Drying characteristics and drying quality of carrot using a two-stage microwave process

Little detailed information is available on the alternative of using varying microwave power during drying of food products. Experiments were made to study microwave drying characteristics and dried product quality. A two-stage microwave power system using a first and second stage power input for varying times during drying was used. The study focuses on describing microwave drying characteristics of carrot and discussing the effect of sample thickness, power applied during first-stage (first-stage power), power applied during the second-stage (second-stage power) and duration of first-stage on beta-carotene content, and rehydration ratio. The dehydration rate increased and the drying energy consumption decreased, as the thickness of the sample decreased, power level increased and mass load decreased. There were two falling rate periods when using microwave drying of carrot, the first falling rate period being over moisture contents of 1.0 (d.b.), and the second falling rate period applying at moisture contents less than 1.0 (d.b.). The same water loss will consume more energy and the energy curve was shown to the steeper when the moisture content is less than 1.0 (d.b.). Slice thickness, first-stage power, second-stage power, and duration of the first-stage affected beta-carotene content and rehydration ratio. The rehydration ratio of the dried products decreased with increase in duration of the first-stage and slice thickness. beta-carotene content decreased with increase of power applied during the second-stage and duration of the first-stage. With the exception of the effect of first-stage power on beta-carotene content and duration of the first-stage on the two quality indicators, slice thickness, first-stage power, and second-stage power significantly affected the two quality indicators. (c) 2004 Elsevier Ltd. All rights reserved.