Abstract

The effect of microwave and blanch pretreatments on the drying kinetics and quality of white yam ( Dioscorea rotundata ) was investigated. Yam cubes destined for hot air drying at temperatures 70–90°C were predried in a domestic microwave or blanched in hot water for 1–5 min. Microwave pretreatment time had a positive significant effect on drying rate but both pretreatments had a negative influence on the ascorbic acid content and the nonenzymatic browning. The optimum drying conditions were a microwave pretreatment time of 5 min and a temperature of 70°C and a blanching time of 1 min at a temperature of 80°C. Among the models fitted, the Midilli et al. and the Page models gave the best fits for yam cubes predried with microwave and blanch, respectively. The effective moisture diffusivity for microwave‐assisted drying increased from 1.05 × 10⁻⁸ m² s⁻¹ to 2.00 × 10⁻⁸ m² s⁻¹ while the hot water blanched samples decreased from 1.53 × 10⁻⁸ to 8.81 × 10⁻⁹ m² s⁻¹ with time. The study demonstrates that microwave‐assisted drying could be used to enhance heat and mass transfer processes to produce better quality dried yam products.

Pretreatment to drying is essential to enhance the effectiveness of energy utilization in hot air dryers. In this study, the application of microwave as predrying step to hot air improved the energy efficiency and produced better quality dried yams. Therefore, predry microwaving for a shorter time interval to hot air drying should be considered by the food industry as an efficient drying method for white yam ( Dioscorea rotundata ) with respect to minimization of processing time, ascorbic acid degradation, brown pigment formation, and improvements in the quality and functionality of dried yams.