Influence of three stage ultrasound—intermittent microwave—hot air drying of carrot on physical properties and energy consumption

Abstract

Innovative drying technologies are frequently introduced to minimize various disadvantages of hot air dryers such as high energy consumption and low quality dried products. The aim of this study was to investigate the influence of ultrasound (40 kHz for 10, 20, and 30 min) and intermittent microwave (360, 600 and 900 W at pulse ratios of 1, 2, 3 and 4) on physical properties of carrot during low temperature hot air drying at 40˚C. Drying time decreased during continuous microwave drying (pulse ratio of 1) due to higher internal temperature and water vapor pressure of the samples. The lowest bulk density was observed when ultrasound was applied for 30 min at 900 W microwave power with pulse ratio of 1. This result was attributed to a higher number of micro-channels created in the samples, which led to generate a higher porosity. Shrinkage of the samples decreased by increasing microwave power due to a shorter application time of microwave at higher powers. By extending ultrasound application time, rehydration increased by 17.8% as a result of enhanced cell permeability and higher capacity for water absorption. In addition, specific energy consumption decreased by 38.1% by increasing microwave power owing to lower drying time. Overall, the combined drying method improved physical properties of dried carrots and decreased energy consumption, suggesting a suitable alternative for industrial applications.