Microwave hydrodiffusion and gravity for rapid extraction of essential oil from Tunisian cumin (Cuminum cyminum L.) seeds: Optimization by response surface methodology

Recently, microwave hydrodiffusion and gravity (MHG) pushed the confines of the microwave assisted extraction (MAE) further toward an innovative, quick, efficient, and eco-friendly process for plant secondary metabolites extraction. The goal of this study was to optimize the microwave hydrodiffusion and gravity (MHG) process for the extraction of the essential oils (EO) from Tunisian cumin (Cuminum cyminum L.) seeds. The effects of different parameters: microwave irradiation time (8, 12, and 16 min), microwave irradiation power (150, 200, and 250 W), and moisture content (40, 50, and 60%), on the extraction yield were achieved using the response surface methodology (RSM) with central composite design (CCD). In order to elucidate the efficiency of the MHG, it was compared with conventional hydrodistillation (HD) in terms of kinetic, quantity and quality of obtained EO, environmental impact, and energy consumption. Results showed that, under the optimum conditions defined by the central composite face-centered (CCF) and calculated by the analysis of variance (ANOVA) (16 min of microwave irradiation time, 203.30 W of microwave irradiation power, and 44.67% of moisture content), the yield of cumin essential oil obtained with MHG was 1.579 +/- 0.05%. Meanwhile, compared with the HD process, the MHG successfully improved the EO yield (1.579 +/- 0.05% versus 1.550 +/- 0.07% with HD) in shorter extraction time (16 min versus 150 min with HD), less electrical consumption, lower carbon dioxide emissions (CO2), and smaller volume of waste water. Using the GC-FID and GC-MS analysis, the MHG provided more valuable EO with high amount of oxygenated compounds compared with the HD. Scanning electron micrograph (SEM) confirmed the efficiency of MHG for EO extraction. Thus, MHG appeared like rapid process, green technology, and desirable alternative protocol to enhance the quantity and the quality of the essential oil extracted from the medicinal and aromatic plants (MAPs).