Quince (Cydonia oblonga Miller) Fruit (Pulp, Peel, and Seed)
and Jam: Antioxidant Activity
BRANCA M. SILVA,†PAULA B. ANDRADE,†PATRI ÄCIA VALENTA ˜O,†
FEDERICO FERRERES,‡ROSA M. SEABRA,*,†AND MARGARIDA A. FERREIRA§
REQUIMTE, Servic ¸o de Farmacognosia and Servic ¸o de Bromatologia, Faculdade de Farma ´cia,
Universidade do Porto, R. Anı ´bal Cunha, 4050-047 Porto, Portugal, and Research Group on Quality,
Safety and Bioactivity of Plant Foods, Department of Science and Technology, CEBAS-CSIC,
P.O. Box 164, E-30100 Espinardo, Murcia, Spain
To study the antioxidant activity of quince fruit (pulp, peel, and seed) and jam, methanolic extracts
were prepared. Each extract was fractionated into a phenolic fraction and an organic acid fraction
and was analyzed by high-performance liquid chromatography (HPLC)/diode array detection and
HPLC/UV, respectively. Antiradical activities of the extracts and fractions were evaluated by a
microassay using 1,1′-diphenyl-2-picrylhydrazyl. The phenolic fraction always exhibited a stronger
antioxidant activity than the whole methanolic extract. Organic acid extracts were always the weakest
in terms of antiradical activity, which seems to indicate that the phenolic fraction gives a higher
contribution for the antioxidant potential of quince fruit and jam. The evaluation of the antioxidant
activity of methanolic extracts showed that peel extract was the one presenting the highest antioxidant
capacity. The IC50values of quince pulp, peel, and jam extracts were correlated with the caffeoylquinic
acids total content. Among the phenolic fractions, the seed extract was the one that exhibited the
strongest antioxidant activity. The IC50values of quince pulp, peel, and jam phenolic extracts were
strongly correlated with caffeoylquinic acids and phenolics total contents. For organic acid fractions,
the peel extract was the one that had the strongest antiradical activity. The IC50values of quince
pulp, peel, and jam organic acid fractions were correlated with the ascorbic acid and citric acid contents.
Cydonia oblonga Miller; phenolic compounds; organic acids; antioxidant activity; DPPH
In recent years, it has become evident that significant health
risks and benefits are associated with dietary food choice (1).
Fruits and vegetables are rich sources of vitamins, most notably
vitamins A and C, and excellent sources of fiber, contain some
calories, and are naturally low in fat (2). An increased
consumption of fruits and vegetables has been associated with
protection against various diseases, including cancers and cardio-
and cerebrovascular diseases (3). This association is often
attributed to the antioxidants present in the fruits and vegetables,
such as vitamins C and E, carotenoids, phenolic acids, and
flavonoids, which prevent free radical damage (2).
Quince fruit (Cydonia oblonga Miller, Rosaceae family) is a
pome with numerous seeds. The fruits are big (10-12 cm in
diameter), with variable dimensions and asymmetric shapes, and
exhibit a characteristic fragrance. The peel is covered by an
abundant hair, which disappears with fruit ripening. The white-
yellow pulp, easily oxidized to air exposition, is firm, generally
acidic, and astringent; so, it is not suitable for consumption when
raw. The most important utilization of this fruit is in the
production of jams and jellies, which are very appreciated in
Several analytical methods were developed to determine
phenolics, organic acids, and free amino acids in quince fruit
and jams, and their composition, in terms of these compounds,
was established (4-11). Among these parameters, the phenolic
profile determination was revealed to be the most useful in the
discrimination of the different parts of quince fruit (pulp, peel,
and seed) (7, 9) and in the evaluation of the genuineness of
quince puree (4), jam (5, 6), and jelly (12). Recently, the
influence of jam processing upon the contents of phenolics,
organic acids, and free amino acids in quince fruit was also
The antioxidant activity of several fruits has been observed
in different experimental models (2, 14-22). Garcı ´a-Alonso et
al. (22) analyzed 28 different fruits, including quince pulp, for
antioxidant activity determination. Additionally, these authors
tried to correlate the antioxidant activity and the flavanol content
of these fruits. However, information concerning the antioxidant
* To whom correspondence should be addressed. Tel: 351 222078934.
Fax: 351 222003977. E-mail: firstname.lastname@example.org.
†Servic ¸o de Farmacognosia, Universidade do Porto.
§Servic ¸o de Bromatologia, Universidade do Porto.
J. Agric. Food Chem . 2004, 52, 4705−47124705
10.1021/jf040057v CCC: $27.50 ©2004 Am erican Chem ical Society
Published on Web 07/03/2004
potential of quince peels, seeds, and jams is not available. So,
in the sequence of previous works and regarding its chemical
composition, the purpose of this study was to evaluate the
antioxidant potential of quince fruits (pulp, peel, and seed) and
jams. To accomplish this aim, the scavenging effect of quince
fruit (pulp, peel, and seed) and jam methanolic extracts on 1,1′-
diphenyl-2-picrylhydrazyl (DPPH) was studied. The antioxidant
activity exhibited by the extracts will be the result of the action
of different antioxidant compounds (even from distinct chemical
classes) present, with synergies or antagonisms. Considering
this, the methanolic extracts were fractionated into the phenolics
fractions and the organic acids fractions, which were analyzed
by high-performance liquid chromatography (HPLC)/diode array
detection (DAD) and HPLC/UV, respectively, and their anti-
oxidant activity was also evaluated. Correlations between the
antiradical observed effect and the phenolics and organic acids
content were made.
MATERIALS AND METHODS
Samples. Healthy quince fruits were collected in Amarante (Northern
Portugal). Some fruits were separated into pulps, peels, and seeds, and
each part was freeze-dried. Lyophilization was carried out using a
Labconco 4.5 apparatus (Kansas City, MO). Other fruits were used to
prepare quince jams.
One quince jam sample (jam A) was prepared in the laboratory by
boiling fresh quince pulps with sugar (in the proportion of 50:50), for
approximately 90 min. Another quince jam (jam B) was similarly
prepared but using unpeeled quinces.
Standards. The standards were from Sigma (St. Louis, MO) and
from Extrasynthe ´se (Genay, France). Methanol, formic, and hydro-
chloric acids were obtained from Merck (Darmstadt, Germany), and
sulfuric acid was obtained from Pronalab (Lisboa, Portugal). The water
was treated in a Milli-Q water purification system (Millipore, Bedford,
MA). DPPH was from Sigma.
Solid Phase Extraction (SPE) Columns. The ISOLUTE C18
nonend-capped (NEC) SPE columns (50 µm particle size, 60 Å porosity;
Figure 1. HPLC phenolic profile of the quince pulp (A), peel (B), and seed (C). Detection at 350 nm . Peaks: 1, 3-O-caffeoylquinic acid; 2, 4-O-
caffeoylquinic acid; 3, 5-O-caffeoylquinic acid; 4, lucenin-2; 5, vicenin-2; 6, stellarin-2; 7, isoschaftoside; 8, schaftoside; 9, 6-C-pentosyl-8-C-glucoside of
chrysoeriol; 10, 6-C-glucosyl-8-C-pentosideofchrysoeriol; 11, 3,5-dicaffeoylquinic acids; 12, quercetin3-galactoside; 13, rutin; 14, kaem pferolglycoside;
15, kaem pferol3-glucoside; 16, kaem pferol3-rutinoside; 17and18, quercetinglycosides acylatedwithp-coum aricacid; 19and20, kaem pferolglycosides
acylated withp-coum aric acid.
4706J. Agric. Food Chem ., Vol. 52, No. 15, 2004Silva et al.
10 g sorbent mass/70 mL reservoir volume) were purchased from
International Sorbent Technology Ltd. (Mid Glamorgan, United
Methanolic Extracts. Each sample (ca. 1 g for lyophilized pulps,
peels, and seeds and 5 g for jams) was thoroughly mixed with methanol
(3 × 25 mL) (40 °C). The methanolic extract was filtered, concentrated
to dryness under reduced pressure (40 °C) (the extraction efficiency in
relation to fresh matter was variable as follows: 17, 14, 10, 89, and
73% for pulp, peel, seed, jam A, and jam B methanolic extracts), and
redissolved in methanol (1 mL). These solutions were used for the
Organic Acids Fractions. Each sample (ca. 1 g for lyophilized
pulps, peels, and seeds and 5 g for jams) was thoroughly mixed with
methanol (3 × 25 mL) (40 °C). The methanolic extract was filtered,
concentrated to dryness under reduced pressure (40 °C), and redissolved
in acidic water (pH 2.0 with HCl) (ca. 25 mL). The aqueous solutions
obtained were passed through an ISOLUTE C18 (NEC) column,
previously conditioned with 30 mL of methanol and 70 mL of acidic
water (pH 2.0 with HCl). The aqueous extracts were evaporated to
dryness under reduced pressure (40 °C) (ca. 30 min) and redissolved
in acidic water (1 mL). These extracts were used for the organic acids
analysis and DPPH assay.
Phenolic Compounds Fractions. After the elution of organic acids
and other polar compounds with aqueous solvent, the retained phenolic
fraction was eluted with methanol (ca. 50 mL). The extracts were
concentrated to dryness under reduced pressure (40 °C) and redissolved
in methanol (2 mL). These extracts were used for the phenolic
compounds analysis and DPPH assay.
HPLC Analysis of Organic Acids. The separation was carried out
as previously reported (8) with an analytical HPLC unit (Gilson), using
an ion exclusion column Nucleogel Ion 300 OA (300 mm × 7.7 mm)
column. Detection was performed with an UV detector set at 214 nm.
Organic acids quantification was achieved by the absorbance
recorded in the chromatograms relative to external standards. Malic
and quinic acids were quantified together and as malic acid. The other
acids were quantified as themselves.
HPLC Analysis of Phenolics. The extracts (20 µL) were analyzed
as previously described (4-7, 12, 13), on an analytical HPLC unit
(Gilson), using an Spherisorb ODS2 column (25.0 cm × 0.46 cm; 5
µm, particle size). Detection was achieved with a Gilson DAD.
Phenolic compounds quantification was achieved by the absorbance
recorded in the chromatograms relative to external standards. 3-and
4-O-Caffeoylquinic and 3,5-dicaffeoylquinic acids were quantified as
5-O-caffeoylquinic acid. Kaempferol glycoside and kaempferol gly-
cosides acylated with p-coumaric acid were quantified as kaempferol
3-glucoside. Quercetin glycosides acylated with p-coumaric acid were
quantified as quercetin 3-galactoside. The other compounds were
quantified as themselves.
DPPH Method. The antiradical activity of the extracts was
determined spectrophotometrically in an ELX808 IU Ultra Microplate
Reader (Bio-Tek Instruments, Inc.) by monitoring the disappearance
of DPPH at 515 nm, according to a described procedure of Fukumoto
and Mazza (23), although some modifications were made to the original
For each extract, a dilution series (five different concentrations) was
prepared in a 96 well plate. The reaction mixtures in the sample wells
consisted of 25 µL of extract and 200 µL of 150 mM DPPH (dissolved
in methanol). The reaction was conducted at room temperature, until
Figure 2. Phenolic com pounds of quince fruit andjam .
Quince Fruit and JamAntioxidant ActivitiesJ. Agric. Food Chem ., Vol. 52, No. 15, 20044707
no variation of the absorbance was observed. Ascorbic acid was used
as the reference compound. Four experiments were performed in
The antiradical activity was expressed in terms of the amount of
antioxidants necessary to decrease the initial DPPH absorbance by 50%
(IC50). The IC50value for each extract was determined graphically by
plotting the percentage of DPPH scavenging as a function of extract
RESULTS AND DISCUSSION
Fruits and vegetables are one of the main sources of
antioxidants in our diets (2, 14-22). Our previous studies
showed that quince fruit is a good source of phenolic acids,
flavonoids, and organic acids (4-9, 12, 13), which are
considered potent antioxidants (2). To test the antioxidant
activities of quince fruits and jams, we prepared methanolic
extracts of pulps, peels, seeds, and two jams, one of them
prepared with peeled quinces (jam A) and another with unpeeled
fruits (jam B).
Identification and Quantification of Phenolic Compounds
by HPLC/DAD. Quince pulp and jam A extracts presented a
chemical profile composed of six identified phenolic com-
pounds: 3-O-caffeoylquinic, 4-O-caffeoylquinic, 5-O-caf-
feoylquinic, and 3,5-dicaffeoylquinic acids; quercetin 3-galac-
toside; and rutin (Figures 1A and 2), which is in accordance
with previous studies (7, 13). Quince peel and jam B extracts
contained 13 phenolics: the six compounds presented in pulp
and jam A extracts plus kaempferol 3-glucoside, kaempferol
3-rutinoside (Figures 1B and 2), and five not totally identified
compounds (one kaempferol glycoside, two quercetin glycosides
acylated with p-coumaric acid, and two kaempferol glycosides
acylated with p-coumaric acid), as was already observed (7, 13).
Like previously described (9), the seed extract had a different
composition, presenting the referred caffeoylquinic acids plus
several flavone C-glycosides characteristic of this part of the
fruit: lucenin-2, vicenin-2, stellarin-2, isoschaftoside, schafto-
side, 6-C-pentosyl-8-C-glucoside of chrysoeriol, and 6-C-
glucosyl-8-C-pentoside of chrysoeriol (Figures 1C and 2). In
the pulp extract, caffeoylquinic acids represented 98% of the
determined phenolics, with 3-O-caffeoylquinic acid being the
most abundant (46%), while peel extract contained 57% of
flavonol derivatives, with rutin being the major one (25%). The
peel extract had a higher amount of phenolics than that of the
pulp (about five times) (Table 1). Caffeoylquinic acids repre-
sented 50% of the determined phenolics of seed extract, with
5-O-caffeoylquinic acid being the most abundant (20%). This
extract contained 50% of flavone C-glycosides, and the major
one was stellarin-2 (ca. 17%).
The total flavonoid content of jam A extract was 4%, while
that of the jam B was 21% (Table 1), a fact that may be
explained by the high flavonoidic content of the peel, which
was not removed for the preparation of jam B. In quince jam
extract chromatograms at 280 nm (data not shown), it was
possible to observe a peak corresponding to hydroxymethyl-
furfural (HMF). The presence of this compound is not strange,
once it results from sugar decomposition by heating and cooking
Identification and Quantification of Organic Acids by
HPLC/UV. As previously reported (8), pulp, peel, and jam
extracts presented a similar profile composed of seven identified
organic acids: oxalic, citric, ascorbic, malic, quinic, shikimic,
and fumaric acids (Figures 3 and 4). Oxalic acid was the only
compound that was not detected in seed extract.
In pulp, peel, and jam extracts, the sum of malic acid plus
quinic acid always represented at least 95% of the organic acid
content and all other acids were present in very small amounts
(Table 2). The seed extract was very distinct from the others,
in which the sum of malic acid plus quinic acid represented
only 33% of the total content (Table 2). Citric and ascorbic
Table 1. Phenolic Com positionof Quince Pulp, Peel, Seed, and Jam s Extracts (m g of Phenolic Com pound kg-1of Methanolic Extract Dry Matter)a
pulp peelseedjamA jamB
phenoliccom poundsm ean SDm eanSD m ean SDm ean SDm ean SD
aValues areexpressedas m eans ofthreedeterm inations; SD, standarddeviation; ∑, sumofthedeterm inedphenolic com pound; ND, notdetected; NQ, notquantified;
jamA, quince jampreparedwithpeeledfruits; jamB, quince jampreparedwithunpeeledfruits; 3-CQA, 3-O-caffeoylquinic acid; 4-CQA, 4-O-caffeoylquinic acid; 5-CQA,
5-O-caffeoylquinicacid; 3,5-diCQA, 3,5-dicaffeoylquinicacid; Q-3-Gal, quercetin3-galactoside; Q-3-Rut, rutin; K-Gly, kaem pferolglycoside; K-3-Glu, kaem pferol3-glucoside;
K-3-Rut, kaem pferol 3-rutinoside; Q-gly-p-CouA1 and Q-gly-p-CouA2, quercetinglycosides acylated withp-coum aric acid; K-gly-p-CouA1 and K-gly-p-CouA2, kaem pferol
glycosides acylated withp-coum aric acid; HMF, hydroxym ethylfurfural.
4708J. Agric. Food Chem ., Vol. 52, No. 15, 2004 Silva et al.
acids were also present in great percentages (36 and 31%,
respectively). The organic acid total content of seed extract was
Antioxidant Activity Determination by DPPH Assay. Once
methanolic and acid water extracts (pH 2.0 with HCl) were used,
it was necessary to determine the IC50of ascorbic acid solutions
(1 mg mL-1), dissolved in methanol and acidic water (pH 2.0
with HCl). The ascorbic acid solution IC50value, 5.6 µg mL-1,
was not affected by the solvent.
In what concerns the antioxidant activities of methanolic
extracts, the peel extract was the one that showed the strongest
antioxidant activity (IC50of 0.6 mg mL-1), followed by pulp
and seed extracts, with very similar activities (IC50of 1.7 and
2.0 mg mL-1, respectively) (Table 3 and Figure 5A). Jam A
and B extracts also had similar antiradical activities (IC50of
8.9 and 8.4 mg mL-1, respectively) (Table 3 and Figure 5B).
The results obtained seem to indicate that the IC50of quince
pulp, peel, and jam methanolic extracts is correlated with the
caffeoylquinic acids total content (exponential decay; r )
0.99350; p < 0.05). The seed extract exhibited a different
behavior, probably because of its different composition, in terms
of phenolics (presence of flavone C-glycosides and absence of
flavonols) and in terms of organic acids (different individual
organic acids percentages and lower organic acid total content).
Among the phenolic extracts, the seed extract was the one
that showed the strongest antioxidant activity (IC50of 0.1 mg
mL-1), followed by the peel extract with an IC50 of 0.4 mg
mL-1and the pulp extract with an IC50of 1.0 mg mL-1(Table
3 and Figure 6A). Jam A and B extracts had similar antiradical
activities (IC50of 7.0 and 6.0 mg mL-1, respectively) (Figure
6B). The IC50values of quince pulp, peel, and jam phenolic
extracts were strongly correlated with the caffeoylquinic acids
Figure3. HPLC organic acidprofileofthequincepeel. Detectionat214nm . Peaks: 1, oxalic acid; 2, citric acid; 3, ascorbic acid; 4, m alic acid; 5, quinic
acid; 6, shikim ic acid.
Figure 4. Organic acids of quince fruit andjam .
Table 2. Organic Acids Com positionof Quince Pulp, Peel, Seed, and Jam s Extracts (m g of Organic Acid kg-1of Methanolic Extract Dry Matter)a
organicacidsm eanSD m eanSD m eanSD m eanSD m ean SD
m alic+ quinicacids
aValues are expressedas m eans of three determ inations. SD, standarddeviation; ∑, sumof the determ inedorganic acids; NQ, notquantified; ND, notdetected; jam
A, quince jamprepared with peeled fruits; jamB, quince jamprepared with unpeeled fruits.
Table 3. IC50Values (m g m L-1), Phenolics, andOrganic Acids Total
Contents (m g kg-1) of Quince Pulp, Peel, Seed, and Jam s Extractsa
sam ples IC50
aJamA, quince jampreparedwithpeeledfruits; jamB, quince jamprepared
with unpeeled fruits.
Quince Fruit and JamAntioxidant ActivitiesJ. Agric. Food Chem ., Vol. 52, No. 15, 2004 4709
total content (exponential decay; r ) 0.99793; p < 0.05) and
phenolics total content (exponential decay; r ) 0.99234; p <
0.05). The antioxidant activity of caffeoylquinic acids can be
explained by the presence of a catechol group (Figure 2), which
confers a great stability to phenoxyl radicals by participating
in electron delocalization (24). Additionally, the conjugated
double bond in the side chain of a catechol group is likely to
have a great effect in stabilizing the putative phenoxyl radical
and, therefore, in enhancing antioxidant activity (24). Laranjinha
et al. have already reported the antioxidant activity of chloro-
genic acid (24). Any correlation between IC50 and flavonol
glycosides total content was not found. These results are in
accordance with those of Burda and Oleszek (25), who have
done a comparison of the antioxidant activity of flavonol
aglycons with the activity of its glycosides derivatives and
verified that the blockage of the C-3 hydroxyl group resulted
in a total loss of antioxidant activity. Glycosylation of other
flavonol hydroxyls did not produce such an effect (25). The
antioxidant activities of quercetin and kaempferol and some of
its derivatives have already been reported by some authors (25,
26). Probably, the seed extract had a different behavior because
of its different phenolic composition. As previously referred,
the seed extract had three C-glycosyl apigenin derivatives
(vicenin-2, isoschaftoside, and schaftoside), one C-glycosyl
luteolin derivative (lucenin-2), and three C-glycosyl chrysoeriol
derivatives (stellarin-2, 6-C-pentosyl-8-C-glucoside of chryso-
eriol, and 6-C-glucosyl-8-C-pentoside of chrysoeriol). As can
be seen in Figure 2, these compounds are characterized by the
presence of a hydroxyl group in position 4′ of the B ring, a
2,3-double bond in conjunction with the 4-oxo group in the C
ring, and 5,7-dihydroxyl groups in the A ring. This chemical
structure determines the radical scavenging effect of flavonoids
(25, 26). The presence of the ortho-dihydroxy substitution
pattern in the B ring, as it happens with luteolin derivatives, is
important for the antioxidant activity as well (26). Burda and
Oleszek (25) and Rice-Evans et al. (26) have already reported
the antioxidant activity of luteolin and apigenin and some of
its derivatives. However, the presence of methoxyl substituent
in certain positions, as occurs in chrysoeriol, can also increase
the antiradical activity of flavonoids (25).
Concerning the organic acid extracts, the peel extract was
the one that had the strongest antiradical activity (IC50of 6.9
mg mL-1), followed by pulp and seed extracts with very similar
activities (IC50of 11.6 and 12.9 mg mL-1, respectively) (Table
3 and Figure 7A). Jam B exhibited a stronger antioxidant
activity than jam A, with IC50values of 16.3 and 22.6 mg mL-1,
respectively (Table 3 and Figure 7B). The IC50values of quince
pulp, peel, and jam organic acid extracts were correlated with
the ascorbic acid content (exponential decay; r ) 0.99320; p <
0.05) and citric acid content (exponential decay; r ) 0.98684;
p < 0.05). L-Ascorbic acid is a R-keto lactone with an almost
planar five-membered ring (Figure 4). It has a double bond
between the C-2 (or R) and the C-3 (or ?) carbons, with the
two chiral centers at positions 4 and 5 providing four stereo-
isomers (27). The acidic nature of vitamin C in aqueous solution
derives from the ionization of the enolic hydroxyl on C-3, the
resulting ascorbate anion being delocalized. The reversible
oxidation-reduction with dehydro-L-ascorbic acid is L-ascorbic
acid’s most important property and the basis for its known
physiological activities and stabilities (27). Unlike the oxida-
tion-reduction reactions in which ascorbate donates two
electrons, the antioxidant reactions use their ability to donate a
single electron to free radical species (27). Comparing the
ascorbic acid content of each organic acid fraction corresponding
to IC50(1.3 µg mL-1for pulp and peel extracts, 0.6 and 0.9 µg
Figure5. Antiradicalactivityofquincepulp, peel, andseed(A) andjam s
A and B (B) m ethanolic extracts.
Figure6. Antiradicalactivityofquincepulp, peel, andseed(A) andjam s
A and B (B) phenolic fractions.
4710J. Agric. Food Chem ., Vol. 52, No. 15, 2004Silva et al.
mL-1for jams A and B extracts) with that of ascorbic acid
solutions (5.6 µg mL-1), it seems that vitamin C was not the
only compound that contributed to antiradical activity. In fruits,
citric acid protects ascorbic acid from metal-catalyzed oxidation,
once it is a chelating agent (28). Citric acid functions as a
synergist with other antioxidants (28). Once the seed extract
exhibited great ascorbic and citric acids contents, a lower IC50
value was expected, which did not occur probably due to the
lower malic and quinic acid contents of this extract, which
results in a small organic acid total amount. The ascorbic acid
content of the corresponding IC50was 7.3 µg mL-1, higher than
5.6 µg mL-1, which may suggest the presence of compounds
with prooxidant activity.
Because of the complex compositions of quince fruits and
jams, interactions between different antioxidant components are
likely important in terms of the overall antioxidant activity of
quince fruit and jam. A comparison was made of the antiradical
activity of the whole extracts (methanolic extracts) with that of
its two fractions. The phenolic fraction always exhibited a
stronger antioxidant activity than the whole extracts. Organic
acid extracts were always the weakest in terms of antiradical
activity, which seems to indicate that the phenolic fraction gives
a higher contribution for the antioxidant potential of quince fruits
and jams. The antioxidant activities of the analyzed samples
cannot only be attributed to their phenolic and/or organic acid
contents but to the result of the action of different compounds
present in quince fruits and jams and to possible synergic and
antagonist effects still unknown. Different amounts and types
of minerals can also influence the antioxidant activity of the
quince fruits and jams.
In conclusion, this study suggests that phenolic compounds
are the main antioxidants in quince. This fruit and its jam can
be used as good sources of antioxidants in our diet and may
have relevance in the prevention of diseases in which free
radicals are implicated. Additionally, quince jam byproducts
(peels and seeds) are a good and cheap source of antioxidants,
which could be industrially exploited.
We thank Branca J. Cardoso for helping with sample prepara-
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Received for review February 5, 2004. Revised manuscript received
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