Oil is an indispensable ingredient in our daily lives. From using it in food to its application in the manufacturing of cosmetics and as a renewable resource for bio-diesel fuel production, oil is one of the most important commodities in the market currently. Just like its different applications, the methods of oil extraction are also varied.

Types of Oil Extraction Methods
While the solvent extraction method is the most widely-used technique around the world for manufacturing edible oils and fats, there are other processes that are either used in conjunction with solvent extraction or are quickly gaining popularity over solvent extraction.

The extraction methods are usually optimized and designed depending on the desired quality of the final product. Apart from solvent extraction, some of the methods of oil extraction include the following:

Mechanical Extraction (ME): It is one of the oldest ways of oil extraction but is still largely used for procuring finest quality oil of extra virgin quality. During mechanical extraction, the oil seeds are put between barriers and pressure is applied using hydraulic presses and screws to crush them and extract the oil out. While it requires extensively trained experts, it is the most economical way to extract oil out of oilseeds. The residual oil cake from the mechanical extraction process also has many important applications.

Enzyme Assissted Extraction (EAE): The interwoven lignocellulosic and other polymers that makeup plant cell walls function as a barrier to the extraction of those materials. Enzymes are utilized as a pre-extraction step to break down these cellular components and disrupt pores, which makes it easier for the oil to diffuse into the extraction medium. One of the most commonly used enzymes for this process of oil extraction is the fungus Trichoderma. However, one of the most common disadvantages of this process is low yield, and hence it is not widely used in large- scale commercial production of oils.

Ultrasound Assisted Extraction (UAE): With frequencies between 20 and 100 MHz, ultrasound is a specific kind of sound wave that is beyond human hearing. UAE is primarily related to cavitation activity, which causes bubbles to form, grow, and eventually collapse. This collapse has physical, chemical, and mechanical impacts that cause material matrix rupture, facilitate the release of extractable compounds, and facilitate the migration of the solvent into the sample, enhancing the release of target compounds from the matrix into the solvent. Some of the common benefits of UAE are UAE quick extraction times, minimal energy requirements, and great extraction effectiveness.

Microwave Assisted Extraction (MAE): One of the newest and most appealing alternative methods of oil extraction is microwave assisted extraction (MAE). As a result of the microwave treatment, the protein material is denatured, improving the extraction. The microwave's quick heating and destruction of biological cell structure make for quick, efficient extraction that uses little solvent and yields high-quality oil. The lower energy consumption of this technique reduces both the environmental impact and financial costs.

Supercritical Fluid Extraction (SFE): Supercritical fluids are used in SFE to extract
components from the matrix. The term "supercritical carbon extraction method" is occasionally used to describe this procedure. Compressed gases like ethane, propane, ethylene, dinitrogen oxide and carbon dioxide are employed as solvents in this process.

In order to perform SFE, the solvent must be heated above its critical point and at a pressure of more than 1100 psi. It is pumped through the sample at a rate of 10 to 40 volumes per minute. Because it prefers the extraction of low polar lipid molecules over the coextraction of contaminants (heavy metals and organic derivatives), SFE is sometimes favoured. Other solvents, referred to as cosolvents, such as methanol, ethanol, isopropanol, and acetone, can also be employed in SFE, along with supercritical carbon dioxide (SC-CO2). The carbon dioxide used can be recycled, thereby reducing energy consumption and increasing sustainability.

The process of large-scale oil extraction that started somewhere in the 1920s, have undergone a massive transformation. From being a completely manual process that forced oil out of the sources by pressing and grinding them, it has now become a sophisticated mechanism that uses different techniques and automated processes depending on the resultant product. However, despite all the changes and all the different methods of oil extraction, the basic objective of oil extraction remains the same - obtaining the largest amount of oil from the source possible while keeping the source or the oil cake intact for additional uses.

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