Combining desiccant dehumidification with Hot Air and Microwave food drying: a sustainable and economical method to produce dried snacks

Abstract Solar hot air drying is a food dehydration method that is quickly gaining traction in South Asia due to its very low capital and operational cost. The long drying time and high temperature are the primary sinks of product quality in this process. The deterioration of cosmetic quality of food due to exposure to high temperatures over prolonged durations is an economical challenge as well since it results in a portion of dried product to be discarded. The objective of this work was to reduce the energy consumption and drying time, while obtaining a product quality competitive with energy extensive methods. To achieve this objective, a combined desiccant-convection-radiation dryer was designed and tested. A solar powered thermally regenerated desiccant dehumidifier was installed upstream of a Hot air – Microwave combined food dehydrator. The experimental results were compared with and without desiccant dehumidification. ‘Solanum tuberosum’ potato was cut into 3 mm thick slices and identical control samples of the potato slices were dehydrated using Hot air drying at 60 oC, Microwave drying at 1 kW Microwave power, Combined Hot air – Microwave drying, and Desiccant assisted Microwave – Convection drying. The drying time of the control sample with Desiccant assisted Hot air – Microwave drying was found to be the lowest, resulting in 81.7% reduction in drying time compared to Hot air Convection drying, 27.7% compared to MW drying and 13.3% compared to Microwave – Convection drying. The color retention was also found to be the highest for Desiccant assisted Microwave – Convection drying. The dried potato slices preserved 87.8% of their original color with this method, which is comparable to the results that are obtained with Freeze Drying.