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Osmotic pretreatment is an effective way of reducing water from the biological products as well as simultaneously accelerating the drying kinetics. This research investigates the effect of osmotic pretreatment on the biological products in a vortex tube atmospheric freeze-drying (AFD) system. To facilitate the atmospheric freeze-drying in a laboratory scale, a vortex tube was connected to the compressor. A multi-mode heat input concept was tested successfully to study the drying kinetics without damaging the products. The products were compared with the samples that did not undergo the osmotic pretreatment process. In addition, the comparison was also made with the parallel studies on conventional vacuum freeze-drying (VFD). Results showed that the osmotic treatment enhanced the drying kinetics for both AFD and VFD systems. PRACTICAL APPLICATIONSThis paper investigated on how the osmotic pretreatment influences the quality of the product in a novel atmospheric vortex tube-assisted atmospheric freeze-drying system, and compared with the parallel studies using conventional vacuum contact drying system. Osmotic treatment of biological products using concentrated sugar solution demonstrates enhanced osmotic dehydration as well as drying rate in this novel atmospheric freeze-drying technique. This information is aimed to help in selecting appropriate osmotic agent as well as suitable drying process at even industrial level for efficient drying specifically, for biological and heat sensitive products. In addition, this work focuses on quality analysis along i.e., drying behavior with the variation of process parameters e.g., drying time, temperature, and moisture content for subzero drying. This findings would be beneficial for critical analysis in osmotic dehydration process and would further serve as a guideline for optimum design.

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