Dietary supplements rich in n-3 fatty acids can be divided into
two groups: fish liver oils and fish oils. Fish oils are isolated from
the other parts of fish than liver, for example from byproducts such
as viscera, heads and skins. Both fish liver oils and fish oils could
occur in liquid form or in form of convenient soft gelatin capsules.
The determined levels of bound 3-MCPD in fish oils in the range of
1.5e5.5 mg kg1 may be justified by the fact that fish oils used for
production of dietary supplements are usually refined. Related results
were obtained by Kuhlmann (2011). The author determined 3-
MCPD content in the salmon oil dietary supplements at the range of
0.7e13 mg kg1, while the estimated concentration of 2-MCPD was
in the range of 0.1e2.3 mg kg1. The very low ratio of 2-MCPD/3-
MCPD content may be explained by high specifity of the raw material
to obtain the fish oil. Endogenous enzymes (peroxidase, lipoxygenase),
found in fish muscle tissue are potential initiators of
autoxidation. These enzymes may lead to the formation of substances
responsible for highly unpleasant odour of obtained oil.
Thus the pretreatment of the raw material is recommended for
deactivation of enzymes. For this procedure the addition of acids
are usually used, especially acetic or phosphoric acid. Acid pretreatment
of the fish livers also lowers the surface tension and
therefore enables the release of the oil. Some authors (Collier,
Cromie, & Davies, 1991)