Effects of vegetable porosity following microwave drying on absorption of dried vegetables

Abstract

The effects of porosity on the water absorption characteristics of dried vegetables were investigated. Water absorption characteristics of two kinds of vegetables (radish and eggplant) following microwave drying and hot air drying were measured at four temperatures ranging from 20 to 70°C. An infinite plane sheet diffusion model could be used to describe the water absorption process for these samples; a non-linear least squares method was applied to the diffusion model, and two parameters, saturated moisture content (Ms) and coefficient of water absorption rate (k), were obtained. The measured results agreed well with the calculated results. The saturated moisture content of microwave-dried eggplant was the highest of all the tested samples, meaning it had the highest moisture-retaining ability. In addition, changes in volume during soaking were determined by measuring the apparent density and true density of the dried vegetables at various moisture contents. Internal porosity was determined from apparent and true density, and the effects of porosity on the water absorption characteristics of dried vegetables were evaluated. Microwave drying was found to improve water retention in dried eggplant.