Microwave dehydration of apple fruit: Investigation of drying efficiency and energy costs

The main incentive in processing fruits such as apple is reduction of losses and gaining added value. In this research, drying kinetics and drying efficiency of Golden Delicious apple slices are investigated using hot air flow and uniform microwave drying. Microwave power levels, 500, 1,000, 1,500, and 2,000 W, air temperatures, 40, 50, 60, and 70 degrees C and air velocities, 0.5, 1, 1.5, and 2 ms(-1) were selected. Results revealed that microwave dehydration is highly time-efficient with 80% reduction of processing time, compared to hot air method. Highest value of drying efficiency was found in microwave method and it was reduced by 99% in the case of hot air drying. Energy costs to cover the drying process were decreased by 60% when the microwave method was used. Technically speaking, microwave drying resolves insufficiency of hot air method along with a significant enhancement of drying rate, drying efficiency and energy economy. Practical applicationsDrying of agricultural commodities is known as a main challenge in the processing industry regarding the waste reduction, longer shelf time, easier transportation, and storage. The main technique in this regard is currently hot air convection method which suffers energy consumption and surface hardening. Reduction of drying time and energy consumption with simultaneous enhancement of drying efficiency and energy economy are well known features in modern drying technologies such as microwave method. However, microwave systems are rarely utilized in industry, because of lack of operating information and high-tech hardware issues. Application of microwave technology in dehydration of apple fruits can result in significant improvement in the processing economy. Volumetric and uniform heating as the primary benefit of microwave drying can be mentioned as an undeniable incentive to producers, processors and industrialists. Additionally, investigation of kinetics of drying is the first step for dryer design or scale-up.