Process intensification of clove (Syzygium aromaticum) essential oil recovery by homogenization-assisted salt-mediated low-water microwave distillation

HS-LWMD integrates homogenization, CaCl₂-mediated conditioning and microwave heating. • Low-water operation avoids bulk free-liquid heating during microwave distillation. • Active heating time fell 85.3% versus homogenization-assisted hydrodistillation. • Nominal active-heating energy fell 80.6% versus the hydrodistillation reference. • HS-LWMD retained a eugenol-rich relative GC–MS peak-area profile. A homogenization-assisted salt-mediated low-water microwave distillation (HS-LWMD) route was developed to intensify essential oil recovery from dried clove ( Syzygium aromaticum ) buds by coupling mechanical tissue disruption, salt-mediated moisture conditioning, and volumetric microwave heating. Single-factor experiments were used to screen homogenizer speed and time, salt type and concentration, soaking time, microwave power, and irradiation time; microwave power and time were subsequently optimized by central composite design. The CCD-predicted conditions were 0.34 mol L −1 CaCl₂, homogenization at 22,000 r/min for 5 min, salt-mediated soaking for 3 h, 594.4 W, and 26.4 min. The predicted oil yield was 87.99 mL kg −1 DW and the verified yield was 85.92 ± 0.65 mL kg −1 DW. Relative to homogenization-assisted hydrodistillation, the active heating stage decreased from 180 to 26.4 min, while the nominal active-heating energy, calculated from rated power and active heating time rather than measured electrical consumption, decreased from 4.86 to 0.942 MJ per batch. First-order kinetics described the microwave extraction curves slightly better than the second-order model. GC–MS showed that HS-LWMD oil retained a characteristic eugenol-rich relative GC–MS peak-area profile, with eugenol (59.93%), β-caryophyllene (24.10%), and eugenyl acetate (4.97%) as major constituents. The results demonstrate that integrating homogenization, salt-mediated pretreatment, drainage of excess liquid, and microwave activation can intensify the energy-demanding distillation stage while retaining the characteristic relative GC–MS peak-area profile of clove oil. Download: Download high-res image (118KB) Download: Download full-size image