. Solvent-Free Microwave Extraction
The modifications of standard extraction procedures, for example, hydro diffusion and solvent extraction are the sufferers of numerous evaporative components, weak coherence for isolation, and toxic residues of solvent at the stage of the end product. These problems encouraged the consideration of SFME (Solvent-Free Microwave Extraction) for a diverse appliance. This procedure is a prompt essential oils extraction from dry seeds, aromatic herbs and spices. Different benefits of this approach have been stated by researchers that can be summarized: to get essential oils with better selectivity and yield, shorter duration of extraction, and nature-friendly procedure [28].
SFME engages a combination of two methods which are heating of sample plant by the application of microwave technology tracked by dry distillation that works at atmospheric pressure without any solvent. Bayramoglu et al. used SFME technique to extract oregano at varying microwave power; 249W, 373W, 498W, and 622W, whereas the yields of extracted oils were determined based on each applied power of the microwave. The outcome revealed highest yields attained at 0.049, 0.052, 0.053, and 0.054, ml/g of oregano essential oil at 249W, 373W, 498W, and 622W power levels, respectively. Exemption with running at 249W (lowest microwave power), all remaining yields were observed to be higher (p < 0.05) [41]. Comparing to hydrodistillation, the extracted yield of essential oregano oil was 0.048 ml/g only, which is approximately 6% vaguely lower comparative to the highest yield of oregano oil obtained by SFME.
After that, Ferhat et al. gave a comparison of traditional approaches and SFME technique concerning antimicrobial activities, the residual content of solvent, effect of the procedure adopted towards the nature, yields, and period of extraction.
It was established that extraction by microwaving provides a shorter period for isolation of essential oil (30 min relative to 1 hour for cold pressing and 3 hours for hydro diffusion); yields (0.24%) from SFME is much improved than cold pressing and hydro diffusion (0.05% and 0.21% respectively); high utility of energy for doing cold pressing and hydro diffusion (applying mechanical motors) contrasted to rapid microwave extraction. No solvent and water used in this technique compare this technique as a cleaner character, with a more enormous antimicrobial potential of essential oils obtained by SFME procedure [42].