Drying characteristics and energy requirement of drying cowpea leaves and jute mallow vegetables

摘要

Thin layer drying of cowpea leaves (Vigna unguiculata) and jute mallow (Corchurus olitorious L) (African leafy vegetables) was studied at different temperatures (40oC -100oC) in a convective laboratory dryer. The study determined the drying characteristics of the vegetables, the maximum drying temperature and the drying energy requirements. Moisture content of the African leafy vegetables was determined on dry basis and the data were used to calculate moisture ratios and drying curves were plotted. The drying occurred in the falling rate period. The experimental data were fitted to fourteen thin layer drying models and the most appropriate drying model determined using correlation coefficient, mean square error and standard error of estimate. The model developed by Page showed good agreement with the data obtained from the experiments of this study because it consistently returned the required attributes from statistical analysis and its simplicity. The energy requirement of drying vegetables at the different temperatures was calculated. Cowpea leaves had a longer drying time of 304 min and a higher specific energy requirement of between 168 J/g at 100oC and 11.2 J/g at 40oC while jute mallow had a drying time of 256 min and an energy requirement of 155.3 J/g at 100oC and 10.6 J/g at 40oC respectively.