## 3 Bioactive Compounds in Wine By-Products
### Extraction Methods of Bioactive Compounds
#### 3.1.2 Emerging Extraction Methods
Ohmic heating (OH): This is based on alternating current used for internal heat generation [93]. Moreover, this technique is associated with less aggressive heat treatments than conventional methods, as it can heat materials uniformly and rapidly, avoiding the denaturation of thermosensitive substances, including phenolic compounds [108; 109]. For example, [PERSON] et al. [110] applied OH pre-treatment (50 \({}^{\circ}\)C and 400 or 800 V.cm\({}^{-1}\)) to extract polyphenols from red grape pomace and found that under the same extraction conditions (30% ethanol at 50 \({}^{\circ}\)C for 60 min), the polyphenols yield increased from 440 to 620 mg GAE.100 g\({}^{-1}\) DW with the pre-treatment. Pulsed electric fields (PEFE): Electric fields are applied to a material placed between two electrodes. The pulse amplitude ranges from 100-300 V.cm\({}^{-1}\) to 20-80 kV.cm\({}^{-1}\)[111]. Typically, PEFE is performed at ambient temperature or slightly higher than the ambient temperature for a treatment time less than 1 s (ms or \(\upmu\)s) [112; 113]. The exposure of plant cells to a specific electric field can result in damage to the cell membranes, causing temporary (reversible) or permanent (irreversible) pore formation. This process is referred to as 'electroporation'. PEFE was used to study the extraction efficiency of polyphenols from two grape varieties (white--Muscat Ottonel and red--Pinot Noir). The authors showed that the application of PEFE significantly increased the content of the total polyphenols and flavonoids and the antioxidant capacity. In addition, PEFE in combination with a homogenization step leads to a significant increase in bioactive compounds and antioxidant capacity compared to PEFE-treated samples of crushed grapes [114]. Supercritical fluid extraction (SFE): This method uses the solvation of the compounds of interest in a solvent maintained above its critical pressure and temperature. The solvent is immediately recovered when the system returns to atmospheric conditions. One of the most commonly used supercritical fluids is CO\({}_{2}\). It is a green solvent that is cheap, environmentally friendly, easy-to-reach critical point (31 \({}^{\circ}\)C and 7.4 MPa), non-flammable, non-toxic, and non-carcinogenic [115]. The advantages of this method are a short extraction time, a low amount of solvent required, that it is environmentally friendly, and provides rapid solvent recovery. The main disadvantages are related to the high cost of the equipment and operation and complex optimization [116; 117; 118]. Pressurized hot water extraction (PHWE): This is a non-conventional method based on the extraction of molecules using hot liquid water as a solvent. To use this method, one must have both high temperature and pressure, exceeding 100 \({}^{\circ}\)C and 0.1 MPa, respectively (which is the boiling point of water at atmospheric pressure), but remaining below the critical point values (374 \({}^{\circ}\)C, 22.1 MPa). If water is used as a solvent, the PHWE method can be referred to by several names, including subcritical water extraction, superheated liquid extraction, pressurized liquid extraction, or accelerated solvent extraction [34; 119]. [PERSON] et al. [120] compared two extraction processes for the recovery of antioxidants from grape pomace. They compared PHWE (mixture of 50% ethanol-water, 9 MPa, 120 \({}^{\circ}\)C for 90 min) and supercritical CO\({}_{2}\) extraction (55 \({}^{\circ}\)C, 10 MPa, and 20% ethanol). It was found that the total yield and the yield of anthocyanins and phenolic compounds extracted were higher when the pressurized ethanolic solution was used. This process was more efficient in terms of the phenolic concentration and antioxidant activity. [PERSON] et al. [121] optimized the temperature of the extraction process of carbohydrates and phenolic compounds of grape pomace with PHWE.