Soybean Oil: How is it extracted?

Soy is a legume native to China and has been traditionally cultivated in Asia for several centuries. Its seeds are intended for several uses, including the production of vegetable oil. This oil is in turn produced for various applications in the culinary, therapeutic, and cosmetic worlds. There are several methods to extract soy oil from the seeds, the first being cold pressing.

About 3 months after sowing, when they have reached maturity, the soybeans are harvested then cleaned, in order to remove any impurities that may be attached to their surface. They are then dried using a dryer, following the convection process, so that their residual moisture reaches about 10%. Once the beans are sufficiently dry, they are mechanically pressed flat to extract the oil. They are then introduced into a screw press, kept at a temperature below 60°C, hence the term "cold pressing". Finally, the obtained oil is then decanted, filtered or centrifuged to concentrate it.

• Benefits : This method is 100% natural and does not require any chemical solvents. Moreover, the process being carried out at low temperature, the oil is not degraded and retains all its active ingredients. Finally, this technique is respectful of the environment, as it requires little energy and avoids the release of polluting residues.

• Drawbacks : The yield obtained from a cold press is relatively low compared to the use of other techniques.

The vegetable soybean oil used to formulate Typology products has been extracted from the seeds through cold pressing, utilising plants sourced from organic farming.

Soybean oil can also be extracted using hexane, an organic solvent often used for extractions. To do this, after cleaning, the seeds are introduced into an extractor where they are mixed with hexane. The oil then dissolves in the hexane. The mixture is then heated to evaporate the hexane and retain only the soybean oil. This step is carried out in a evaporator, a piece of equipment where the temperature and pressure are controlled in order to best preserve the soybean oil. The oil is then refined to remove impurities.

• Benefits : Hexane extraction allows for a significant yield, of approximately 97%.

• Drawbacks : Hexane is a costly, polluting solvent and poses a significant public healthconcern.

A lesser-known method, the extraction of soybean oil by CO2 in its supercritical state is relatively straightforward to perform. Indeed, when in the so-called "supercritical" state, CO2 possesses a significant transport and extraction capacity. To extract soybean oil using this technique, the seeds are placed in an extractor. A flow of supercritical CO2 passes through the extractor, becomes charged with soybean oil, then transitions to a gaseous phase which allows the separation of the CO2 and the oil. The latter is then collected in a separator.

• Benefits : The CO2 is a natural, non-toxic and readily available compound. This extraction method is gentle and does not alter the soybean oil. Moreover, it does not generate any harmful waste.

• Drawbacks : The equipment required to perform a CO2 supercritical extraction is relatively expensive.

Finally, it is possible tomechanically extract soybean oil from the seeds using enzymes such as cellulase and glucosidase. These act by hydrolysing the lipoproteins, lipopolysaccharides and polysaccharides of the cell wall in order to release the oil. As most enzymes are specific to a unique type of bond, the use of a mix of enzymes with different activities is necessary to degrade all the macromolecules and reach the oil.

• Benefits : This method is fast and requires little solvent. Moreover, it is environmentally friendly and offers a high yield.

• Drawbacks : The costs of enzymes and production are high.

• HITEX. Supercritical CO2: A rapidly developing extraction and fractionation technology. GazetteLabo (2007).

• ERGONUL P. G. & co. Cold pressed soybean oil. Elsevier eBooks (2020).

• Thesis by Lylia CHELLALI & Samhia CHELIT. Use of enzymes in the extraction of vegetable oils (2021).