Study of Drying Uniformity in Pulsed Spouted Microwave–Vacuum Drying of Stem Lettuce Slices with Regard to Product Quality

Abstract

Drying uniformity, shrinkage, rehydration, and textural properties were measured to evaluate the quality of pulsed spouted microwave–vacuum-dried stem lettuce slices. Drying was carried out in a 5-cm (od) vacuum drying chamber at 7–10 kPa and microwave power level of 2.4 Wg⁻¹. Pulsed spouted microwave–vacuum-dried products were found to be more uniform compared to those obtained in a conventional rotating turntable microwave–vacuum dryer. The pulsed spouted mode also resulted in dried stem lettuce slices with low discoloration and high rehydration capacity as well as high hardness after rehydration. The total drying time required for pulsed spouted bed microwave–vacuum-dried products was approximately 60 min, reduced by 50% compared to conventional rotating turntable microwave–dried ones.