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Hydrogenation of a menhaden oil: I. Fatty acid and C 20 monoethylenic isomer compositions as a function of the degree of hydrogenation
Author(s) -
Sebedio J L.,
Ackman R. G.
Publication year - 1983
Publication title -
journal of the american oil chemists' society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.512
H-Index - 117
eISSN - 1558-9331
pISSN - 0003-021X
DOI - 10.1007/bf02669970
Subject(s) - chemistry , menhaden , fatty acid , fractionation , docosahexaenoic acid , iodine value , eicosapentaenoic acid , organic chemistry , polyunsaturated fatty acid , fish oil , biology , fish <actinopterygii> , fishery
US menhaden oil is rich in long‐chain polyethylenic fatty acids, chiefly C 20 (eicosapentaenoic) and C 22 (docosahexaenoic) fatty acids, unlike Canadian herring oil, which is rich in long‐chain (C 20 and C 22 ) monoethylenic fatty acids. An examination of the product fatty acids from hydrogenation of menhaden oil therefore comple‐ments studies previously published for herring oil. During a commer‐cial hydrogenation of menhaden oil, iodine value (IV) 159.0, on nickel catalyst, samples were collected at IV 150.0, 140.0, 131.5, 120.5, 96.5, 90.0 and 84.5. The fatty acid compositions were deter‐mined using a combination of mercuric adduct fractionation and gas liquid chromatographic (GLC) analyses, and the total trans content by infrared spectroscopy. The partial hydrogenation resulted in the disappearance of the pentaenoic and hexaenoic fatty acids, a de‐crease in tetraenes, and a definite increase in trienes, 8.3% at IV 84.5 compared to 4.2% at IV 159.0. The dienoic fatty acids in‐creased to 13.2% at IV 84.5 compared to 4.1% at IV 159.0, and the monoenoic fatty acids increased to 34.2% from 24.0%. No impor‐tant changes in the saturated acids were observed, 43.8% at IV 84.5 compared to 41.6% at IV 159.0. The total trans content varied from 3.4% at IV 150.0 to 45.1% at an IV of 84.5. The isomer composi‐tions of the cis and trans C 20 monoethylenic fatty acids were deter‐mined using a combination of preparative GLC, AgNO 3 thin layer chromatography and ozonolysis. The cis 20:1 acids at IV 84.5 still retained 27.5% of the major isomer (All) originally present at 72%. The parent A5, A8, All, A14 and A17 bonds of the 20:5 originally present could be detected in the cis 20:1 isomers at IV 96.5 but not at IV 84.5. At IV 84.5, 58% of the 20:1 was trans , the major isomer being All (9.4% of total 20.1), accompanied by important quanti‐ties of Δ10 and Δ12, respectively, 6.9% and 6.6% of the total 20:1.