Effect of blanching on microwave freeze drying of stem lettuce cubes in a circular conduit drying chamber

► Dielectric properties of stem lettuce due to different pretreatments were studied. ► Microwave blanching alters dielectric properties and microstructure of stem lettuce. ► Microwave blanching reduces drying time better compared to boiling water blanching. ► Microwave freeze drying can be divided into three periods based on corona discharge.