**5. Extraction methods**

There are a number of methods that have been suggested for extracting oil from flaxseed, most notably mechanical extraction, solvent extraction, supercritical/ subcritical fluid extraction, and extraction with microwave or ultrasonic intervention. The constitution and amount of unsaturated fatty acids and active substances extracted using various techniques typically vary significantly due to the complexity of flaxseed oil. Flaxseed oil is traditionally produced through mechanical pressing, which depends on outside machinery to produce oil. Among the advantages of using mechanical methods to extract flaxseed oil can be mentioned the low cost and equipment, no change in the taste of the oil, acceptable quality, and no need to use chemical compounds for the extraction process [48]. It has been reported that using from the double-screw extrusion preserves the flaxseed oil quality and its ALA contents, but there are also some clear disadvantages, including low yield, high residual oil, and significant reduction in concentration of some of vitamin, phospholipids, phytosterols, and antioxidants [49]. Low extraction efficiency is properly remedied by solvent method, and up to 99% of the oil is obtained. However, there are some concerns that the use of acetone, methanol, petroleum ether, n-hexane dichloromethane, ethanol, and heptane may decrease the purity of oil, influence its physiological activities, and even result in potential issues with food safety and environmental contamination. As a result, instead of producing commercial products, this technology is primarily employed for laboratory-size investigation.

Modern methods of oil extraction have received a lot of attention recently, including supercritical CO2 extraction, microwave-assisted extraction, ultrasound-assisted extraction, and subcritical fluid extraction. Nowadays, one of the modern methods suggested for extracting flaxseed oil is the use of supercritical CO2 fluid extraction

#### **Figure 1.** *Representative extraction methods of flaxseed oil [53].*

*Perspective Chapter: Flaxseed (*Linum usitatissimum *L) – Chemical Structure... DOI: http://dx.doi.org/10.5772/intechopen.108259*

method, which, in addition to the high quality of the oil, preserves the high concentration of omega-3 fatty acids, phenolic compounds, and lignans [50], and the production efficiency is about 25% higher than that in the mechanical method [51]. Using the microwave and ultrasonic-assisted extraction methods compared with the solvent method has significant advantages, including shortening the extraction time, reducing the solvent consumption, thermal damage to the extract, and the loss of bioactive compounds [52]. The commonly used extraction methods are shown in **Figure 1**.
