Recent developments in radio frequency drying for food and agricultural products using a multi-stage strategy: a review.

Radio frequency (RF) drying is an emerging technology for food and agricultural products, holding features of rapid, uniform, stable, and volumetric heating, high energy efficiency, and moisture leveling. However, the RF drying with a single stage commonly has drawbacks of unexpected product quality, non-uniform moisture distribution, and prolonged drying time. The multi-stage drying approach could overcome the shortcomings of one-stage strategy accordingly by applying different drying methods or operating parameter values in each phase separately. This review describes the principle of RF heating, presents the typical systems and superiorities of RF drying, and provides a comprehensive overview on recent development in applications of both the one-stage and the multi-stage RF drying, and analysis of drying characteristics and merits for different types of the two-stage strategy. This review finally proposes recommendations for future studies in improving and optimizing the existing RF drying protocols and scaling up them to industrial applications.