## 5 Green Emerging Extraction Techniques
### Supercritical Fluid Extraction (SFE)  
SFE consists of the use of a dense gas or compressed liquid lacking any molecular interactions. The supercritical fluid exhibits properties of both gas (mass transfer, diffusion, lower viscosity, high penetration power) and liquid (high density, solvent power, reduced surface tension, and viscosity) at temperatures and pressures above critical points, with tunable density [181; 197]. SFE is a fast, efficient, economical, selective, and simple procedure for the extraction of terpenoids [198]. Carbon dioxide (CO\({}_{2}\)) and water are the two commonly used supercritical fluids in the industry on a large scale. However, the corrosive nature of water limits its use in the food and pharmaceutical industries [181; 198]. SFE with CO\({}_{2}\) as the solvent uses an essentially non-toxic solvent with low potential for the formation of interferents. Moreover, CO\({}_{2}\) has a low critical temperature and a high density, which makes it suitable for the extraction of heat-labile compounds and a high-dissolving power, respectively [181; 198]. Supercritical CO\({}_{2}\) extraction (SCO\({}_{2}\)) has a low polarity index, making it useful for dissolving lipophilic compounds such as Eos but unsuitable for polar compounds [181]. Therefore, the inclusion of polarity modifiers such as ethanol (EtOH), as well as the development of SFE apparatus capable of producing pressures over 600 bar, enables the extraction of several intermediate polarity compounds [45]. [PERSON] et al. [194] extracted valuable chemical compounds from dry leaves of _Piper klotzschianum_ by SCO\({}_{2}\). The sesquiterpenes were the most representative class in the extracts, in which the major constituents found were germacrene D, pipercallosidine, 14-oxy-\(\alpha\)-muvioleno, bicyclger-macrene, and (\(E\))-caryophyllene. The authors found that when using a co-solvent, the polarity increased, which resulted in an increased yield of some compounds due to a slight decrease in the percentage of hydrocarbons extracted. In another study, [PERSON] et al. [191] evaluated carotenoid recovery from 15 carotenoid-rich fruit and vegetable wastes. SFE allowed for the extraction of carotenoids from a mixed sample of fruit and vegetable matrices and provided high recovery levels, which ranged from 74% to 99% \(w/w\). The authors also found that the carotenoid extraction appeared to be influenced by the polysaccharide and moisture content of vegetable matrices. [PERSON] et al. (2015) developed a method for the extraction of oxygenated terpen from caraway using subcritical water extraction (SWE). Each terpenoid's chemical structure had a different effect in its extraction. For instance, the ideal conditions for carvone extraction were 170 \({}^{\circ}\)C and 15 min, while those for limonene were 110 \({}^{\circ}\)C and 10 min. SWE resulted in a higher carvone yield (28.5 mg/g caraway) than solvent extraction (20.2 mg/g caraway) and hydrodistillation (19.8 mg/g caraway). This study also showed that oxygenated terpen such as carvone had a high solubility in subcritical water, while non-oxygenated terpene like limonene could partially be converted to carvone through SWE.