Sequential microwave pretreatment enhances hydrodistillation of rosemary essential oil: Kinetic modeling, bioactivity and energy efficiency

The improvement of essential oil (EO) extraction using sequential processes remains underexplored compared to hybrid techniques. This study investigates a sequential approach combining microwave pretreatment with hydrodistillation (MWP-HD) for rosemary leaves focusing on extraction yield, kinetics, bioactivity, and energy efficiency. A central composite design was applied to optimize yield and extraction time as functions of pretreatment time, microwave power, and plant mass. Kinetic modeling, based on a multi- phase first-order model including simultaneous washing and diffusion, was used to quantify mass transfer mechanisms. Compared to hydrodistillation (HD), MWP-HD increased oil yield by 21.3% and reduced extraction time by 22.3% while energy consumption and CO2 emissions were nearly halved. The washing rate constant increased from 0.052 to 0.319, and the diffusion constant almost doubled. GC-MS/MS revealed a marked rise in p-cymene, which contributed to the improvement in antioxidant activity. Microscopic imaging confirmed structural disruption of leaf tissues after pretreatment. Antibacterial activity against Staphylococcus aureus, Bacillus subtilis, and Escherichia coli increased considerably, whereas antifungal effects varied, showing strong inhibition against most filamentous fungi. These findings demonstrate that sequential microwave pretreatment is a green and efficient strategy that enhances both process performance and oil bioactivity, offering a viable alternative for industrial-scale EO production.