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Krill oil is an extract prepared from a species of antarctic krill, Euphausia superba. Two of the most important nutrients in krill oil are omega-3 fatty acids similar to those in fish oil, and phospholipid-derived fatty acids (PLFA), mainly phosphatidylcholine (alternatively referred to as marine lecithin). Also, antioxidant experimental egg products[clarification needed] with krill oil likely contained astaxanthin, a natural antioxidant.
Several studies have shown toxic residues in Antarctic krill and fish; however, the United States Food and Drug Administration has accepted notices from krill oil manufacturers declaring that krill oil and products derived from it meet the standards for Generally Recognized as Safe (GRAS) status, although the FDA itself has not tested the products.
Difference between krill oil and fish oil
Krill oil is rich with omega-3 fatty acids, mainly Eicosapentaenoic acid (EPA) and Docosahexaenoic acid (DHA), bound mostly to phospholipids. The fatty acid composition in the phospholipids in krill oil has been described in two papers. 
- Kassis, NM; Gigliotti, JC; Beamer, SK; Tou, JC; Jaczynski, J (Jan 2012). "Characterization of lipids and antioxidant capacity of novel nutraceutical egg products developed with omega-3-rich oils.". J Sci Food Agric. 92(1) (1): 66–73. doi:10.1002/jsfa.4542. PMID 21769882.
- Corsolini S, Covaci A, Ademollo N, Focardi S, Schepens P (March 2006). "Occurrence of organochlorine pesticides (OCPs) and their enantiomeric signatures, and concentrations of polybrominated diphenyl ethers (PBDEs) in the Adélie penguin food web, Antarctica". Environmental pollution (Barking, Essex : 1987) 140 (2): 371–82. doi:10.1016/j.envpol.2005.04.039. PMID 16183185.
- Covaci A, Voorspoels S, Vetter W, et al. (August 2007). "Anthropogenic and naturally occurring organobrominated compounds in fish oil dietary supplements". Environmental Science & Technology 41 (15): 5237–44. doi:10.1021/es070239g. PMID 17822085.
- CFSAN/Office of Food Additive Safety (July 22, 2011). "Agency Response Letter GRAS Notice No. GRN 000371". U.S. Food and Drug Administration. Retrieved August 5, 2014.
- CFSAN/Office of Food Additive Safety (January 3, 2008). "Agency Response Letter GRAS Notice No. GRN 000226". U.S. Food and Drug Administration. Retrieved August 5, 2014.
- Grandois LG, Marchioni E, Zhao M, Giuffrida F, Ennahar S, Bindler F (June 2009). "Investigation of natural phosphatidylcholine sources: separation and identification by liquid chromatography - electronspray ionization - tandem mass spectrometry (LC-ESI-MS2) of molecular species". Journal of Agricultural and Food Chemistry 57 (14): 6014–6020. doi:10.1021/jf900903e. PMID 19545117.
- Winther B, Hoem N, Berge K, Reubsaet L (September 2010). "Elucidation of phosphatidylcholine composition in krill oil extracted from Euphausia Superba". Lipids 46 (1): 25–36. doi:10.1007/s11745-010-3472-6. PMC 3024512. PMID 20848234.
- Ali-Nehari, Abdelkader; Kim, Seon-Bong; Lee, Yang-Bong; Lee, Hye-youn; Chun, Byung-Soo (14 November 2011). "Characterization of oil including astaxanthin extracted from krill (Euphausia superba) using supercritical carbon dioxide and organic solvent as comparative method". Korean Journal of Chemical Engineering 29 (3): 329–336. doi:10.1007/s11814-011-0186-2.
- "Krill oil sustainability". Wellwise. Retrieved 2010-12-01.
- Venkatraman JT, Chandrasekar B, Kim JD, Fernandes G (August 1994). "Effects of n-3 and n-6 fatty acids on the activities and expression of hepatic antioxidant enzymes in autoimmune-prone NZBxNZW F1 mice". Lipids 29 (8): 561–8. doi:10.1007/BF02536628. PMID 7990663.