Unusual drying behaviour of droplets containing organic and inorganic solutes in superheated steam

There are currently limited studies on the effect of superheated steam (SHS) on the solidification behaviour of droplets with dissolved solids which is a core phenomenon in spray drying. In this work, the single droplet drying technique was used to investigate how SHS affects the particle formation process of organic sugar droplets (lactose and mannitol), protein droplets (whey protein isolate) and droplets containing inorganic solute (sodium chloride). Unexpected droplet drying phenomenon was observed differing from drying behaviour typically assumed in the literature. While SHS is well known to result in slower drying rates below the inversion temperature, it also exhibits a lower potential to remove moisture at the end point ‘pseudo-equilibrium’ stage of drying. This led to lactose and mannitol droplets encountering incomplete moisture removal challenges in its drying process. The higher constant rate drying temperature experienced by droplet in SHS led to the precipitation of ultrafine protein particles. This higher constant rate drying temperature also led to the production of inverted pyramidal shaped salt crystals highlighting the potential of SHS as a useful medium for spray drying crystallization control.