Microwave hydrodiffusion-gravity as a cleaner extraction route for Abies holophylla needle oil: process greenness, monoterpene enrichment and value-added bioactivity

Abies holophylla oil extracted cleanly via microwave hydrodiffusion-gravity (MHG). • MHG maximized essential oil yield under optimized conditions (385 W, 35 min). • MHG reduced energy consumption and CO 2 emissions by 83.7% versus hydrodistillation. • Solvent-free MHG achieved the highest AGREEprep greenness score. • MHG supported biomass valorization through monoterpene enrichment. Forest conifer biomass is a promising renewable source of high-value volatile products, but its industrial utilization requires extraction routes that reduce process burden while preserving product quality. In this study, microwave hydrodiffusion-gravity (MHG) was developed as a cleaner production-oriented strategy for extracting essential oil (EO) from fresh Abies holophylla needles. The MHG process was optimized by face-centered central composite design and kinetic modeling, then benchmarked against microwave-assisted hydrodistillation (MHD), solvent-free microwave extraction (SFME), and conventional hydrodistillation (HD) in terms of extraction yield, energy and carbon performance, process greenness, volatile composition, and value-added bioactivity. Under the optimized conditions (385 W, 35 min), MHG produced the highest EO yield (16.55 ± 0.83 mL/kg DW). Compared with HD, MHD, and SFME, MHG technology reduces energy consumption and CO 2 emissions. Consistent with this, the AGREEprep analysis showed that MHG achieved the highest green score (0.62), reflecting its advantages in solvent-free operation, lower process load, reduced wastewater generation, and higher energy efficiency. GC-MS analysis further indicated that MHG favored enrichment of monoterpene hydrocarbons, particularly α-pinene and camphene. In parallel, the EO from MHG exhibited the strongest in vitro acetylcholinesterase (AChE) inhibitory activity among the reference extraction methods. Overall, the results demonstrate that MHG can simultaneously improve resource-use efficiency, reduce preparation burden, and enhance product functionality, providing a practical, cleaner extraction option for the high-value utilization of A. holophylla needles. Download: Download high-res image (282KB) Download: Download full-size image