## 3 Extraction of Vital Products
### Bioactive Compounds  
Industrial interest for naturally occurring bioactive compounds are on a continuous rise and to meet the growing demand, CE methods can be the viable option. Phenolic compounds are of particular interest, due to their antioxidant properties, which could be effectively extracted from  
Figure 1: Types of cavitation reactor (**a**) UAE (ultrasound-assisted extraction); (**b**) NPC (negative pressure cavitation); (**c**) HC (hydrodynamic cavitation, venturi) and overall mechanism. plants. Phenolic compounds are known to provide flavor, as well as distinct color to the wine. Phenolic compounds can be divided into three major groups, such as phenolic acids, flavonoids, and anthocyanins. Antioxidants present in plants, vegetables, and fruits can prevent cardiovascular diseases, cancer, premature aging and hence making them as one of the valuable ingredients of extraction. As antioxidants can prevent the cell oxidation process, there is a high demand in cosmetic, pharmaceutical and food industries. The extraction of natural antioxidants can replace the application of synthetic substances, such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA), because of their health concerns. Looking into the usefulness of bioactive compounds, their effective extraction is vital, but, the conventional extraction methods, such as maceration and Soxhlet extraction are inefficient. The root of _Salvia milliorrhiza_ contains bioactive phenolic compounds, such as salvianic acid B, which has shown better antioxidant activity compared to vitamin E. However, previous reports indicated the drawbacks of conventional reflux extraction method, due to its immediate hydrolysis to tanshinol and degradation at high temperature. But, the implementation of UAE was successful in obtaining the highest yield of salvianic acid B, which can be attributed to its low-temperature operation [8]. The recovery of resveratrol from functional foods (cookies and jams), via ultrasound assisted extraction has demonstrated the highest efficiency with an increase in the concentration of methanol compared to water, indicating its solvent dependent nature. Resveratrol is known for its antioxidant, anticancer and anti-aging activities. The yield increased significantly following a change in the concentration of methanol from 70 to 90% [9]. [PERSON] et al. [10] reported a 3-fold increase in phenolic compounds from grape pomace via UAE as compared to conventional mechanical agitation. UAE was implemented for the extraction of phenolic compounds from microorganisms, such as _Nannochloropsis spp_. Microalgae [11], which demonstrated two times better yield than maceration. The extraction of phenolic compounds and anthocyanins from rice bran (_Oryza sativa L._), indicated a significantly higher yield along with a noticeable reduction in the extraction time compared to conventional methods. HPLC analysis indicated \(\alpha\)-tocopherol, cyanandin-3-glucoside, sinapic acid, and vanillic acid to be predominant compounds in rice extracts [12]. Moreover, UAE enhanced the extraction of polyphenols from _Picea abies_ bark under optimized conditions, and seven polyphenic compounds (catechin, gallic, vanillic, syringic, p-cumaric, ferulic, and sinapic acids) were identified by HPLC analysis [13]. [PERSON] et al. [14] reported the extraction of antioxidants from pomergnanate peel using UAE and maceration methods. UAE exhibited an enhanced yield within less time compared to maceration under optimized conditions, where the continuous mode of extraction improved the yield by 24% while reducing the extraction time by 90%. [PERSON] et al. [15] also reported the extraction of antioxidants from _Zizyphus lotus_ fruit via UAE under optimum conditions. Phenolic compounds were extracted from defatted oat (_Avena sativa L._) bran via UAE, and the results showed a significant increase in the yield of free phenolics with a reduction in the extraction time as compared to conventional extraction.