Hydrogenation of a menhaden oil: II. Formation and evolution of the C₂₀ dienoic and trienoic fatty acids as a function of the degree of hydrogenation

Abstract

To complement studies on monoethylenic fatty acids produced from the major polyunsaturated fatty acid (20:5A5,8,11,14,17) during hydrogenation of a menhaden oil of iodine value (IV) 159, the C10 dienoic and trienoic fatty acid isomers of partially hydro‐genated menhaden oils (PHMO) of IV 131.5, 96.5 and 85.5 were isolated by a combination of preparative gas liquid chromatography (GLC), mercuric adduct fractionation, and silver nitrate thin layer chromatography (AgNO3‐TLC). The 20:2 fatty acid methyl esters of the three PHMO samples were transformed to the corresponding alcohols and ozonized in BF3‐MeOH, followed by GLC analysis of the ozonolysis fragments. During the hydrogenation process, re‐sidual ethylenic bonds in the 20:2 isomers tend to migrate both towards the carboxyl group and towards the methyl end of the molecule. The hydrazine reaction results revealed that thetrans ethylenic bonds in the 20:2 and 20:3 isomers were distributed all along the the carbon chain, but thecis ethylenic bonds were more localized in the Δ11,Δ14 and Δ17 positions of the preexisting major menhaden oil component 20:5Δ5,8,11,14,17. Iatroscan analyses on AgNO3‐chromarods revealed that, as a result of the hydrogenation process, almost half of the 20:2 isomers were non‐methylene‐interruptedcis, trans/trans, cis structures.

Hydrogenation of a menhaden oil: I. Fatty acid and C20monoethylenic isomer compositions as a function of the degree of hydrogenation

“…It is therefore of interest also to study the isomer composition of the more unsaturated fractions (diene and triene) in order to characterize the isomerization reactions which occur during the hydrogenation of the highly unsaturated fatty acids. These details will be found in another paper (10).…”

“…At some future time an application to place partially hydrogenated fish oils on the generally recognized as safe (GRAS) list will require detailed knowledge of fatty acid composition. In this and a companion study on dienes and trienes (10), we have used current "state-of-the-art" analytical technology to investigate the fatty acids of products such as may be projected as typical of those produced from menhaden oil.…”

A rapid method for the analysis of hydrogenated fats by GC with IR detection

“…Full crossvalidation (19) was used for evaluation of the models. For all three models, the standard errors of prediction (SEP) decreased significantly until four components were included in the models; inclusion of more components led to only minor reduction in SEP.…”

“…Matrix isolation GC-IR also has been used for the identification of individual isomers in hydrogenated vegetable fats (18). The direct deposition and matrix isolation interfaces have better signal-to-noise ratios than the lightpipe interface, which is a simpler and less expensive construction.The positional and geometrical isomerization of the FA that occurs during hydrogenation of edible oils, and particularly during hydrogenation of fish oils, leads to a large number of FA isomers that are difficult to quantify by simple chromatographic methods (19). The purpose of this work was to develop a simple and rapid method for quantification of the trans FA content in partially hydrogenated (PH) fish oils and PH vegetable oils, using GC with a lightpipe-interfaced IR spectrophotometer as the only detector.…”

“…The positional and geometrical isomerization of the FA that occurs during hydrogenation of edible oils, and particularly during hydrogenation of fish oils, leads to a large number of FA isomers that are difficult to quantify by simple chromatographic methods (19). The purpose of this work was to develop a simple and rapid method for quantification of the trans FA content in partially hydrogenated (PH) fish oils and PH vegetable oils, using GC with a lightpipe-interfaced IR spectrophotometer as the only detector.…”