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Determinationof Omega-3 (n-3) andOmega-6 (n-6) FattyAcidComposition
inEveningPrimroseOil, FlaxSeedOil, BlackCurrant Oil, andBorageOil
Essential fatty acids (EFAs) are polyunsaturated fatty acids
(PUFAs) that thehumanbody requires, yet cannot produce, and
thereforemust beobtained throughdietary sources or nutritional
supplements.
α
-
Linolenic acid (LNA) and
γ
-
Linolenic acid
(GLA) are importantOmega-3 (n-3) andOmega-6 (n-6) fatty
acids.Accurate determination andquantitationof theseEFAs,
especially the separationof LNA andGLA, canbe performedby
capillarygas chromatography (GC). TheFAMEWAX
™
column is
ideal toprovide the compositionof theEFAs found in evening
primrose oil, flax seedoil, black currant seedoil, andborage oil.
Why are these fatty acids essential?
The two families of EFAs are theOmega-3 (n-3) series and the
Omega-6 (n-6) series.TheOmega-3 (n-3) series includesLNA,
eicosapentaenoic acid (EPA), anddocosahexaenoic acid (DHA).
TheOmega-6 (n-6) series includes linoleic acid (LA),GLA,
dihommogamma-linolenicacid (DGLA), andarachidonicacid
(AA).
TheseEFAs are nutrients that performkey functions inour
bodies. For example, theydeterminemembrane fluidity and
reactivity, oxidation rate,metabolic rate, and energyproduction.
In addition, they are a factor inmaintainingbody temperature,
insulatingnerves, and cushioningbody tissue. EFAs also are
precursors toprostaglandins, hormone-like substances that are
critical to thebody’s overall healthmaintenance. Prostagland-
ins regulatebloodpressure, blood clotting, stimulationof the
immune system, andgeneral regulationof heart, kidneys, liver,
lungs, andbrain.They are short-livedmolecules and constantly
need tobe replenished.Without EFAs this canbe impossible.
Background
EFAs are similar tovitamins in their importance toone’s overall
health.However, vitamins are required in small dietaryquantities
(µg/day),whereasEFAs are amacronutrient (i.e., necessary in
g/day).A joint study releasedby theFood andAgriculture
Organization and theWorldHealthOrganization recommends
that at least 3%of our daily calorie intakebe in the formofEFA.
1
Polyunsaturatedoils, such as safflower, sunflower, and cornoil
are good sources of LA.Once ingested, LA canbe converted to
the otherOmega-6 acids:GLA, DGLA, andAA.
Green, leafyvegetables and flaxoil are good sources of LNA.
From theLNAprovided inour diets, our bodies canproduce the
otherOmega-3 (n-3) acids: EPA andDHA.
Unfortunately, one’s dietmaynot bewell-fortifiedwith these
food sources.Also, physiological conditions can inhibit the
conversionprocess of LA andLNA to the other essentialOmega-
3 andOmega-6 fatty acids.
1
Therefore, nutritional supplements
canbe used tohelppeople attain the suggesteddaily intake.
Eveningprimrose oil, flax seedoil, black currant seedoil, and
borage oil are rich sources of theseEFAs and are available in
capsules as nutritional supplements.
Anumber of clinical conditions have been treatedwithoils rich
inGLA.Oral dosages of eveningprimrose oil have beenused to
treat premenstrual tension, rheumatoid arthritis, breast disorders,
and atopic eczema.
2
Analysis
Theoilswereobtained from soft-gel capsules of evening
primrose oil, flax seedoil, black currant oil, andborage oil.The
fatswere initially in the formof triglycerides.Theywere
saponified into their free acids and esterified for better volatility
and inertness byGC. Todo this, 5mLof hexane and250µLof
2NKOHwere added to0.24goil. Themixturewas shaken for
2minutes in a closed20mLvial.After settling, the supernatant
was injected.
In the 1980s, packed and capillaryGC, aswell as liquid chroma-
tography (LC),were evaluated for the analysis of EFAs in
eveningprimroseoil and soybeanoil.
2
According toone
reference, “gas chromatographyusing a capillary column (25m,
Carbowax
®
20M)was the best tool for the separationofGLA
(C18:3n6) andLNA (C18:3n3).”
3
Basedon this finding,we used aRestek column—the 30m,
0.25mm ID, 0.25µmFAMEWAX
™
column (cat.#12497)—to
analyze these oils. TheFAMEWAX
™
column contains a
polyethyleneglycol stationaryphase,which is slightlymore
polar than theStabilwax
®
column. TheFAMEWAX
™
column
offers excellent selectivity and efficiency, not only to separate
saturated (C16:0 andC18:0) andmonounsaturated (C18:1n9)
fatty acids from theOmega-3 and -6 fatty acids of interest, but
also to resolve the isomers of linolenic acid (C18:3n3 and
C18:3n6).
We used anHP5890GCwith a flame ionizationdetector (FID)
and a split/splitless injectionport, used in the splitmode,with a
split vent flowof 40mL/min.The inlet linerwas a deactivated
4mm ID split sleeve (cat.#20781). The injector anddetector
portswere set at 225°C and230°C, respectively.The oven
temperature programwas initially set at 165°C for the first 30
minutes, and then increased at a rate of 1.5°C/min to220°C,
where it remained for the last 15minutes.The carrier gaswas
helium and the linear velocityof 40cm/sec.wasmeasured at the
initial temperature.
