## 4 Extraction Methods
### Extraction in Supercritical Fluids
#### 4.1.4 Reactivity of Supercritical Solvents  
The ionic product of water (Kw) makes it a reactive solvent. Additionally, variations in temperature and pressure significantly affect the ionic product of water, influencing its reactivity. At 25 \({}^{\circ}\)C and 0.1 MPa, Kw is approximately 1.0 \(\times\)\(10^{-14}\)[101]. As temperature increases, Kw initially decreases, reaching a minimum of around 250 \({}^{\circ}\)C, and then increases reaching some order of magnitude higher at higher pressure values until the critical point of water at 374 \({}^{\circ}\)C. In supercritical water (above 374 \({}^{\circ}\)C and 22.064 MPa), the dielectric constant decreases, affecting the extent of ionization. This leads to a decrease in Kw compared to subcritical conditions. In subcritical regions, water, due to the high concentration of H\({}_{3}\)O\({}^{+}\) and OH\({}^{-}\), may act as an acid or basic-like catalyst [72]. The catalytic activity of water in this region may accelerate secondary reactions such as hydrolysis, leading to the decomposition of complex structures of tannins [94]. The extracts may contain components of hydrolyzable tannins such as D-glucose, tannic acid, gallic acid, and ellagic acid. These extracts can be used to produce cross-linking additives (e.g., for films) [102; 103; 104]. In turn, the studies of flavonoid extraction from onion skin showed that an increase in the temperature caused quercetin decomposition to additional unidentified components of the extracts [105]. Similarly, [PERSON] et al. discussed the tendency of anthocyanins to degrade in subcritical water [106]. Unlike water, CO\({}_{2}\), ethanol, and methanol are not classified as highly reactive solvents. However, in the case of the alcohols methanol and ethanol under supercritical conditions, the hydrogen bonding and length of chain clusters are reduced, resulting in the breakdown of alcoholic agglomerates to free monomers. The change in polarity of alcoholic molecules may influence their role as nucleophiles and hydrogen donors in side reactions with  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Raw Material** & \begin{tabular}{c} **Solvents; Conditions;** \\ **Efficiency** \\ \end{tabular}  & **AA; TPC; TTC; Specific Compounds Content** & **Analysis Methods** & **Source** \\ \hline
**Pine sapwood and** & CO\({}_{2}\); 50 \({}^{\circ}\)C, 25 MPa; 1.60\% & \ \begin{tabular}{c} n.a.; n.a.; 19.38 mg/g; \\ stilbenes, flavonoids and lignans \\ \end{tabular}  & \begin{tabular}{c} Folin-Cicalteu \\ method \\ TEAC, FID \\ \end{tabular}  & [98] \\
**pnistar** & CO\({}_{2}\); EtOH\({}_{\text{(}01\text{)}}\); 50 \({}^{\circ}\)C, 25 & \ \begin{tabular}{c} n.a.; 7.60\%; 75.61 mg/g; \\ stilbenes, flavonoids and lignans \\ \end{tabular}  & \begin{tabular}{c} Folin-Cicalteu \\ method \\ TEAC, FID \\ \end{tabular}  & [98] \\
**pnistar** & MPa; 4.1\% & \begin{tabular}{c} 4.95 umu TECA/g 1.91 mg TEAC/g; 0.34 mg \\ GAE/g; 0.48 mg CE g; \\ gallic acid, epigallocatechin, epicatechine \\ method, HPLC, ABTS, \\ DPPH \\ \end{tabular}  & \begin{tabular}{c} 4.95 umu TECA/g 1.91 mg TEAC/g; 0.34 mg \\ GAE/g; 0.48 mg CE g; \\ gallic acid, epigallocatechin, epicatechine \\ method, HPLC, ABTS, \\ DPPH \\ \end{tabular}  & \begin{tabular}{c} 4.95 umu TECA/g 9.04 mg \\ GAE/g; 0.48 mg \\ \end{tabular}  & \ \begin{tabular}{c} 6.93 umu TECA/g 9.04 mg \\ GAE/g; 0.48 mg CE g; \\ method, HPLC, ABTS, \\ DPPH \\ \end{tabular}  & \begin{tabular}{c} Folin-Cicalteu \\ method, HPLC, ABTS, \\ DPPH \\ \end{tabular}  & [99] \\
**Pine leaves** & CO\({}_{2}\); EtOH; 50 \({}^{\circ}\)C, 18, & 2.62 uM1 TEAC/cm\({}^{2}\); \\
**(Camellia sinensis L)** & MPa; n.a. & 1.31 mg GAE/cm\({}^{2}\); 0.50 mg TAE/cm\({}^{3}\),no detail & n.a. & [100] \\  & & content of extra provided & \\ \hline
**Spruce bark** & CO\({}_{2}\); 70\% EtOH\({}_{49}\); 40 \({}^{\circ}\)C, & \begin{tabular}{c} n.a.; 690.94 mg/g dry extract; \\ 11.47 mg/g dry extract; \\ ferulic acid, p-counteramic acid \\ \end{tabular}  & \begin{tabular}{c} \\ 11.74 mg/g dry extract; \\ \end{tabular}  &