Drying kinetics and quality of dried moringa leaves using different drying methods

Abstract

The drying kinetics and effect quality of dried moringa leaves using different drying methods. The methods were microwave (MW) alone, solar, sun, shade, hot air alone and blanch-assisted and MW-assisted hot air drying methods. The drying experiments were performed in the temperature range of 50 to 70 °C, MW-power of 270 to 720 W, blanching time of 1 to 3 min and sample thickness 3 to 20 mm. MW-pretreatment time, blanching time, sample thickness, microwave power and hot air temperature had significant effects on the drying time but they generally affected negatively the quality attributes (AA, TP, AOA, BI and FL) of the dried samples. Four thin layer drying models were fitted to the experimental data and the Midilli et al model most appropriately described the drying behavior of moringa leaves. Rehydration studies were carried out at the temperature of 60 oC and the hot air drying method best fitted Weibull equation, first order kinetic and exponential association equations. The optimal drying conditions of moringa leaves were found to be 50 oC at the thickness of 4.79 mm for hot air, and that for MWalone was 501.1 W at 3 mm thickness. For blanch-assisted hot air drying, optimal conditions were 70 oC and blanching time of 2.58 min while for MWassisted hot air drying, they were 70 °C at MW-power of 270 W and MW-time of 3 min. The results demonstrated that all the drying methods differentially affected the drying rates and the desirable and deleterious quality characteristics. The implications for the choice of drying method are discussed.