Automated vacuum drying kinetics, thermodynamics, and economic analysis of sage leaves

Vacuum drying of sage leaves is important for preserving their essential oils, flavor, and medicinal properties by reducing oxidation and thermal degradation, but previous research has not investigated its impact on drying speed, thermodynamic properties, mathematical modeling, or economic viability. This study employed an automatic vacuum dryer at temperatures of 40 °C, 50 °C, and 60 °C under different pressure conditions (atmospheric, -5 kPa, and − 10 kPa) with a 1 cm layer thickness. Results showed that increasing temperature and decreasing pressure significantly improved drying efficiency, reducing the process time to just 90 min while achieving a drying rate of 22.34 kg water/kg dry matter/h and an effective moisture diffusivity of 6.716 × 10⁻⁹ m²/s under optimal conditions (60 °C and − 10 kPa). The Page model was identified as the most suitable for describing the thin-layer drying behavior. Thermodynamic analysis revealed activation energy values between 19.4 and 37.7 kJ/mol, with activation enthalpy decreasing at higher temperatures and lower pressures. The negative activation entropy values indicated chemical adsorption or structural modifications during drying. From an economic perspective, the most efficient drying conditions reduced the payback period to less than two months, demonstrating strong commercial potential. These findings highlight the industrial promise of vacuum drying for herb processing, with future research opportunities in process optimization, application to other herbs, and sustainability assessments to further enhance efficiency and economic benefits.