and fructose in the extract resulted in a low glass transition temperature of fig syrup. By an increase in the inlet air temperature, the powder bulk density decreased. However, the MD:LMP ratio and the air flow rate were not significantly effective (p < 0/05) in changing the bulk density. SEM micrographs of spray-dried particles and particle size distribution analysis showed that particles were largely in a range of 5 to 50 μm. The best powders were obtained at an inlet air temperature of 170°C.