# Advanced and Potential Methods for Extraction of Bioactive Compounds from Avocado Peel--A Review
## 4 Advanced Methods for Extraction of Bioactive Compounds from Avocado Peel
### Supercritical Fluid Extraction (SFE)  
Supercritical fluid extraction (SFE) is also considered an environmentally friendly process. This is an efficient technique for extracting thermolabile compounds from a solid or liquid matrix, using supercritical CO\({}_{2}\) (SC-CO\({}_{2}\)) as an extraction solvent. SFE obtained the most significant number of patents filed (7550 patents) for extracting compounds. Furthermore, SFE can operate at low temperatures without oxygen or light, which is critical for maintaining the purity and integrity of the extract prior to analysis. SFE has been used to extract alkaloids, phenolic chemicals, anthocyanins, flavonoids, carotenoids, saponins, and oils [34; 35]. It may be applicable to the avocado peel as well.  
Carbon dioxide is primarily capable of extracting non-polar molecules due to its polarity. To circumvent this problem, another solvent could be used in conjunction with CO\({}_{2}\) at deficient concentrations to improve the polarity of the supercritical fluid. Cosolvents have included ethanol or methanol and, more recently, ethyl lactate, vegetable oils, and ethyl acetate combined with less than 10% total CO\({}_{2}\)[35]. Using supercritical CO\({}_{2}\) has several advantages over traditional approaches. SC increased CO\({}_{2}\)'s diffusion coefficient and reduced viscosity, allowing it to quickly penetrate the pores of complex matrices, increasing extraction efficiency. Furthermore, because the depressurization process quickly separates CO\({}_{2}\), the extracts obtained via SFE are highly concentrated, leaving no trace of harmful organic solvents in the final product. Also, since CO\({}_{2}\) gas may be recycled, the disruption of cells by a quick depressurization treatment can be performed in the SFE equipment, which optimizes extraction by lowering the time and labor requirements [36]. Hitherto, PLE was compared to SFE to extract phytoactive compounds in buckwheat in a single case. The two types of extraction gave very similar results [36]. In the study of [PERSON] et al. [37], SFE was used to retrieve bioactive compounds from avocado peels and seeds. Before extraction, the dried avocado peels and seeds are milled to a particle size of 0.4 mm. Then, the SFE was performed using CO\({}_{2}\) as a supercritical solvent with operating conditions of 80 \({}^{\circ}\)C and 250 bar for 30 min. Ethanol was presented as a co-solvent in a ratio of 1:1.5 S:L.  
Thus, SFE is an alternative method for extracting valuable analytes from various matrices [38]. SFE is a selective and environmentally friendly technology primarily employed in large-scale industrial applications. However, it has also been examined as an unusual sample preparation technique because it decreases the usage of organic solvents while increasing yield [39; 40]. Although various solvents can be used as supercritical fluids for extraction, carbon dioxide is the most popular due to its numerous advantages [41]. It is GRAS (Generally Recognized as Safe) for use in the food industry, inexpensive, and readily available; it enables the reuse of CO\({}_{2}\) generated in other industrial processes, thus meeting some Green Chemistry principles. Its characteristics are essential because it enables the extraction of a solvent-free extract following depressurization, which is especially useful when the extract contains chemicals that are prone to degradation [34]. Carbon dioxide is widely known as an eco-friendly solvent, and several comprehensive reports have shown its benefits as a green solvent [41, 42]. From the point of view of environmental analysis, CO2 is the second green solvent, followed by water [43].