## 5 Green Emerging Extraction Techniques
### Microwave-Assisted Hydrodistillation (MAHD)  
MAHD consists of the absorption of microwave electromagnetic energy by polar molecules inside the plant material through dipole rotation and ionic conductance. These processes increase the pressure inside the cells, leading to the disruption of membranes and the release of volatile bioactive compounds, which are subsequently recovered through a condensation system. MAHD ensures more rapid heating using the water inside the plant matrix without the need for additional water, allowing for energy and water savings [196]. Hence, MAHD has been developed to reduce energy and time in lab-scale reactors up to industrial-scale systems [186]. This technique shows reduced extraction times, requires less solvent, and allows for a higher recovery of EOs compared to traditional methods [46; 196]. Moreover, the biomass is treated more homogeneously than in classical distillation since the irradiation is not focused on the bottom of the reactor, as occurs in classical distillation [186]. [PERSON] et al. [186] investigated the volatile fraction (VF) of fresh, dried, and pelletized hops using MAHD followed by GC-MS for their characterization. The optimized lab-scale protocol yielded the best extraction value of 20.5 mLVF/kg of dry matrix for fresh hops. However, when the highest matrix amount was used (3 kg), the extraction yield was reduced to 17.3 mLVF/kg of dry matrix. Then, the authors test a pilot reactor able to process 30 kg of sample. In this case, the yields increased to quadruple and double the labscale yields in pelletized and dried products, respectively. [PERSON] et al. [187] recovered terpenoids from sage herbal dust through MAHD and compared them with conventional hydrodistillation. A total of 55 terpenoids were identified in the EOs of sage herbal dust via GC-MS analysis. The authors found that the chemical composition of the EOs differed significantly according to the method used. This could be explained by chemical alterations that occur during distillation, such as oxidation and hydrolysis. Despite this, the main compounds were present in all samples. Viridiflorol (21%), camphor (16.54-19.05%), and \(\alpha\)-tujione (11%) were the main compounds obtained via hydrodistillation. Moreover, ledene oxide-(II), cryophyll alcohol, o-cymen-5-ol, widrold, and longifolenaldehyde were only identified in the sample subjected to this method, where they represented 6% of the sample. In MAHD, at 90W, camphor (24.88%), \(\alpha\)-tujione (22.21%), and eucalypt (18.37%) were the main compounds; while at 360W, the main compounds were viridiflorol (33.27%) and verticiol (13.71%). In other MAHD samples, viridiflorol (17.17-23.7%) and camphor (14.46-18.82%) were the most predominant compounds. Aromadendrene oxide, phenylethyl alcohol, globulol, alloaromadendrene, and linalyl acetate made up 9.64% of the MAHD samples. [PERSON] et al. [190] applied both traditional and emerging extraction techniques to obtain peppermint extracts and EOs. Conventional hydrodistillation and MAHD were used for the recovery of EOs, which retrieved a high content in terpenoids, namely, menthol, menthone, isomenthol, eucalypt, and isomenthone (Table 5). Due to the high concentration of terpenoids in these samples, the EOs were revealed to reduce the power of cupric ions, the chelating of metals, and total antioxidant activity. Soxhlet extraction, SFE, microwave-assisted hydrodistillation, and UAE were applied for the non-selective recovery of peppermint lipophilic extracts. SFE extracts were useful for the green production of solvent-free peppermint extracts rich in terpenoids and other lipophilic bioactives. MAHD was identified as an alternative to traditional methods of recovering EOs.