Electrohydrodynamic, oven and natural drying of mint leaves and effects on the physiochemical indices of the leaves

Abstract

Electrohydrodynamics (EHD) enhanced the thin-layer drying of mint (Mentha Spicata Huds) leaves using multiple point-to-plate electrodes. Its configurations were carried out under DC high voltage and its effects were compared to oven drying at 40 °C and open-air-drying with natural convection at 25 °C. The EHD was run in an optimum electric field of 3.2 kV·cm-1 using positive ionising conical needles to a plate electrode covered by a steel screen grid to prevent the leaves drifting. The samples subjected to the EHD and oven exhibited faster drying kinetics than natural convection. Compared to the oven drying, the EHD electrical power consumption was negligible. The EHD method developed fewer undesirable changes in the colour features and the leaves' total chlorophyll, whereas the oven-dried sample colour underwent a significant change in colour. The samples dried by EHD had lower active microorganisms. The empirical modelling, based on the maximum value of R2 and the minimum value of RMSE and SSE between the experimental and predicted moisture ratios, showed that the diffusion and logarithmic models were the best models for describing the EHD and oven drying behaviour of the mint leaves.