Phenolic Compounds in Flaxseed: a Review of Their Properties and Analytical Methods. An Overview of the Last Decade

Abstract

Flaxseed has been used for centuries for oil extraction. In recent years it has attracted considerable interest as a result of studies which attribute potential health benefits to its components. Among the compounds that present biological activity, phenolic compounds are of special interest. The dietary lignan secoisolariciresinol diglucoside (SDG) reaches high concentrations in flaxseed. Flaxseed contains also other phenolic compounds, such as phenolic acids. Considering the importance of the phenolic fraction of flaxseed, high performance analytical methods have been developed to characterize its complex phenolic pattern. The understanding of the nature of these compounds is crucial for their possible exploitation in drugs and functional foods.

Full text

7
Journal of Oleo Science
Copyright ©2014 by Japan Oil Chemists’ Society
doi : 10.5650/jos.ess13135
J. Oleo Sci. 63, (1) 7-14 (2014)
Phenolic Compounds in Flaxseed: a Review of Their
Properties and Analytical Methods. An Overview of
the Last Decade
Wahid Herchi1＊, David Arráez-Román2, Hajer Trabelsi1, Intidhar Bouali1,
Sadok Boukhchina1, Habib Kallel1, Antonio Segura-Carretero2 and
Alberto Fernández-Gutierrez2
1 Laboratoire de Biochimie des Lipides, Département de Biologie, Faculté des Sciences de Tunis, 2092 ELmanar-Tunisia.
2 Department of Analytical Chemistry, Faculty of Sciences, University of Granada, C/Fuentenueva s/n, 18071 Granada, Spain.
1 INTRODUCTION
Flaxseed（Linum usitatissimum L.）is a major oilseed
crop cultivated commercially in various parts of the world,
especially in Canada, China, USA, India, the EU and Argen-
tina1）
. Flaxseed has been used for the production of oil,
paint and other industrial products, and has increasingly
gained particular interest in the human food system due to
its rich nutritional components and medicinal values2）
.
Most of the nutritional and health benefits attributed to
flaxseed are due to its constituent omega-3 fatty acid and
phenolic compounds3）
. The by-product of the flaxseed oil
extraction process is known as defatted flaxseed meal, and
this contains large amounts of dietary fibre, lignans and
proteins. Both flaxseed-derived dietary fibres and lignans
possess human health benefits3）
. In 2006-2007, the world
flaxseed meal production was estimated at 1.4 million
tonnes1）
. Compared to other food, flaxseed possesses rich
phenolic compounds profiles with a high amount of
lignans4）
. The aim of this review is to realize a review on
phenolic compounds of flaxseed bearing in mind their con-
tents, structures and chemical-analytical. In particular,
＊Correspondence to: Wahid Herchi, Laboratoire de Biochimie des Lipides, Département de Biologie, Faculté des Sciences de Tunis,
2092 ELmanar-Tunisia.
E-mail: wahid1bio@yahoo.fr
Accepted September 12, 2013 (recieved for review August 13, 2013)
Journal of Oleo Science ISSN 1345-8957 print / ISSN 1347-3352 online
http://www.jstage.jst.go.jp/browse/jos/ http://mc.manusriptcentral.com/jjocs
starting from the basic studies, the results of researches
developed in the last ten years will be focused.
2 CLASSIFICATION AND CONTENT OF PHENOLIC
COMPOUNDS
Flaxseed（Linum usitatissimum）is a rich source of
lignans that have a broad spectrum of biological activity5）
.
An important phytochemical that has both phytoestrogenic
and antioxidant properties is the secoisolariciresinoldiglu-
coside（SDG）, the major lignan identified in flaxseed2）
. The
plant lignans quantified in flaxseed include secosisolarici-
resinol and matairesinol, although pinoresinol, isolarici-
resinol, and demethoxy-secoisolariciresinol have also been
identified in flaxseed6, 7）
. Flaxseed is still the richest source
of plant lignans due to its high content of secoisolarici-
resinoldiglucoside（SDG）. Moreover, Flaxseed has a large
amount of phenolic acids, containing 800 to 1000 mg of
these compounds per 100 g of seed. Esterified phenolic
acids can reach 300 to 500 mg/100 g of seed8）
. Some
Abstract: Flaxseed has been used for centuries for oil extraction. In recent years it has attracted
considerable interest as a result of studies which attribute potential health benefits to its components.
Among the compounds that present biological activity, phenolic compounds are of special interest. The
dietary lignan secoisolariciresinol diglucoside (SDG) reaches high concentrations in flaxseed. Flaxseed
contains also other phenolic compounds, such as phenolic acids. Considering the importance of the phenolic
fraction of axseed, high performance analytical methods have been developed to characterize its complex
phenolic pattern. The understanding of the nature of these compounds is crucial for their possible
exploitation in drugs and functional foods.
Key words: phenolic compounds, axseed, properties, analytical methods
REVIEW

W. Herchi, D. A.-Román, H. Trabelsi et al.
J. Oleo Sci. 63, (1) 7-14 (2014)
8
studies have shown that soluble and insoluble phenolic
acids constitute 54 and 29％, respectively, of the total phe-
nolic acids in flaxseed flour9）
. Trans-ferulic and trans-cin-
namic acids have been reported to be the major phenolic
acids while trans-caffeic acid; p-coumaric acid, chlorogenic
acid, gallic acid, sinapic acid, protocatechuic acid and p-
hydroxybenzoic acid constitute the minor compounds
found in dehulled and defatted flaxseed9）
. Flaxseed also
contains other phenolic acids such as p-coumaric in the
glucosylated forms and phenylpropanoids such as gentisic,
vanillic, and sinapic acids10）
. Other phenolic compounds of
interest have also been found in flaxseed, e.g. ferulic and
vanillic acid11）
, the hydroxycinnamic acid derivatives, p-
coumaric acid-4-β-glucoside, ferulic acid-4-β-glucoside12）
,
Fig. 1 
(A) Chemical structures of lignans from axseed7). (B) Chemical structures of other phenolic compounds from
axseed3).

Phenolic Compounds in Flaxseed: a Review of Their Properties and Analytical Methods. An Overview of the Last Decade
J. Oleo Sci. 63, (1) 7-14 (2014)
9
and the flavonoid herbacetin diglucoside13）
. Flavonoids
constitute a major part of the phenolic compounds present
in flaxseed, the total flavonoid content of flaxseeds ranges
from 35 to 71 mg/100 g12）
. Flavone C- and O-glycosides are
the main flavonoids found in flaxseed. The structures of
phenolic compounds are diverse（Fig. 1）. Secoisolarici-
resinol diglucoside（SDG）, the main lignan in flaxseed, is
hardly present in an unbound from14）
, but is linked in a
macromolecular structure, called the lignan macromolecule
or lignan complex15）
, as represented in Fig. 2. Early studies
have suggested a straight chain oligomeric structure com-
posed of five secoisolariciresinoldiglucoside（SDG）residues
interconnected by four 3-hydroxy-3-methyl glutaric acid
（HMGA）residues. However, a recent study has shown that
hydroxycinnamic acid glucosides and ferulic acid residues
are connected directly to SDG but that there is no linkage
between HMGA and the hydroxycinnamic acid gluco-
sides16）
. Hydroxybenzoic acids are based on a C6-C1-skele-
ton. Meanwhile, cinnamic acids are a series of trans-phe-
nyl-3-propenoic acids with C6-C3 structures differing in
their ring substitution and are commonly found as conju-
gates. Caffeic acid and its esters and ferulic acid are the
phenolic acids most frequently encountered in flaxseed. In
addition, chlorogenic acid is an ester of caffeoyl and quinic
acids17）
.
3 IMPORTANCE OF PHENOLIC COMPOUNDS
Over the past 10 years, researchers have focused in-
creasing attention on polyphenols, their great abundance
in our diet, and their probable role in the prevention of
various diseases associated with oxidative stress, such as
cancer as well as cardiovascular and neurodegenerative
diseases18）
. Phenolic compounds in flaxseed may function
as blocking or trapping agents for chemically induced
cancers caused by aromatic carcinogens. A continuous
input of these protecting compounds may serve as a buffer
against cell damage by quantitative and qualitative supple-
mentation of endogenous protective systems12）
. One of the
most interesting characteristics of flaxseed is its content of
complex phenols, such as lignans. The most remarkable
one is secoisolariciresinol（SDG）, although isolariciresinol,
Pinoresinol, mataresinol and other derivatives of ferulic
acid are also present19）
. Lignan consumption reduces car-
diovascular risk and inhibits the development of some
types of diabetes2）
. Health benefits of flaxseed lignans
reside in their antioxidant capacity. The antioxidant capac-
ity of SDG is related to the suppression of the oxidant con-
ditions due to oxygen species. SDG diglycoside and its
aglycone, secoisolariciresinol display a very high antioxi-
dant capacity and act as protectors against damage to DNA
and liposomes during the metabolism of colon bacteria
which transform them into mammal lignans20）
. With a focus
on phenolic compounds of flaxseed and in light of their im-
portance, attention should be paid to the fact that this
class of compounds has not been completely characterized
due to the complexity of their chemical nature and the
complexity of the matrix in which they are found.
4 EXTRACTION SYSTEMS OF PHENOLIC
COMPOUNDS IN FLAXSEED
The choice of method for the extraction of phenolic
compounds depends on their molecular structure. Less
polar phenolic compounds can be extracted by hexane but
in contrast, SECO, with a higher polarity, can be extracted
by polar solvents such as aqueous methanol or ethanol21）
.
The modern techniques include: liquid-liquid extraction
（LLE）, supercritical fluid extraction（SFE）, pressurized
liquid extraction（PLE）, microwave-assisted extraction
（MAE）, and ultrasound-assisted extraction（UAE）
22）
. The
particular phenolic findings in flaxseed depend on the ex-
traction performed to analyse them. Various organic sol-
vents followed by hydrolysis treatment have been used in
several studies to promote the release of phenolic com-
pounds. For the analysis of SDG, alkaline hydrolysis with
sodium hydroxide has been reported as an effective
method24）
. However, research to identify some compounds
is still from conclusive, since phenolics such as pinoresinol
or matairesinol have been found after solvent extraction
followed by acid and enzymatic hydrolysis. Extraction
methods vary widely depending on the sample and the
Fig. 2 Chemical structure of the lignan macromolecule from axseed15).

W. Herchi, D. A.-Román, H. Trabelsi et al.
J. Oleo Sci. 63, (1) 7-14 (2014)
10
Time of
analysis
Mobile phase Column Type of
elution Extraction System Detection
system Observations References
50 min A: H2O/3% acetic acid
B = CH3CN
an analytical Nova-
Pak C18 column (150
×3.9 mm inner diam-
eter, Waters)
gradient L L E w it h E tO H/ H2 O
(40:60, v/v, 2 mL) for 4h
at room temperature with
orbital shaking (250 rpm)
UV; NMR and
MS
Lignan content evalu-
ation during flaxs ee d
development (Hano et al. 2006)14)
30 min A: acetonitrile/methanol
mixture (7:5, v/v)
B: isopropanol
Zorbax SB-C18 re-
versed-phase column
(5 µm, 250 mm×4.6
mm, Agilent Tech-
nologies, Wilmington,
DE, USA)
Isocratic TLC extraction with iso-
propanol
UV, DAD
MS, MS/MS
HPLC-APCI
(positive ion
mode)
Lipase-catalys e d
transesterification of
dihydrocaffeic acid with
axseed oil for the syn-
thesis of phenolic lipids
(Sabally et al. 2006)30)
60 min A: Water with 0.1% (v/v)
HOAc
B: acetonitrile (ACN) with
0.1% (v/v) HOAc
X-Terra C18 MS
guard column (Wa-
ters; 3.5 µm particle
size, 4.6×10 mm)
isocratic LLE with
63% (v/v) aq. EtOH.
UV, RMN,
MS, MS/MS
Isolation of secoisolar-
ic ir esin ol diglu co side
(SDG), p-coumaric acid
glucoside (CouAG) and
ferulic acid glucoside
(FeAG) and the linker-
molecule hydroxy-
methyl- glutaric acid
(HMGA).
RP-HPLC-MS elution
profiles of lignan macro-
molecule
(Struijs et al. 2007)13)
40 min A: Water with 0.01% (v/v)
TFA
B: acetonitrile (ACN) with
0.01% (v/v) TFA
X-Terra C18 MS col-
umn (Waters; 5 µm
particle size, 50×100
mm, OBD)
gradient
60 min A: Water with 0.1% (v/v)
HOAc
B: acetonitrile (ACN) with
0.1% (v/v) HOAc
X-Terra C18 MS col-
umn (Waters; 5 µm
particle size, 29×150
mm, OBD)
gradient
60 min A: Water with 0.1% (v/v)
HOAc
B: acetonitrile (ACN) with
0.1% (v/v) HOAc
Tricorn Superdex Pep-
tid e 1 0/300 GL col -
umn (Amersham Bio-
science; 10・300–310
mm, bed volume = 24
ml, optimu m separa-
tion range 100–7000
Da)
Isocratic
35 min B: methanolacetonitrile 1:1
(v/v)
A: 0.1% acetic acid isopro-
panol 99:1 (v/v)
using a 100 mm×
2.1 mm i.d., 3.5 µm,
Agilent Zorbax SB-
C8 column (Agilent
Technologies, Inc.)
gradient Fou r diffe rent extraction
met hods were applied as
follows: alkaline extrac-
tion, mild acid extraction,
a combination of alkaline
and mild acid extraction, or
accelerated solvent extrac-
tion.
HPLC-ESI
-MS/MS (neg-
ative mode)
Identification of 7-hy-
droxymatairesinol in
axseed for the first time
Flaxseed was the most
lignan-rich of the studied
species.
Twenty-four plant lig-
nans were analyzed by
HPLC-MS in axseed
(Smeds et al. 2007)28)
HPLC method and conditions of Struijs et al. (2007)13)
Secoisolariciresinol
diglucoside (SDG),
ester-linked to hydroxy-
methyl- glutaric acid
(HMGA), p-coumaric
acid glucoside (CouAG)
and ferulic acid gluco-
side (FeAG).
Isolation of the frag-
ments of the lignan
macromolecule by pre-
par ative RP HP LC an d
identification by MS and
NMR
(Struijs et al. 2008)32)
HPLC method and conditions of Sabally et al. (2006)30)
HPLC chromatograms
of the reaction compo-
nents of lipase-catalysed
acidolysis of axseed oil
p-coumaric acid , sinapic
acid, ferulic acid
(Karboune et al. 2008)
33)
Table 1 Summary of separation of phenolic compounds in axseed samples using HPLC-MS and HPLC-NMR.

Phenolic Compounds in Flaxseed: a Review of Their Properties and Analytical Methods. An Overview of the Last Decade
J. Oleo Sci. 63, (1) 7-14 (2014)
11
Time of
analysis
Mobile phase Column Type of
elution Extraction System Detection
system Observations References
65 min A: CH3CN
B: water with formic acid
(0.1%)
a BDS Hype rsil C18
(250×4.6 mm) col-
umn
gradient LLE with microwave
irradiation+SPE
UV; MS (ESI),
NMR
Isolation of Secoisolar-
ic ir esin ol diglu co side
from lignan-containing
axseed extract Secoiso-
lariciresinol Digluco-
side: HPLC: retention
time tR = 16.09 min;
product purity, 95.3%.
(Stasevich et al. 2009)
31)
50 min (solvent A): 0.050 mmol
L–1 ammonium acetate in
water
(solvent B): 0.050 mmol
L–1 ammonium acetate in
acetonitrile
guard column, 150
mm×4.6mm, 5µm
column (Agilent).
gradient LLE with methanol H P L C /T O F -
MS
Quantification of lignan
from flaxseed hulls and
embryos.
(Popova et al. 2009)34)
50 min (solvent A): 0.050 mmol
L–1 ammonium acetate in
water
(solvent B): 0.050 mmol
L–1ammonium acetate in
acetonitrile
guard column, 150
mm×4.6mm, 5µm
column (Agilent).
gradient H PL C - ES I -
MS/MS
(negative
mode)
30 min A: 0.5% acetic acid: H2O
B: 0.5% acetic acid: MeOH
Discovery C 18 col-
umn 50 mm×3.0 mm
i. d., 5 µm
gradient LLE with 12 ml of 0.3M
sodium hydroxide in
methanol/water (70/30, v/
v)+ Helix pomatia
β-glucuronidase/sulfatase
UV; ESI-MS Quantification of the
determination of plant
lignans SECO and MAT. (Krajkova et al. 2009)4)
HPLC method and conditions of Struijs et al. (2007)13)
Secoisolariciresinol
diglucoside (SDG)+
her bac etin digluco side
(HDG) moieties ester-
linked by 3-hydroxy-
3-methylglutaric
acid (HMGA)+ p-
coumaric acid glucoside
(CouAG)+ ferulic acid
glucoside (FeAG)
(Struijs et al. 2009)35)
40 min A: 0.1% HCOOH in H2O
B: acetonitrile
Nucleodur RP18 (Ma-
cherey& Nagel), 250
×2 mm, 0.5 µm
gradient LLE with Dichloromethane HP L C/ E SI -
MS
ESI in positive
and negative
ion mode)
Identification and quan-
tification of lignans
compounds in different
organs of axseed
(Hemmati et al. 2010)
36)
50 min A: acetonitrile- water- ace-
tic acid (5:93:2 v/v/v)
B: acetonitrile-water-acetic
acid (40:58:2 v/v/v)
Luna C18, 25cm×4.6
mm, i.d. 5 µm particle
size
isocratic SPE DAD; MS
(ESI in posi-
tive and nega-
tive ion mode)
Caffeic acid, ferulic acid,
lignans. Identification of
caffeic acid in the lignan
molecule
(Kosińska et al. 2011)
17)
35 min A: H2O+0.5% acetic acid
B: ACN
C18 RP analytical col-
umn, 4.6×150 mm,
1.8 µm particle size,
Agilent ZORBAX
Eclipse plus
gradient SPE-Diol (1 g of oil) E S I - T O F
(MS)
Determination of all the
well-known phenolic
compounds of flaxseed
oil
(Herchi et al. 2011)6, 19)
35 min A: (0.1% acetic acid in
high-purity water)
B: (0.1% acetic acid in
Acetonitrile).
150 mm×4.6 mm,
5 µm C18 column
(Gemini, Phe-
nomenex, USA)
gradient Alkaline extraction E S I - T O F
(MS)
Determination of some
phenolic compounds of
axseed hull (Hao and Beta. 2012)37)
50 min A: 0.2% (v/v) TFA in water
B: 100% methanol
a Zorbax SB-C18 re-
versed phase column
(pore size 5 lm, 250
×4.6 mm i.d, Restek
Co., Bellefonte, PA,
USA)
gradient LLE with methanol ESI-MS Determination of all the
well-known phenolic
compounds of axseed. (Alu’datt et al. 2013)38)
30 min A: 0.1% acetic acid in wa-
ter,
B: 0.1% acetic acid in ace-
tonitrile
an ACE 3 C18 col-
umn (100×2.1 mm,
particle size: 3 µm
from Advanced Chro-
matography Tec h-
nologies, Aberdeen,
Scotland)
gradient Alkaline extraction ESI-MS Moder ate heating at did
not degrade phenolic
compounds in axseed (Gerstenmeyer et al.
2013)39)

W. Herchi, D. A.-Román, H. Trabelsi et al.
J. Oleo Sci. 63, (1) 7-14 (2014)
12
phytoestrogen of interest. Flaxseed phenols have usually
been extracted with organic solvents sometimes mixed
with water25）
, but the use of supercritical fluid（SCF）ex-
traction has also been reported26）
. Methods for the extract-
ing and quantifying phenolic compounds in flaxseed are
listed in Table 1.
5 NEW ANALYTICAL METHODS FOR STUDYING
PHENOLIC COMPOUNDS DURING THE LAST
DECADE
Different techniques have been used during the last
decade to study the phenolic compounds in flaxseed and
other food sources. Various chromatography（HPLC）and
Capillary Electrophoresis gas chromatography（CE）with
mass spectrometry（MS）have been found as valuable for
the separation of these compounds. An excellent review by
Herchi et al.27）
provides outstanding information on differ-
ent analytical methods for flaxseed compounds. Identifica-
tion and quantification of phenolic compounds in flaxseed,
based traditionally on HPLC（with different detectors, such
as UV, fluorescence, coulometric electrode-array detec-
tion）and, recently, CE-UV, can be aided today by MS and
NMR, which is a focus of the present review. Table 1 pro-
vides an overview of methodologies used for the analysis of
phenolic compounds in flaxseed extracts. Smeds et al.28）
reported a method for quantifying the major lignan precur-
sors based on a liquid chromatography-tandem mass spec-
trometry（LC-MS/MS High-performance thin-layer chro-
matographic）. The method proved precise and accurate
and could be used for the direct quantitative determination
of SDG both in simple and in complex matrices13）
. Hano et
al.14）
used liquid-chromatography nuclear magnetic reso-
nance spectroscopy-mass spectrometry（LC-NMR-MS）cou-
pling to separate and characterize Lignan phenolic com-
pounds during flaxseed development. Liquid
chromatography/mass spectrometry（LC-MS）has been
widely accepted as the main tool in identification, structur-
al characterization, and quantitative analysis of phenolic
compounds in flaxseed. Using a mass spectrometer for de-
tection offers some undoubted advantages, such as inde-
pendence of a chromo- or fluorophore, lo wer LOD than UV
in most cases, the possibility of gaining structural informa-
tion, and easy separation of coeluting peaks using the in-
formation on mass as a second dimension19, 27, 29）
. The sensi-
tivity of the response in MS clearly depends on the
interface technology used. In LC-MS analysis of phenolic
compounds, atmospheric pressure ionization interfaces, i.e.
APCI and electrospray ionization（ESI）, are used almost
exclusively today, and both positive and negative ionization
are applied. In general, phenolic compounds are detected
with greater sensitivity in the negative ion mode, but the
results from positive and negative ion modes are comple-
mentary, and the positive ion mode shows structurally sig-
nificant fragments30, 31）
. On the other hand, optimal ioniza-
tion depends not only on the interface parameters, but also
on the mobile phase of the liquid chromatography. The mo-
bile-phase composition and its pH also need careful optimi-
sation, as they may influence the ionization efficiency of
the analytes. The selection of the analyser, apart from its
accessibility, is determined by the required sensitivity and
selectivity and the general objectives. LC-atmospheric
pressure ionization（API）-MS typically yields only a single
strong ion, which reduces its ability to make accurate
analyte identifications. In most cases, single-stage MS is
used in combination with UV detection to facilitate the
identification of phenolic compounds in flaxseed samples
with the help of standards and/or reference data. MS/MS
and MSn involve two（or more）stages of mass analysis, sep-
arated by a fragmentation step. TOF MS, which is one of
the most advanced MS analysers, provides excellent mass
accuracy over a wide dynamic range if modern detector
technology is chosen. The latter, moreover, enables mea-
surements of the correct isotopic pattern, providing impor-
tant additional information for the determination of ele-
mental composition19）
. High-resolution spectroscopic
techniques, and particularly NMR spectroscopy, are finding
useful applications in the analysis of complex mixtures of
various food extracts that contain phenols. During the past
decade, proton nuclear magnetic resonance spectroscopy
（NMR）has been successfully used in flaxseed analysis14）
.
Coupled techniques such as LC-NMR or LC-NMR/MS may
provide information on overall composition and enable the
identification of individual phenols in complex matrices14）
.
Although compared with HPLC, CE is a relatively new
Table 2 Summary of optimised conditions of capillary-electrophoresis methods where axseed samples are ana-
lysed. V, voltage; T, temperature, i. d., internal diameter of capillary; Lef, effective length of capillary;
[Buffer]; buffer concentration.
Instrumental Variables Experimental Variables
λd [nm] V [kV] T [℃] i. d. [µm] Lef [cm] tinj [s] Type of Buffer [Buffer]
[mM] pH
Organic
modifiers and
other variables
References
280 15 40 50 72 3 s (0.5 p.s.i) boric acid 100 9.3 −(Rybarczyk et al. 2008)40)
200 25 25 50 64 5 s boric acid 100 10 −(Muller et al. 2008)41)

Phenolic Compounds in Flaxseed: a Review of Their Properties and Analytical Methods. An Overview of the Last Decade
J. Oleo Sci. 63, (1) 7-14 (2014)
13
technique in food analysis. A large variety of foods have
already been analysed by this technique, as CE offers a
good compromise between analysis time and satisfactory
characterization for some types of phenolic compounds in
flaxseed. CE technique can be coupled with different de-
tectors（e.g. UV, electrochemical detectors, MS）. With the
use of mass spectrometric detection, differences in optical
detection need to be considered. First, the separation elec-
trolyte should be volatile, reducing the choice of buffering
system to boric acid. Generally, non-aqueous solvents are
well-suited for hyphenation with MS and add another pa-
rameter to modify selectivity. During the last decade, con-
cerning phenolic compounds present in flaxseed, it is pos-
sible to find reports in which applicative work is carried
out. Here in, the publications including CE are summarized
（Table 2）.
CONCLUSIONS
The methods most commonly used for phenolic determi-
nation in flaxseed are based on HPLC, and recently on CE,
coupled with different detector systems（UV, coulometric）.
Even the literature regarding phenolic compounds of flax-
seed were deeply analyzed, this class of compounds is still
not completely studied, because of the complexity of their
chemical nature and the complexity of the matrix in which
they are found. During the last 10 years, NMR and MS have
become indispensable for studying the qualitative-quanti-
tative profiles of phenols and their oxidative forms.
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