In order to increase EPA and DHA concentration starting from
FOEE, the shortest fatty acid chains (C14–C16–C18) must be separated
from the longest (C20–C22), as well as saturated and
monounsaturated esters from polyunsaturated ones. Separation
on the basis of the degree of unsaturation is typically attained
by means of crystallization processes, which may be performed
in conventional solvents (e.g., methanol, acetone) or in the ureaadduction
process [7]. With regard to the separation on the
basis of chain length, short alkyl esters are classically separated
by distillation processes. However, when dealing with the long
polyunsaturated fatty acid chains of fish oils, the conventional vacuum
distillation is not feasible, because the high temperatures
required (well above 200 ◦C) unacceptably degrade PUFA [7,8].