## 3 Bioactive Compounds in Wine By-Products
### Extraction Methods of Bioactive Compounds
#### 3.1.2 Emerging Extraction Methods
The experiment, which led to a higher concentration of the phenolic compounds (2.6 g.100 g\({}^{-1}\) of grape pomace) and a more significant carbohydrate recovery (85%), was carried out at 210 \({}^{\circ}\)C and 10 MPa. Ultrasound (UAE): An ultrasound can be utilized to enhance heat and mass transfer in plants by breaking down their cell walls through the cavitation effect [122]. UAE promotes greater solvent penetration into the cell material and shorter processing and residence times, resulting in better extraction yields and reproducibility. It also minimizes the use of solvents and emulsifier consumption, provides high extraction throughput, extraction of heat-labile components, significant savings in maintenance, lower energy requirements for extraction,and promotes a more eco-friendly and cost-effective processing method [111; 122; 123]. UAE can be easily combined with existing equipment as part of the technological plant or, if necessary, set up as a new production line [34; 124]. This extractive method was used by some authors in recent studies to recover phenolic compounds from winery residues [125; 126; 127]. [PERSON] et al. [128] appointed [PERSON] et al. [95] to use the UAE method to determine the total phenolic compounds that constitute different wine by-products from the Alentejo and Ribatejo regions. They found that the concentration ranged between 0.16 and 1.93 mmol GAE.g\({}^{-1}\) of the extract. [PERSON] et al. [96] extracted phenolic compounds and antioxidants from grape pomace and compared the efficiency of UAE with a conventional method (water was used as an extraction solvent with mechanical stirring). It was found that the properties of the extracts obtained with both methods were similar. However, at 50 \({}^{\circ}\)C, the UAE method was 8 times faster than the method with mechanical stirring (200 rpm). To increase the extraction yields, in the study developed by [PERSON] and [PERSON] [129], enzymatic pre-treatment of the residue was carried out, followed by UAE in combination with MAE. Natural deep eutectic solvents (NADES): These can be created by blending a hydrogen bond acceptor component (quaternary ammonium salts, such as choline chloride), natural hydrogen bond donors (such as sugars, alcohols, and amines), and up to 50% (\(v/v\)) water; it is possible to customize their physicochemical properties [91; 92]. The advantages of using these solvents are the versatility of their physicochemical properties, the relatively easy precess [92], and a wide range of polarity and high solubilization strength. Thus, they can be used as an alternative greener solvent [91; 92; 130]. However, there are also some disadvantages, namely, a high viscosity and very low vapor pressure. The latter parameter makes it difficult to evaporate the solvent to isolate the target compound, commonly performed by distillation. However, anti-solvents can be added, and liquid-liquid or solid-liquid extraction can be performed [92]. Bioactive compounds can be extracted and preserved with the use of NADES, making them suitable for various applications in the food, pharmaceutical, and cosmetic industries [87]. Recent studies have proven the success of using NADES for the extraction of polyphenols from wine by-products [87; 91; 92; 130; 131; 132]. The use of NADES containing choline chloride, tartaric acid, and water led to a 112% increase in the extraction efficiency of anthocyanins from grape pomace, when compared to the extraction efficiency achieved with acidified ethanol under the same conditions [87]. All the emergent extraction methods listed above can enhance the efficiency of extracting polyphenols, flavonoids, sugars, minerals, and carotenoids from plant materials and by-products [34]. These methods are crucial for the food industry, among others. They aid in product innovation, leading to a wider range of food industry products and more efficient processes, making the industry more competitive [133; 134].