Impact of operating conditions on a single droplet and spray drying of hydroxypropylated pea starch: Process performance and final powder properties

Abstract

AbstractFor an efficient production of spray‐dried fine powders having controllable properties (size, size distribution, and morphology), finding suitable operating conditions and an appropriate initial composition of the fluid material is important. For this purpose, a suspension device is employed to investigate the drying kinetics of a single droplet of hydroxypropylated pea starch (HPS). In the current work, the effect of the drying air temperature (80–160°C) and of the initial solid content of the agent (15–30%w/w) on the drying kinetics, shrinkage, and locking point of a single droplet was systematically investigated to acquire the optimal conditions required for producing HPS powder using a pilot‐scale spray dryer. In addition to the previously mentioned parameters, the atomization pressure effect (2–3 bars) on the spray‐drying process yield, thermal efficiency, and final powder properties were also considered. A laboratory‐scale X‐ray microtomograph and a camsizer‐XT were employed for the acquisition of three‐dimensional images and surface morphology of single dried particles and spray‐dried powder, respectively. Hollow particles were obtained in all single droplet experiments. The drying kinetic study results were supported by those obtained by the spray drying of HPS. An increased temperature of the drying air and the initial solid content of the solution results in higher powder recovery, lower residual moisture content, and larger particle size. Otherwise, the final particles are larger at a decreased atomization pressure. The optimized parameters for the high spray‐drying process yield (24.54%; 3 bars, 140°C, 25 wt%) and better powder homogeneity (span = 2.31; 3 bars, 140°C, 20 wt%) were defined. A mixture of particle morphologies was observed among the different final powders. A broken shell corresponding to rigid particles was obtained at a drying temperature of 140°C and an initial solid content of 25 wt%. A nonbroken particle refers to a pliable particle that corresponds to inflated and collapsed particles dried at high and low drying temperatures.