Description
Extraction of soybean oil
First the soybeans are cut in flakes which are put in a percolation
extractors and immerged with a solvent, normally hexane.
Counterflow is used as extraction system because it gives the
highest yield.
After removing the hexane, the extracted flakes only contain
about 1% of soybean oil and is used as livestock meal or to
produce food products such as soy protein. The hexane is separated
from the soybean oil in evaporators.The evaporated hexane is
recovered and returned to the extraction process.
The hexane free crude soybean oil is then further
purified.
Purification of soybean oil
The crude soybean oil still contains many oil-insoluble and
oil-soluble impurities that needs to be removed. The
oil-insoluble material are removed with filtration and the soluble
materials is removed with different processes including
degumming (removing of phosphatides), alkali refining (washing with
alkaline solution to remove free fatty acids, colorants,
insoluble matter and gums) and bleaching (with activated earth
or activated carbon to remove colour and other impurities.
​TEST METHOD RANGE
Specific gravity USP 0.****0.**2
Refractive index USP 1.****1.**5
Heavy metals, Method II USP 0.**1% max
Iodine value USP **0 - **1
Free fatty acids USP < 2.5 mL of 0.*2 N NaOH
Saponification value USP **0 - **0
Unsaponifiable matter USP < 1.0%
Cottonseed oil USP passes
Peroxide USP *0.0 max
Fatty acid composition USP
palmitate C*6:0 7 - *4
stearate C*8:0 1 - 6
oleate C*8:1 *9 - *0
linoleate C*8:2 *4 - *2
linolenate C*8:3 4 - *1
