They either have a high EPA content and are mainly sourced from anchovies and/or sardines, or they contain a high amount of DHA and are generally sourced from tuna oils.

There is now a growing demand for concentrated oils with high levels of polyunsaturated fatty acids (PUFA), in particular for the supply of concentrated oil capsules that allow reduced catches for an equivalent amount of active product. This is a chemical concentration process that can be complemented by a second enzymatic process.

To obtain oils with a high content of polyunsaturated fatty acids, the oils are first concentrated by a process that transforms the triglycerides (TG) into ethyl esters (EE) involving the use of a solvent such as ethanol. Ethyl esters are an artificial chemical form, they do not occur in nature.

An additional step is possible to return the fatty acids to their natural form (TG). This further concentration is done with the help of enzymes that allow the fatty acids to be returned to the form of triglycerides, a more stable and oxidation-resistant form.