Flavonols in grapes, grape products and wines: Burden, profile and influential parameters

Abstract

Flavonols are one of the most studied classes of polyphenolic phytochemicals, because of the importance pertaining to their antioxidant potency and other biological activities. Grapes and grape products such as wine constitute an integral part of the human diet, and during the past few years several studies have generated analytical data on the flavonol profile, as well as on the factors that may affect it. To further aid epidemiological research, which is based on composition tables, this review aims at providing an up-to-date compilation of data on the flavonol composition of grapes and some of the principal commodities deriving from them, including grape juices and wines. Information regarding environmental and technological parameters that may influence flavonols in these products is also reported.

Full text

JOURNAL OF
FOOD COMPOSITION
AND ANALYSIS
Journal of Food Composition and Analysis 19 (2006) 396–404
Critical Review
Flavonols in grapes, grape products and wines:
Burden, profile and influential parameters
Dimitris P. Makris
a,
, Stamatina Kallithraka
b
, Panagiotis Kefalas
a
a
Department of Food Quality Management and Chemistry of Natural Products, Mediterranean Agronomic Institute of Chania (M. A. I. Ch.),
P.O. Box 85, 73100, Chania, Greece
b
Vine and Wine Institute, National Agricultural Research Foundation (N.AG.RE.F.), 1, S. Venizelou Str., 14123, Lycovrysi, Athens, Greece
Received 29 July 2004; received in revised form 11 September 2005; accepted 19 October 2005
Abstract
Flavonols are one of the most studied classes of polyphenolic phytochemicals, because of the importance pertaining to their
antioxidant potency and other biological activities. Grapes and grape products such as wine constitute an integral part of the human diet,
and during the past few years several studies have generated analytical data on the flavonol profile, as well as on the factors that may
affect it. To further aid epidemiological research, which is based on composition tables, this review aims at providing an up-to-date
compilation of data on the flavonol composition of grapes and some of the principal commodities deriving from them, including grape
juices and wines. Information regarding environmental and technological parameters that may influence flavonols in these products is
also reported.
r2005 Elsevier Inc. All rights reserved.
Keywords: Flavonoids; Flavonols; Grapes; Grape products; Polyphenols; Wines
1. Introduction
Flavonols constitute a group of flavonoids that vary in
colour from white to yellow and are closely related in
structure to the flavones. They are represented mainly by
kaempferol, quercetin and myricetin, while simple O-
methylated derivatives such as isorhamnetin (quercetin 30-
methylether) are also common (Fig. 1). The major flavonol
compounds that accumulate in plant tissues are glycosides,
found in an almost bewildering diversity of forms (Fig. 2).
The antioxidative effects of flavonols have been of
interest for a considerable time. The specific mode of
inhibition of oxidation is not clear, but they may act by (i)
scavenging lipid alkoxyl and peroxyl radicals by acting as
chain-breaking antioxidants, e.g., as hydrogen donors; (ii)
chelating metal ions, the appropriate structural features
provided; (iii) regenerating a-tocopherol through reduction
of the a-tocopheroxyl radical. The efficiency of flavonols as
antioxidant compounds greatly depends on their chemical
structure, three structural features being the most impor-
tant determinants (Bors, Heller, Michel and Saran, 1990;
Rice-Evans, Miller, Bolwell, Bramley and Pridham, 1995;
Cook and Samman, 1996;Rice-Evans and Miller, 1996;
van Acker, van den Berg, Tromp, Griffoen, van Bennekon,
van der Vijgh and Bast, 1996,Fig. 3):
(a) the o-dihydroxy (catechol) structure in the B ring,
which is a radical target site;
(b) the 2,3-double bond in conjugation with a 4-keto
function, which are responsible for electron delocaliza-
tion from the B ring; and
(c) the additional presence of both 3- and 5-hydroxyl
groups for maximal radical-scavenging potential and
strongest radical absorption.
Further, the o-dihydroxy structure as well as a 4-keto
and 3- or 5-hydroxyl groups are considered essential
functions with respect to chelating metal ions. The ability
of flavonoids to sequester metal ions contributes to their
antioxidative properties, by preventing the formation of
free radicals in the Fenton system.
ARTICLE IN PRESS
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doi:10.1016/j.jfca.2005.10.003

Corresponding author. Tel.: +328210 35056; fax: +328210 35001.
E-mail address: dimitris@maich.gr (D.P. Makris).

The polyphenolic composition of grapes has been
extensively studied in relation to technologically important
constituents, such as flavanols and anthocyanins, but data
on flavonol content are rather scarce. In grapes (V. vinifera
sp.), derivatives of the most commonly encountered
aglycones, including quercetin, myricetin, kaempferol,
and isorhamnetin, have been found. The conjugates are
exclusively 3-O-glycosides, whereas sugar attachment on
other positions of the flavonol skeleton has never been
reported. For isorhamnetin, only glucose derivatives have
been identified, but myricetin, quercetin and kaempferol
may also occur as glucuronides. Furthermore, quercetin
has been found to form conjugates with glucosylgalactose
and glucosylxylose, and kaempferol with glucosylarabinose
and galactose (Spranger, 1992).
2. Flavonol composition in grapes, grape products and by-
products
Oszmianski and Lee (1990) reported that the content of
quercetin 3-O-galactoside in two samples from Concord
and de Chaunac grapes averaged 34.95 mg kg
1
(Table 1).
In a sample from the Napoleon cultivar, quercetin 3-O-
glucoside and quercetin 3-O-glucuronide amounted to
21.6 mg kg
1
(Cantos, Garcı
´a-Viguera, de Pascual Teresa
and Toma
´s-Barbera
´n, 2000). More recently, the analysis of
free and conjugated flavonols, including quercetin, myr-
icetin, kaempferol and isorhamnetin, in two Cabernet
Sauvignon and two Merlot samples from Chile, showed
that their content ranged between 84.6 and 327.9 nmol g
1
(Burns, Gardner, Matthews, Duthie, Lean and Crozier,
2001). In three white grape extracts from Sauvignon Blanc,
Thompson Seedless and Chardonnay, total flavonols were
shown to occur at levels varying from 4.8 to 10.4 mgL
1
,
the average being 8.2 mg L
1
, determined as rutin equiva-
lents (Meyer, Yi, Pearson, Waterhouse and Frankel, 1997).
However, no data on the analytical composition were
reported. The determination of flavonols in five white
Muscadine varieties (V. rotundifolia sp.), after hydrolysis of
the glycosides, showed that total quercetin, myricetin and
kaempferol were between 3.3 and 7.4 mg per 100 g fresh
weight (mean 6.56 mg/100 g), but paradoxically in five
samples from red Muscadine varieties total flavonol level
was lower, ranging from 1.6 to 3.5 mg/100g (mean 2.4 mg/
100 g) (Pastrana-Bonilla, Akoh, Sellapan and Krewer,
2003).
An extensive investigation of Chardonnay pomace
revealed some interesting aspects of the qualitative
composition of flavonols (Lu and Foo, 1999). In particular,
the isolation and structural elucidation of a plethora of
polyphenolic substances demonstrated the presence of
several flavonol glycosides, including quercetin 3-O-gluco-
side, quercetin 3-O-glucuronide, kaempferol 3-O-glucoside,
and kaempferol 3-O-galactoside. A quite wide diversity of
flavonol glycosides was also found in stems from Merlot
grapes (Souquet, Labarbe, Guerneve
´, Cheynier and Mou-
tounet, 2000), where quercetin 3-O-glucuronide, quercetin
3-O-glucoside, kaempferol 3-O-glucoside, myricetin 3-O-
glucoside, and myricetin 3-O-glucuronide were shown to
occur at levels varying from traces to 218 mg kg
1
. Three
raisin samples from Sultinina grapes were reported to
contain quercetin glycosides in the range of
ARTICLE IN PRESS
HO
OH O
OH
O
OH
HO
OH O
OH
O
OH
OH
HO
OH O
OH
O
OH
OH
OH
HO
OH O
OH
O
OH
OMe
Kaempferol Quercetin
Myricetin Isorhamnetin
Fig. 1. Structures of four common flavonol aglycones encountered in plant tissues.
D.P. Makris et al. / Journal of Food Composition and Analysis 19 (2006) 396 –404 397

82.1–121.8 mg kg
1
(mean 105.4 mg kg
1
)(Karadeniz,
Durst and Wrolstad, 2000), and grape molasses in average
1.69 mg L
1
quercetin, but no kaempferol (Karakaya and
Nehir, 1999).
Unlike for grapes, there has been some limited informa-
tion for grape juices regarding their flavonol composition.
Spanos and Wrolstad (1992) reported very low amounts of
quercetin glycosides, in the range of 7.2–9 mgL
1
, but in
another study the analysis of two juice samples showed
flavonol glycoside concentration ranging from 5.7 to
8.6 mg L
1
rutin equivalents (mean 7.15 mg L
1
), although
data on individual flavonols were not provided (Frankel,
Bosanek, Meyer, Silliman and Kirk, 1998). The concentra-
tion of quercetin, myricetin and kaempferol in one sample
of Muscadine grape juice were of the same magnitude,
9.9 mg L
1
(Talcott and Lee, 2002). In red grape juice from
Concord grapes, total flavonols amounted to 22.85 mg L
1
,
their range being from 21.1 to 24.6 mg L
1
rutin
ARTICLE IN PRESS
HO
OH O
OH
O
OH
O
O
H
OH
H
OH
H
H
HO
H
HO
Quercetin 4'-O-glucoside
OH
OH O
O
OH
O
O
O
H
OH
H
OH
H
H
HO
H
HO
O
H
OH
H
HO
H
H
OH
H
HO
Quercetin 3,4'-O-diglucoside
OH
OH O
O
OH
OH
O
O
H
HO
H
HO
H
H
OH
H
H3C
O
HOH
H
OH
H
H
OH
H
O
Quercetin 3-O-rhamnos
y
l
g
lucoside (rutin)
Fig. 2. Three characteristic flavonol glycosides illustrating various combinations of sugar attachment on the flavonol skeleton.
O
A
B
C
2
3
45
6
7
8
2'
3'
4'
5'
6'
O
OH
Fig. 3. Basic ring structure of flavonols with labelling convention.
D.P. Makris et al. / Journal of Food Composition and Analysis 19 (2006) 396 –404398

equivalents (Frankel et al., 1998). However, juices made
from Muscadine grapes had an even higher content in
quercetin, myricetin and kaempferol, which varied from
13.4 to 100.9 mg L
1
(mean 57.15 mg L
1
)(Talcott and
Lee, 2002). Finally, an analytical survey on 92 vinegar
samples revealed that quercetin and isorhamnetin occur at
very low levels (0.0–3.1 mg L
1
), their average value being
1.53 mg L
1
(Garcı
´a-Parilla, Heredia and Troncoso, 1997).
3. Flavonols in wines
3.1. White wines
Some early reports on flavonol glycoside in white wines
demonstrated the presence of quercetin 3-O-glucuronide in
three Spanish wines made from Valdepen
˜as, La Mancha
and Rioja (Alonso, Estrella and Revilla, 1986). No
quantitative data were reported, but claims were made
that concentration was lower than 1 mg L
1
(Table 2).
Similarly, a more recent investigation on a Riesling wine
demonstrated the occurrence of quercetin 3-O-glucuronide
and kaempferol 3-O-glucoside (Baderschnider and Winter-
halter, 2001). Some quantitative results were provided by
Hertog et al. (1993), who showed that the total content of
flavonols in white wines varied from 0.5 to 1.5 mg L
1
.
These values included both glycosides and aglycones of
quercetin and myricetin, determined after hydrolysis. The
presence of quercetin 3-O-glucuronide was confirmed by
Bete
´s-Saura, Andre
´s-Lacueva and Lamuela-Ravento
´s,
(1996), who detected this flavonol glycoside by analysing
31 wine samples from the cultivars Macabeo, Xarel.lo and
Parellada. Its average content was found to be 0.25 mg L
1
.
It was also reported that no rutin, isoquercitrin, kaempfer-
ol 3-O-glucoside, isorhamnetin 3-O-glucoside or quercetin
was detected in any of the wines analysed. In another study
on 47 Spanish sparkling wines made from a blend of
Macabeo, Xarel.lo and Parellada, it was shown that the
concentration of this compound averages 0.35 mg L
1
,
ARTICLE IN PRESS
Table 1
Flavonol composition of grapes, grape juices and grape products and by-products
Product Number of
samples (n)
Compound(s) Range
a
Average
a
References
Red grapes 2 Quercetin 3-O-galactoside,
Quercetin 3-O-glucoside
22.1–47.8 34.95 Oszmianski and Lee (1990)
Red grapes 11 — 1.4–33.5
b
12.89
b
Meyer et al. (1997)
Red grapes 1 Quercetin 3-O-glucoside, — 21.6 Cantos et al. (2000)
Quercetin 3-O-glucuronide
Red grapes 4 Quercetin, Myricetin, 84.6–327.9c
c
162.43
c
Burns et al. (2001)
Kaempferol, Isorhamnetin,
Glycosides thereof
Red grapes
d
5 Quercetin, Myricetin, Kaempferol 1.6–3.5
e
2.4
e
Pastrana-Bonilla et al. (2003)
White grapes 3 — 4.8–10.4
b
8.2
b
Meyer et al. (1997)
White grape pomace 1 Quercetin 3-O-glucoside, — — Lu and Foo (1999)
Quercetin 3-O-glucuronide,
Kaempferol 3-O-glucoside,
Kaempferol 3-O-galactoside
White grapes
d
5 Quercetin, Myricetin, Kaempferol 3.3–7.4
e
6.5
e
Pastrana-Bonilla et al. (2003)
White grape juice — Quercetin glycosides 7.2–9
f
—Spanos and Wrolstad (1992)
White grape juice 2 — 5.7–8.6 7.15 Frankel et al. (1998)
White grape juice 18 Quercetin 3-O-glucuronide — 0.5 Bete
´s-Saura et al. (1996)
White grape juice
d
1 Quercetin, Myricetin, Kaempferol — 9.9 Talcott and Lee (2002)
Red grape juice 2 — 21.1–24.6 22.85 Frankel et al. (1998)
Red grape juice
d
2 Quercetin, Myricetin, Kaempferol 13.4–100.9 57.15 Talcott and Lee (2002)
Red grape stems 1 Quercetin 3-O-glucuronide, — 218 Souquet et al. (2000)
Quercetin 3-O-glucoside,
Kaempferol 3-O-glucoside,
Myricetin 3-O-glucoside,
Myricetin 3-O-glucuronide
Vinegar 92 Quercetin, Isoquercitrin 0–3.1 1.53 Garcı
´a-Parrilla et al. (1997)
Raisins 3 Quercetin glycosides, 82.1–121.8 105.4 Karadeniz et al. (2000)
Kaempferol glycosides
Grape molasses 2 Quercetin — 1.69 Karakaya and Nehir (1999)
a
For grapes, pomace and stems concentration is expressed as mg kg
1
. For juices concentration is expressed as mg L
1
.
b
Concentration is referred to whole grape extract and is expressed as mg L
1
.
c
Content expressed as nmol g
1
.
d
Varieties belonging to V. rotundifolia.
e
Concentration is expressed as mg per 100 g fresh weight.
f
Concentration is expressed as mgL
1
.
D.P. Makris et al. / Journal of Food Composition and Analysis 19 (2006) 396 –404 399

ranging from 0.1 to 1.2 mg L
1
(Satue
´-Gracia, Andre
´s-
Lacueva, Lamuela-Ravento
´s and Frankel, 1999). Further,
in seven Spanish wines made from Malvar, Verdejo,
Albillo, and Chardonnay, total flavonol concentration
varied from 2 to 7 mg L
1
, the average being 4.29 mg L
1
.
In both cases, however, data on the individual metabolites
were not reported. From the analysis of another three
samples from the cultivars Gewurtztraminer, Colomba
Platino and Torre di Giano, no isorhamnetin was detected,
but the sum of quercetin, kaempferol, myricetin, and rutin
was from 0.4 to 2.5 mg L
1
, with a mean value of
1.43 mg L
1
(Simonetti, Pietta and Testolin, 1997). On
the other hand, the examination of 30 Ontario wines made
from Chardonnay, Riesling, Seyval Blanc and Vidal
demonstrated the presence of quercetin at trace levels,
only in wines from Chardonnay (Soleas, Dam, Carey and
Goldberg, 1997). Finally, Talcott and Lee (2002) reported
a mean value of 2.9 mg L
1
for quercetin, myricetin and
kaempferol in a sample of Carlos Muscadine wine.
3.2. Red wines
Salagoı
¨ty-Auguste and Bertrand (1984) examined the
polyphenolic composition of wines made from Cabernet
Sauvignon, Merlot, and Malbec. It was found that in these
three samples quercetin and myricetin had concentrations
that varied from 11 to 20.9 mg L
1
(Table 3). The
examination of certain red wine samples after hydrolysis
showed that quercetin and myricetin contents were within
very similar limits, from 11.6 to 24 mg L
1
(Hertog et al.,
1993). Alonso et al. (1986) demonstrated the presence of
quercetin 3-O-glucuronide in three Spanish wines made
from Valdepen
˜as, La Mancha and Rioja, estimating its
concentration to be around 1 mg L
1
. Quercetin 3-O-
glucuronide, along with several other flavonols including
quercetin 3-O-glucoside, quercetin, myricetin 3-O-gluco-
side, kaempferol 3-O-glucoside and kaempferol, was also
detected in a sample from Sangiovese, with a total
concentration of 65.3 mg L
1
(Ghiselli, Nardini, Baldi
and Scaccini, 1998). In a more detailed investigation on
14 samples made from Cabernet Sauvignon, Merlot,
Zinfandel, and Petit Syrah, quercetin, myricetin and rutin
varied from 9.7 to 54.5 mg L
1
, with a mean of 25.3 mg L
1
(Frankel, Waterhouse and Teissedre, 1995). Total mean
concentrations for these three flavonols in a Petit Syrah
wine were in absolute accordance (Teissedre, Frankel,
Waterhouse, Peleg and German, 1996). The aglycone
quercetin alone was found to occur at relatively low levels
(0.5–5.3 mg L
1
), as shown by the analysis of five samples
made from Gamay Noir, Merlot, Cabernet Sauvignon,
Cabernet Franc, and Pinot Noir (Soleas et al., 1997). In
Chardonnay and Pinot Noir champagnes, quercetin mean
value was even lower, averaging 0.11 mg L
1
(Chamkha,
Cathala, Cheynier and Douillard, 2003). However, in nine
samples from various red cultivars, including Cabernet
Sauvignon, Syrah, Merlot and Tempranillo, quercetin
content was from 0 to 43.1 mg L
1
, whereas no rutin was
detected (Vin
˜as, Lo
´pez-Erroz, Marı
´n-Herna
´ndez and
Herna
´ndez-Co
´rdoba, 2000). Another study on New York
wines also showed that aglycones such as quercetin and
myricetin occur at rather low levels, as they averaged
5.23 mg L
1
(Goldberg, Dam, Carey and Soleas, 2000).
However, an average as low as 5.12 mg L
1
was also
reported for quercetin and one of its principal glycosides,
rutin, in 18 samples from wines from different countries
(Goldberg, Tsang, Karumanchiri, Diamandis, Soleas and
Ng, 1996). Similarly, the mean content of quercetin,
myricetin and quercetin 3-O-glucuronide was 4.17 mg L
1
in two Italian experimental wines (Pellegrini, Simonetti,
Gardana, Brenna, Brighenti and Pietta, 2000). A higher
value of 13.4 mg L
1
for quercetin and rutin was found for
13 wines from Greece (Sakkiadi, Stavrakakis and Har-
outounian, 2001).
The content of flavonols in red wines has always been
much higher when both aglycones and glycoconjugates
were taken into consideration in the determinations. The
analytical survey on 65 wines from different geographic
origins showed that quercetin, myricetin and their glyco-
sides varied from 4.6 to 41.6 mg L
1
. In many samples no
aglycones were detected, a fact attributed to their relative
ARTICLE IN PRESS
Table 2
Occurrence and content of flavonols and flavonol glycosides in white wines
Number of
samples (n)
Compound Range
a
Average
a
References
3 Quercetin 3-O-glucuronide — — Alonso et al. (1986)
— Quercetin, myricetin 0.5–1.5 — Hertog et al. (1993)
31 Quercetin-3-O-glucuronide — 0.25 Bete
´s-Saura et al. (1996)
3 Kaempferol, quercetin, myricetin, rutin 0.4–2.5 1.43 Simonetti et al. (1997)
30 Quercetin Traces — Soleas et al. (1997)
47 Quercetin 3-O-glucuronide 0.1–1.2 0.35 Satue
´-Gracia et al. (1999)
7 — 2–7 4.29 Sa
´nchez-Moreno et al. (2000)
1 Quercetin 3-O-glucuronide, Kaempferol 3-O-glucoside — — Baderschneider and Winterhalter (2001)
1
b
Quercetin, myricetin, kaempferol — 2.9 Talcott and Lee (2002)
a
Values are expressed as mg L
1
.
b
Wine made from grapes belonging to V. rotundifolia sp.
D.P. Makris et al. / Journal of Food Composition and Analysis 19 (2006) 396 –404400

instabilities (McDonald, Hughes, Burns, Lean, Matthews
and Crozier, 1998). Comparative values for quercetin,
myricetin and the conjugates thereof, ranging from 5.3 to
54.2 mg L
1
, were reported by Gardner, McPhail, Crozier
and Duthie (1999), from a more limited amount of
samples, while the determination of conjugated and
unconjugated quercetin, myricetin, kaempferol and iso-
rhamnetin on 16 wines gave a significantly higher mean
value of 93.08 mg L
1
. Important amounts of rutin and
quercitrin (quercetin 3-O-rhamnoside) that ranged from
25.3 to 153.6 mg L
1
(mean 62 mg L
1
) were found in ten
aged red wines from Greece (Arnous, Makris and Kefalas,
2001), and in seven Spanish wines; the total mean flavonol
concentration was 37 mg L
1
(Sa
´nchez-Moreno, Satue
´-
Gracia and Frankel, 2000).
4. Factors affecting flavonol composition
It has long been known that the biosynthetic pathways
involved in flavonoid production in plant tissues are greatly
influenced by sunlight. In this regard, it would be normally
expected that grapes highly exposed to daylight are capable
of increased flavonol biosynthesis. Indeed, a detailed
examination of sunlight exposure and temperature on the
contents of quercetin, myricetin and kaempferol glycosides
revealed that berries (V. vinifera cv. Merlot) from sun-
exposed clusters might contain as much as ten times the
content found in samples obtained from shaded clusters
(Spayd, Tarara, Mee and Ferguson, 2002). It has also been
pointed out that UV-light barriers contribute prominently
in decreasing flavonol glycoside content in berry tissues,
whereas temperature had little or no effect. The signifi-
cance of ultraviolet radiation on flavonol content in grapes
was also illustrated by examinations on post-harvest
treatments. Flavonol content in Napoleon table grapes
was virtually unaffected when samples were stored at 0 1C
over a period of 10 days, but a notable decrease was
observed upon storage under UV-B treatment. By contrast,
increases were seen when berries underwent UV-C treat-
ment (Cantos et al., 2000). The implementation of various
post-harvest gaseous treatments, including modified atmo-
sphere packaging, controlled atmospheres, and intermit-
tent and continuous ozone exposure, showed that flavonol
levels in Napoleon table grapes may be either preserved or
lowered (Arte
´s-Herna
´ndez, Arte
´s and Toma
´s-Barbera
´n,
2003).
Flavonols, particularly when they occur in their degly-
cosylated form, are labile molecules and may be degraded
upon exposure to heat (Makris and Rossiter, 2000),
enzymes (Makris and Rossiter, 2002a), and oxidative
ARTICLE IN PRESS
Table 3
Occurrence and content of flavonols and flavonol glycosides in red wines
Number of samples
(n)
Compound(s) Range
a
Average
a
Reference
3 Quercetin, myricetin 11–20.9 14.97 Salagoı
¨ty-Auguste and Bertrand (1984)
3 Quercetin 3-O-glucuronide — — Alonso et al. (1986)
— Quercetin, myricetin 11.6–24 — Hertog et al. (1993)
14 Quercetin, myricetin, rutin 9.7–54.5 25.3 Frankel et al. (1995)
18 Quercetin, rutin 0.29–17.75 5.12 Goldberg et al. (1996)
1 Quercetin, myricetin, Rutin — 25.3 Teissedre et al. (1996)
5 Quercetin 0.5–5.3 2.51 Soleas et al. (1997)
Kaempferol, quercetin, myricetin, rutin 3.6–51.4 — Simonetti et al. (1997)
65 Quercetin, Myricetin, 4.6–41.6 17.27 McDonald et al. (1998)
Conjugates thereof
1 Quercetin 3-O-glucoside 65.3 65.3 Ghiselli et al. (1998)
Quercetin 3-O-glucuronide
Quercetin
Myricetin 3-O-glucoside
Kaempferol 3-O-glucoside
Kaempferol
7 Quercetin, Myricetin, 5.3–54.2 21.96 Gardner et al. (1999)
Conjugates thereof
2 Quercetin, Myricetin, 2.9–5.4 4.17 Pellegrini et al. (2000)
Quercetin 3-O-glucuronide
7 — 17–68 37 Sa
´nchez-Moreno et al. (2000)
4 Quercetin, Myricetin 2.1–7.7 5.23 Goldberg et al. (2000)
9 Quercetin 0–43.1 17.59 Vin
˜as et al. (2000)
16 Quercetin, Myricetin, 17.6–195.4 93.08 Burns et al. (2000)
Kaempferol, Isorhamnetin,
Conjugates thereof
10 Rutin, Quercitrin 25.3–153.6 62 Arnous et al. (2001)
13 Quercetin, Rutin 2.37–32.41 13.4 Sakkiadi et al. (2001)
4 Quercetin 0.06–0.17 0.11 Chamkha et al. (2003)
a
Values are expressed as mg L
1
.
D.P. Makris et al. / Journal of Food Composition and Analysis 19 (2006) 396 –404 401

chemical species, such as free radicals (Makris and
Rossiter, 2002b). Therefore, it would appear reasonable
that processing and other treatments of grapes and grape
products might afford prominent alteration in the flavonol
profile. Spanos and Wrolstad (1992) reported extensive
hydrolysis of quercetin derivatives when Thompson Seed-
less juice underwent enzymic clarification, while the
amounts of total flavonols in Muscadine juice exhibited
very large variations depending on the method of juicing
(cold-press, hot-press), but also during storage at different
temperatures (Talcott and Lee, 2002). Rutin appeared to be
relatively unaffected during the acetification process of
Sherry wine (Morales, Tesfaye, Garcı
´a-Parilla, Casas and
Troncoso, 2001), but the content declined to undetectable
levels during Sherry vinegar ageing (Tesfaye, Morales,
Garcı
´a-Parilla and Troncoso, 2002). A similar trend was
also seen for isoquercitrin (Garcı
´a-Parrilla, Heredia and
Troncoso, 1999).
In the case of wines, common vinification practices,
including skin contact, stabilization processes and ageing,
are responsible for significant changes in flavonols, from
both a qualitative and a quantitative point of view. Because
flavonols become important constituents of wine only
when production involves extended extraction from skins,
data on flavonol changes during white wine vinification are
rather scarce. Traditional white wine vinification usually
precludes contact of must with grape pomace, and, as a
consequence, extraction of flavonols that are mainly
located in the skins is very limited. In cases where the
must is left in contact with skins, temperature appears to
play an important role in relation to the amounts of
flavonols that can be extracted (Ramey, Bertrand, Ough,
Singleton and Sanders, 1986).
The polyphenolic profile of red wines is fundamentally
different from that of white wines, due to differences in
composition between red and white grapes, as well as the
implementation of different vinification technologies. A
factor of undisputed importance in relation with wine
quality, namely skin contact, appears to be a crucial
determinant for the flavonol profile. During contact of the
pomace with the fermenting must, it was found that there is
a gradual extraction of both flavonol glycosides and
aglycones, which peaks after a period of 8 to 14 days
(Maye
´n, Me
´rida and Medina, 1995;Gil-Mun
˜oz, Go
´mez-
Plaza, Martı
´nez and Lo
´pez-Roca, 1999); this is, however,
accompanied by a decline during the 88 following days.
This course was more characteristic for glycosides, whereas
aglycones exhibited fluctuations, presumably because of
glycoside hydrolysis, although grape variety and quality
were shown to play a moderate role during the first 9 days
of vinification (Burns, Gardner, O’Neil, Crawford, Mor-
ecroft, McPhail, Lister et al., 2000). The technique used for
submerging the pomace into the fermenting must has also
been found to provoke notable changes in myricetin and
rutin concentration (Garcı
´a-Viguera, Bakker, Bellworthy,
Reader, Watkins and Bridle, 1997;Fischer, Strasser and
Gutzler, 2000). Post-fermentation treatments such as fining
with agents, including casein, bentonite, PVPP and
activated charcoal, were found to cause significant reduc-
tion in both flavonol glycosides and aglycones in Sherry
wines (Baro
´n, Mayen, Merida and Medina, 1997).
Factors that may profoundly differentiate flavonol
composition are also those associated with ageing and
storage conditions. Oxygen seems to play a central role, as
supplementation with oxygen during storage decreased
quercetin levels by more than 50% over a period of 6
months (Castellari, Matricardi, Arfelli, Galasi, Amati,
2000). Another study concerned with the evolution of
flavonols upon storage in barrels made from different types
of wood indicated that losses of both glycosides and
aglycones were significantly more pronounced in barrels
made of American oak, in comparison with barrels made
of French and Spanish oaks (Ferna
´ndez de Simo
´n,
Cadahı
´a, Duen
˜as and Estrella, 2003). This finding high-
lighted the impact of the wooden container on the relevant
oxidative reactions, since the levels of oxygen that may
come into contact with the wine through the staves largely
depend on the size of wood pores. Temperature is another
determinant of flavonol evolution, and it was shown that
quercetin levels were always lower in samples stored at
22 1C than those at 12 1C(Castellari, Piermattei, Arfelli and
Amati, 2001).
The investigation of the evolution of both glycosides and
aglycones illustrated to some extent the observed losses,
indicating that the decline in flavonol glycosides is ascribed
rather to hydrolysis, since a commensurate accumulation
of flavonol aglycones was recorded throughout a period of
7 months (Zafrilla, Morillas, Mulero, Cayuela, Martı
´nez-
Cacha
´, Pardo and Lo
´pez-Nicola
´s, 2003). It is also
noteworthy that rutin, which is a glycoside bearing a
disaccharide, exhibited the highest decomposition. How-
ever, flavonols are also able to react with anthocyanins,
yielding a type of polyphenolic compound known as
copigments, and therefore the decrease in flavonols that
is usually seen during wine ageing and storage could also be
attributed to copigmentation phenomena (Boulton, 2001).
5. Conclusions—future prospects
It is a well-established fact and a widely accepted concept
that grapes and wines constitute one of the most important
sources of dietary polyphenolic antioxidants, including a
large variety of both flavonoid and non-flavonoid con-
stituents. Due to clear evidence which has been provided by
epidemiological studies, that moderate wine consumption
may be associated with depressed rates of cardiovascular
disorders and possibly cancer, a significant number of
publications over the past few years have dealt with the
analytical polyphenolic composition of both commodities.
V. vinifera species, however, embrace a large number of
cultivars with a peculiar polyphenolic composition, and
thus comparative assessment is critical for estimating the
actual ingestion of specific classes of polyphenols through
the regular diet. For this reason, it was deemed necessary to
ARTICLE IN PRESS
D.P. Makris et al. / Journal of Food Composition and Analysis 19 (2006) 396 –404402

gather the bibliographic data that have been published so
far, in order to provide a complete insight into the flavonol
composition of grapes and grape products and by-
products, with a view to this being a first step towards
the creation of a database that might be of assistance in
epidemiological research. Emphasis has also been given to
some data that revealed valuable information on the
environmental and technological factors that may signifi-
cantly affect flavonol composition attributes. After critical
evaluation of the data, it could be claimed that further and
more profound research is required for a more complete
elucidation of the flavonol composition and processes that
might affect it. In support of this, the following target
research areas are proposed:
further research on the effects of pedoclimatic condi-
tions on flavonol content and profile in grapes;
advanced investigations on wine and grape by-product
processing conditions, and the mechanisms responsible
for flavonol losses;
studies on the interactions of flavonols with other
constituents, and the nature of products that might
arise under regular conditions of vinification and wine
ageing and storage.
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