Lecithin sludge (gums)
Crude edible oils contain different of undesirable substances like gums (also named phosphatides or phospholipids), free fatty acids (ffa), traces of metals, colouring components and volatile components. Gums can be removed separately or in an integrated process together the removal of ffa.
There are two types of gums: hydratable and non-hydratable. The hydratable gums can be separated from the oil after mixing with water. These hydratable gums can then be separated from the oil with a centrifuge and added to the meal of an integrated oilseed extraction plant, further processed in order to obtain foodgrade lecithin or sold as a feedstock raw material.
Non hydratable gums and phosphate acids can be separated from the crude oil after acidification of the crude oil with phosphoric acid. Degumming can also operate separately or together with the chemical removal of ffa (chemical neutralisation).
Block diagram of the oil extraction process (for sunflower, soya, and rape seeds)
Degummed oil (i.e. < 30 ppm P in the oil) can also be used for further processing in physical refining processes. Non hydratable gums can also add to the meal and processed to obtain foodgrade lecithin or processed with soapstock.
The value of the by-products (phospholipids) can influence the choice between separate degumming or integrated degumming-ffa removal. When dried, these gums become liquid lecithin. Lecithin has various end uses such as food emulsifier. The precipitated gums can instead be returned to the meal in the extraction plant.