Extraction of oil from high‐moisture tuna liver by subcritical dimethyl ether: a comparison with different extraction methods

Abstract

Tuna liver, which is currently discarded in fish industry, is a valuable source of marine oil rich in n‐3 polyunsaturated fatty acids (PUFAs), vitamin A and vitamin D. In this study, subcritical dimethyl ether extraction (SDEE) was applied in the extraction of oil from high‐moisture tuna liver. Besides, other different extraction methods including wet reduction (WR), enzymatic extraction (EE), and supercritical carbon dioxide fluid extraction (SFE‐CO₂) were used for comparisons, to assess the effect of different extraction methods on yield, oil quality, flavour (volatile compounds and sensory assessing), vitamin contents and fatty acids composition. Compared with traditional methods, the high‐quality liver oil could be obtained with excellent yields by SDEE and SFE‐CO₂, because they could prevent the oxidation of lipids, and, reduce the damage of PUFAs and vitamins effectively. Besides, only minor differences in volatile compounds and vitamins contents were observed between SDEE‐oil and SFE‐CO₂‐oil, which was attributed to the differences in solubility to the solvents used. The oil with higher contents of vitamin A and α‐vitamin E could be obtained by SDEE. The main limitations of SFE‐CO₂ were energy‐consuming due to high pressure used and the necessary pretreatment of freeze‐drying. However, these drawbacks could be overcome in SDEE because the pressure employed in SDEE was quite low (0.8 MPa) and the freeze‐drying was unnecessary. Therefore, SDEE would be a simple, effective and promising technique to obtain the high quality oil rich in n‐3 PUFAs and vitamins in fish oil industry.

Practical Applications: Subcritical dimethyl ether extraction (SDEE) was a rising technology in oil extraction. It could extract oil from the high‐moisture materials without freeze‐drying under relative low pressure. As we know, freeze‐drying is a necessary pre‐processing in ordinary sub‐ and super‐ critical fluid extraction. The high quality of oil could be obtained by SDEE, similar with the quality of the oil obtained by supercritical fluid extraction, with dramatically declined operational costs.

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