## 4 Extraction Methods for Coriander Bioactive Compounds
### Non-Conventional Extraction Methods
#### 4.2.2 Ultrasound-Assisted Extraction  
One quick, easy, and inexpensive green extraction method that is gaining popularity is ultrasound-assisted extraction (UAE) (Figure 2). Its effectiveness has been proven in the extraction of bioactive chemicals, yielding greater recovery rates than traditional extraction methods while maintaining the extracts' intended properties [125]. Thanks to its high frequency ultrasonic waves, the UAE method has been used to extract several antioxidants from the plant matrix. Plant cell walls are broken, and the solvent is helped to infiltrate by the waves' contraction and expansion cycles and cavitation. Many variables, such as solvent concentration, solvent/material ratio, ultrasonication time, temperature, power, etc., affect the extraction rate and yield of UAE [126]. This extraction technique has been widely used for the extraction of bioactive constituents of coriander, namely, its polyphenols and EOs. During the study conducted by [PERSON], [PERSON] [127], after extracting EOs from coriander seeds via the SFE method, the resulting raffinate (also called pellet) was subjected to the extraction of phenolic compounds via UAE using 70% ethanol and water as solvents for comparative purposes. The results of their study showed that the content of dominant compounds in these extracts increased with the reduction of the mean particle size and was significantly higher in the 70% ethanolic extracts. Furthermore, a better antioxidant activity was attributed to these ethanolic extracts than to the aqueous extracts. Another study conducted later by [PERSON], [PERSON] [128] investigated the optimization of UAE of phenolic compounds from seeds using RSM, investigating the influence of three variables, namely, temperature (40-80 \({}^{\circ}\)C), extraction time (40-80 min), and ultrasonic power (96-216 W). The optimal conditions found are for TP (79. 60 \({}^{\circ}\)C, 49.20 min, 96.69 W), TF (79.40 \({}^{\circ}\)C, 43.60 min, 216.00 W), IC\({}_{50}\) (80.00 \({}^{\circ}\)C, 60.40 min, 216.00 W), and EC\({}_{50}\) (78.40 \({}^{\circ}\)C, 68.60 min, 214.80 W). The predicted values for TP, TF, IC\({}_{50}\), and EC\({}_{50}\) were 382.68 mg gallic acid equivalent/100 g, 216 mg catechin equivalents/100 g, 0.03764 mg/mL, and 0.1425 mg/mL, respectively. A more recent study conducted by [PERSON], [PERSON] [102] consists of a comparison of different conventional and non-conventional extraction techniques--maceration, Soxhlet, UAE, and rapid solid-liquid dynamic extraction--in terms of the extraction yield of polyphenols, antioxidant activity (FRAP, ABTS, and DPPH), and phenolic profile. The findings showed that the best polyphenol yield was attributed to UAE, while the best activities were attributed to rapid solid-liquid dynamic extraction (RSLDE). As for the phenolic profile, regardless of the extraction method, a total of ten compounds were identified, including eight phenolic acids and two flavonoids. The same study found that, except for luteolin and p-OH-benzoic acid, the RSLDE extracts had higher concentrations of gallic, p-OH-benzoic, and rosmarinic phenolic acids, as well as luteolin and apigenin. A longer extraction time was found to affect these concentrations positively. Nevertheless, the Soxhlet extracts exhibited greater amounts of chlorogenic, vanillic, and caffe acids, alongside the existence of syringe acid, which was not spotted in the RSLDE extracts when this process was applied for either 2 h or 6 h. The same authors, [PERSON], [PERSON] [102], characterized the volatile fraction obtained by the four methods mentioned above and highlighted the presence of 18 terpenoids in coriander seed extracts, all belonging to the monoterpene class, of which the most abundant compound was linalool. However, the volatile fractions of the coriander UAE and 6 h RSLDE extracts were primarily composed of acyclic monoterenes.