Effect of Pulsed-Spouted Bed Microwave Freeze Drying on Quality of Apple Cuboids

The effects of novel Pulse-Spouted Bed Microwave Freeze Drying (PSMFD) technology on the quality on natural food products have been investigated. The objective of this research was to study effects of this novel technology on dielectric properties and quality characteristics (moisture content, porosity, microstructure, texture, color, and flavor) of apple cuboids as compared with the conventional drying technologies (air drying and freeze drying). During the first 45 min of drying, the dielectric properties increased due to partial conversion of water from ice to liquid, and then gradually decreased due to the moisture removal. Microwave energy increased sample temperature from minus 20 A degrees C to + 67 A degrees C, which resulted in fast drying to 0.09 g/g within 270 min. Porosity increased almost linearly, reaching 0.87 at equilibrium moisture content. Hardness of apple cuboids increased to 350-450 kPa due to the glass transition in the final period of drying. Better preservation of apple color and volatile compounds demonstrated the benefits of the hybrid PSMFD technology for the production of premium quality dried fruits compared to air drying and freeze drying.