Drying Kinetics of Pretreated Drumstick (Moringa oleifera) Leaves During Lyophillization

Studies were carried out to investigate the drying kinetics of Moringa oleifera leaves with or without pretreatments in a lyophilizer (freeze dryer) using established drying mathematical models. Nine thin layer drying kinetic models were fitted to experimental data. The performance of the models was evaluated by comparing coefficient of determination (R2) and reduced chi-square (χ2) values between the observed and predicted moisture ratios. The statistical software tool was used to perform regression analysis in order to evaluate the model constants. The constants of the models were evaluated using a nonlinear regression analysis with help of statistical software. In non-linear regression, the R2 and the reduced χ2 were employed to assess the goodness of fit of the mathematical models to the experimental data. The best fit to drying curves was judged to be the model having the highest R2 and the lowest reduced χ2 values. For explaining the drying kinetics of drumstick leaves, the Midilli-Kucuk model performed best, followed by the logarithmic model. The R2, reduced χ2, and root mean square error (RMSE) values of lyophilized Moringa leaves varied from 0.996 to 0.999, 0.0001 to 0.003, and 0.008 to 0.053, respectively. Fick’s diffusion model was applied to characterize moisture transfer from drumstick leaves, and effective moisture diffusivity was worked out. The values of Deff varied from 1.05*10−9–7.36*10−10 m2s−1 and 1.29 × 10−9–9.82 × 10−10 m2s−1 for pretreated and unblanched leaves, respectively, throughout the drying process. Activation energy for pretreated and unblanched lyophilized drumstick leaves ranged from 12.952 to 13.006 kJ/mol, respectively.