## 3 Processing and Extraction
### Supercritical Fluid Extraction  
Supercritical fluid extraction (SFE) includes the use of solvents at temperatures and pressures above the critical values for temperature and pressure. These conditions exhibit both the gaseous and liquid properties of solvents. SFE is commonly performed using carbon dioxide (CO\({}_{2}\)), as it has a low critical pressure and temperature and is considered non-toxic, non-flammable and not expensive. It is also a non-polar and hydrophobic solvent. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{4}{*}{**Source of Waste**} & \multirow{4}{*}{**Pretreatment**} & \multicolumn{2}{c}{**Extraction Procedure**} \\  & & **(E—Equipment, f—Frequency,** & \\  & & **T—Temperature, P—Power,** & \\  & & **M—Sample Weight,** & \\  & & **S–L—Solid-Liquid Ratio, f—Time,** & \\  & & **S–Solvent)** & & \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Conditions and results of microwave-assisted extraction of bioactive compounds from berry by-products. This is the reason why SFE is mostly used to extract lipid fractions from plant material. SFE also provides high selectivity of extraction which may be modulated by changing the conditions of extraction [129]. Examples of supercritical fluid extraction application are given in Table 9. [PERSON] et al. [130] compared SFE with the SLE of lipid fractions from raspberry, blueberry, blackcurrent, blackberry and strawberry pomaces. Oil yield obtained with SFE was increased compared to SLE only in the case of raspberry and blackberry oils. The study also showed particular fatty acid yields, and despite the general value of the oil yield, applying SFE resulted in higher percentage of FAs for each extract. This proves the better selectivity of SFE towards FAs. [PERSON] et al. [131] studied differences between cold pressing and SFE of raspberry seeds. A higher oil yield was reached when cold pressing was applied, and a lower tocopherol content was observed in oil obtained with SFE. Applying SFE, [PERSON] et al. [132] extracted oils from raspberry, chokeberry and strawberry by-products. Oil yields ranged from 12% for raspberry to 18% for strawberry pomaces. The lipid fraction was collected at particular times of the extraction process. The properties of oil--tocopherol content and fatty acid and pigment composition--were dependent on the oil collection time. [PERSON] et al. [133] studied different conditions of SFE of oil from blackberry seeds and a comparison between SFE and SLE methods. The difference between oil yields under optimum conditions for SFE and SLE was significant. Using propane as a solvent at a temperature of 70 \({}^{\circ}\)C and a pressure of 20 MPa during SFE resulted in a 2.32% oil yield. By comparison, SLE conducted using hexane resulted in a 10.51% oil yield. Antioxidant content was also measured and extracts obtained in SFE with CO\({}_{2}\) as a solvent under optimum conditions were characterized by higher TPC values than oils extracted traditionally. [PERSON] et al. [88] also studied properties of blackberry seed oil extracted using the SFE method. Lipid fraction yield in the case of SFE was similar to the yield when SLE with hexane was applied. SFE resulted in oil with a lower tocopherol content compared to SLE. Despite the results summarized in the Table 9, [PERSON] et al. [134], on the basis of their studies applying SFE in the process of oil isolation from raspberry seeds, concluded that higher oil yields were determined by higher pressure and CO\({}_{2}\) flow rate. [PERSON] et al. [135] obtained polyphenol-rich extracts using SFE in their research. The optimum conditions of the process were 45 MPa, 60 \({}^{\circ}\)C and 120 min, and resulted in a TPC of 24.34 mg GAE/g extract. Impact of Processing Conditions  
Pressure of solvent: In studies which aim was to optimize the SFE method it may be noticed that higher oil and polyphenol rich extract yields were noted when higher (but not the highest possible) pressures were applied [133, 135].