Electrohydrodynamic drying of pennyroyal (Mentha pulegium): Kinetics, energy, exergy, quality attributes, and bioactive compound stability

Abstract
Preserving the medicinal value of plants such as pennyroyal (Mentha pulegium) during drying faces a fundamental challenge: conventional thermal methods inevitably degrade a considerable proportion of the very volatile and heat-sensitive compounds that constitute the plant's beneficial properties. Motivated by this limitation, the present study investigated electrohydrodynamic (EHD) drying, a non-thermal and energy-saving technique. To this end, the effects of two operational parameters—applied voltage (14, 17, and 20 kV) and electrode gap (2, 3, and 4 cm)—were evaluated on drying rate, specific energy consumption (SEC), exergy efficiency, physical quality attributes, and bioactive compounds. The experimental results clearly demonstrated that increasing the voltage while simultaneously reducing the electrode gap accelerated the moisture removal rate and shortened the overall processing time. The effective moisture diffusivity (Deff) ranged from 2.21×10–10 to 4.31×10–10 m2/s, with higher voltages improving this coefficient by 11.5% to 22.3%. The lowest SEC and the highest exergy efficiency were recorded at 20 kV and 2 cm electrode spacing. Raising the voltage from 14 to 20 kV at the 2- cm gap reduced SEC by 9.9% to 22.7%, while exergy efficiency increased from 17.52% to 32.21%. The intensified corona discharge and the resulting ionic wind enhanced the disruption of the boundary layer surrounding the leaves, thereby facilitating moisture transfer from the specimens. A moderate electric field intensity provided the greatest protection for photosynthetic pigments (total chlorophylls and carotenoids, following a consistent trend), whereas the largest electrode gap (4 cm) was most effective at preserving Total Phenolic Content (TPC), Total Flavonoid Content (TFC), and Antioxidant Activity (AA). This divergence highlights that phenolic and flavonoid compounds are considerably more susceptible to oxidative and chemical degradation than pigments. Furthermore, a multi-criteria optimization using the TOPSIS method, incorporating 11 performance indicators under three weighting scenarios, identified the treatment at 20 kV and 3 cm electrode gap as the preferred condition for the balanced scenario (Cᵢ = 0.593), while 20 kV and 2 cm (Cᵢ = 0.803) is recommended when energy savings are prioritised, and 17 kV and 4 cm (Cᵢ = 0.716) is superior for quality-oriented applications. These findings provide a practical decision-support framework for selecting EHD operating parameters based on specific application priorities.

Author
Mohammad Kaveh

DOI
https://doi.org/10.1016/j.afres.2026.102550

ISSN
2772-5022

Publish Date: 2026-08-27