## 4 Extraction Methods for Coriander Bioactive Compounds
### Non-Conventional Extraction Methods
#### 4.2.1 Microwave-Assisted Extraction  
Because it has a higher extraction efficiency than other conventional extraction techniques, microwave-assisted extraction, or MAE (Figure 2), is a relatively novel technique that is being utilized extensively to extract active components from a variety of plant materials [116]. MAE turned out to be far more efficient and cost-effective. Similar to classical solvent extraction, MAE involves the target compounds migrating out of the matrix through the solvent as the solvent diffuses into the sample matrix and removes the components via solubilization [116]. By combining an extraction method with microwave heating, MAE is a potential technology for the extraction of bioactive chemicals from vegetal material. The basis for microwave heating is the way that ionic conduction and dipole rotation cause the microwaves to interact with the molecules of the substance [117]. In addition to producing heat quickly, the MAE system can help solvents enter raw plant material and intracellular material to enhance ingredient transfer, shorten extraction times, and increase extraction rates [9]. The liquid-to-solid ratio, extraction power, extraction time, and type of extraction solvent all affect MAE efficiency [118]. MAE has been shown to be highly effective for the hydrodistillation of EO, and it is being studied on a number of fronts, including the polyphenols extraction [19]. This extraction method was applied by [PERSON], [PERSON] [119], in their investigation into the process of extracting polyphenols from coriander seeds, they aimed to maximize both the yields of total phenolic (TP) and total flavonoid (TF) compounds while also maximizing the antioxidant activity, as assessed through 1,1-diphenyl-2-picrylhydrazyl and reducing power tests. A Box-Behnken experimental design applying response surface methodology (RSM) was employed for the optimization of three parameters influencing MAE, namely, ethanol concentration (50-90% \(w/w\)), extraction time (15-35 min), and irradiation power (400-800 W). The best MAE conditions for concurrently maximizing polyphenol output and increasing antioxidant activity were determined by this study to be a 19 min extraction period with 63% ethanol and 570 W of irradiation power. Hence, under these optimal MAE conditions, the predicted values were in the order of 311.23 mg gallic acid equivalent/100 g dry weight (DW) for TP, 213.66 mg catechin equivalent/100 g DW for TF, 0.0315 mg/mL, and 0.1311 mg/mL for IC\({}_{50}\) and EC\({}_{50}\), respectively. A recent investigation by [PERSON], [PERSON] [120], consisting of a comparative study between MAE and conventional extraction (CE), used a hot maceration method, based on the yield of TPC and their profile, as well as the antioxidant activity of coriander leaves powder. During this study, a central composite design with RSM was applied for the optimization of four parameters influencing MAE, namely, ethanol concentration (%, \(V/V\)), microwave power (W), irradiation time (min), and solvent-to-solid ratio (mL/g), while CE was conducted using the classic water bath method. The study found that under the optimal conditions (50% ethanol concentration, 400 W microwave power, 2.14 min of extraction time, and a 75 mL/g liquid-solid ratio), TPC yield recovery was 37.94 mg (MAE) as opposed to 44.47 mg GAE/g DW (CE). The two extracts have a similar phenolic composition, according to the ultra-high-performance liquid chromatography (UHPLC) analysis. Moreover, no significant difference was recorded in terms of the antioxidant activity of both extracts. Therefore, these authors pointed out that there are many valuable advantages to using MAE as the processing time is short and the antioxidant activity and phenolic composition have not been affected by the extraction process.