Oolichan grease: a unique marine lipid and dietary staple of the north Pacific coast

Oolichan grease, a dietary fat prepared from smelt-like fish, is highly prized by north Pacific coast aboriginal cultures. The composition of oolichan grease is unclear, with one report indicating a high 22:6n-3 content consistent with cold-water marine oils, but another reporting a much lower value. We noted that oolichan grease remains solid up to 15 degrees C, suggesting a low polyunsaturate content. After extracting total lipids from four fresh oolichan fish and four samples of grease, fatty acids were quantitated by high resolution gas chromatography (GC), as were additional samples of fish lipid and grease that were fractionated into triglyceride (TG), phospholipid (PL), and free fatty acids by thin-layer chromatography. In contradistinction to one prior report, we found EPA and DHA in fresh fish total lipids to be 0.9 and 2.2 wt%, respectively, while in the extracted grease, both were reduced to 0.5 wt%. Only the fresh fish PL fraction contained appreciable DHA. The bulk of the grease consisted of saturated fatty acids (30.3 wt%) and mono-unsaturates (55.0 wt%), explaining its high melting point. Excepting its very low omega-6 content (<2 wt%), oolichan grease is quite similar in composition to human adipose TG. Its solid state at environmental temperatures and low peroxidizability index made it suitable for storage and transport, explaining its status as a preferred trade item among regional aboriginal groups.