Salt-assisted ultrasonic pretreatment-microwave extraction for efficient recovery and GC-MS profiling of essential oil from Citrus grandis 'Tomentosa'.

An integrated salt-assisted ultrasonic pretreatment-microwave extraction method (SA-UPME) was developed for the recovery and GC-MS profiling of essential oil from Citrus grandis 'Tomentosa' (CGTEO) without organic extraction solvents. The extraction behavior was described using a first-order kinetic model, and the main operating variables were screened by Plackett-Burman design and optimized by Box-Behnken response surface methodology. Under the validated conditions of 185 W ultrasonic power, 11 min ultrasonic pretreatment, and 20 min microwave extraction, the CGTEO yield reached 17.36 ± 0.36 mg/g, which was approximately 32% higher than that obtained by conventional hydrodistillation (HD, 13.16 ± 0.34 mg/g). GC-MS peak-area normalization showed different relative volatile profiles for the oils obtained by the two methods. Monoterpene hydrocarbons were the predominant chemical class in both oils and accounted for 76.54% of the total peak area in SA-UPME-derived CGTEO compared with 62.33% in HD-derived CGTEO. The relative peak areas of d-limonene, γ-terpinene, β-myrcene, and α-pinene were higher in SA-UPME-derived CGTEO. FTIR spectra showed comparable positions of the major absorption bands in the two oils. Compared with HD, SA-UPME shortened the total processing time from 180 to 31 min and reduced the estimated electricity consumption from 1.50 to 0.17 kWh. Within the defined Path2Green assessment boundary, the overall score was 0.115 for SA-UPME and -0.079 for HD. SA-UPME-derived CGTEO also showed stronger antifungal activity than HD-derived CGTEO against the five tested Aspergillus species. Overall, SA-UPME provides an efficient laboratory-scale extraction approach for CGTEO recovery and chromatographic characterization under the evaluated laboratory conditions.