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Cottonseed oil

Regulation

Cottonseed oil in Canada must be pressed from the seed of the Gossypium plant. As a single source vegetable oil, 100% cottonseed oil must appear as “cottonseed oil” on the labels of any products sold.

Cottonseed oil sold in the marketplace as an edible product must be processed and refined to eliminate specific components that could present as a food safety hazard. In particular gossypol, a natural pigment present in the cotton seeds that acts as a natural defense mechanism to insects and other predators, can also act a toxin to humans, and can lead to infertility in men.

Extraction

Cottonseed oil, like other vegetable oils, is extracted from the seed of the plant, through either mechanical processes such as crushing or pressing, by or chemical processes such as solvent extraction. Cottonseed oil however, is most commonly extracted commercially via solvent extraction.

Processing

Once the crude oil is extracted, it must be processed and refined before it can be used for consumption, in order to remove impurities, including free fatty acids (FFA), phospholipids, pigments and volatile compounds.

Cottonseed Oil Processing Stages

Crude oil refining process:

Degumming

Degumming is the first step in the refining process to remove phospholipids, gums, waxes and other impurities from the crude oil. The oil is treated with water or dilute acids such as phosphoric acid, which exploits the fact that the phospholipids are attracted to water because of their amphipathic nature, and turns the lipids into hydrated gums. These gums are insoluble in oil and are then separated from the oil using centrifuges. The separated gums are then dried and into emulsifying agents such as lecithin.

Neutralization

The second step in the refining process is the separation of the free fatty acids (FFA) from the oil through alkaline neutralization. Depending on the type of oil being processed, there can be either two or three stages during neutralization, where three stages are done to produce a higher quality oil. Cottonseed oil goes through all three stages of neutralization.

The first stage of neutralization occurs when caustic soda, or sodium hydroxide is added to the oil after being pumped through a strainer and heated to 133ºc. Saponification reaction which neutralizes the oil occurs when the mixture is blended.

During saponification, the positive charge from free fatty acids (FFA) reacts with negatively charged hydroxyl group in the caustic soda to form soap and glycerol. This is known as soapstock and will be separated from the oil.

The second stage of neutralization is the repetition of stage one with the addition of more caustic soda to the mixture.

The final stage is a second wash with water to minimize the level of residual soap in the mixture.

Bleaching

The third stage in the refining process is the removal of any residual soap, gums or pigments through bleaching. The most common bleaching agent employed is bleaching earth, a type of bentonite clay. Once the clay is added, the mixture is agitated, which allows the clay to bind the contaminants in the oil, either physically (eg. Van der Waal forces) or chemically (chemisorption). The mixture is then filtered to remove the clay with the bound contaminants.

Deodorization

The fourth stage in the refining process is deodorization to remove any volatile substances. The molecules are distilled using high pressure team injected through a vacuum system.

Winterization

The fifth stage in the refining process is winterization to remove the saturated triacylglycerols to prevent the oil product from solidifying at low temperatures. The processed oil is stored at a cool environment where the temperature is kept below 5ºc.

Through winterization, the oil will separate into liquid and solid fractions. The solid fraction will be crystallized due to the presence of saturated triacylglycerols. The two fractions are then separated by filtration.

Food Uses

Cottonseed oil is used in the production of edible food products such as cooking oils, salad oils, margarines and shortenings. In the United States, cottonseed oil is used in Procter & Gamble’s Olestra and Olein products as a type of non-digestible fat substitutes used to create creamy textures and rich flavours in fried founds.

Nonfood Uses

For agricultural applications, cottonseed oil generally has the greatest insecticide power among all the vegetable oils. They are traditionally used because of their effectiveness in “hard to treat” pest problems in fruit trees. Cottonseed oil can also be mixed with other insecticides to provide a broader spectrum and increased control on pests. Spider mites, whiteflies and young stages of scales are common pests that can be controlled using cottonseed oil.