Total phenolics and flavonoids in Bulgarian fruits and vegetables

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D. Marinova, F. Ribarova, M. Atanassova
255
Journal of the University of Chemical Technology and Metallurgy, 40, 3, 2005, 255-260
INTRODUCTION
Phenolics are ubiquitous secondary metabolites
in plants. They comprise a large group of biologically
active ingredients (above 8000 compounds)  from simple
phenol molecules to polymeric structures with molecu-
lar mass above 30000 Da [1]. On the basis of the number
of phenol subunits, the modern classification forms two
basic groups of phenolics  simple phenols and polyphe-
nols. The group of simple phenols contains also the so-
called phenolic acids or phenols with carboxyl group
underlying the specificity of their function. Polyphenols
contain at least two phenol rings. Flavonoids, a subject of
comprehensive studies in recent years, belong to this group.
More than 4000 flavonoids have been identified in dif-
ferent higher and lower plant species [2].
The presence of phenolic compounds in diet was
long regarded as a negative feature because they were
TOTAL PHENOLICS AND TOTAL FLAVONOIDS
IN BULGARIAN FRUITS AND VEGETABLES
D. Marinova, F. Ribarova*, M. Atanassova
National Center of Public Health Protection,
Department of Food Chemistry, Sofia 1431, Bulgaria
*E-mail: f.ribarova@nchmen.government.bg
ABSTRACT
The increasing interest in powerful biological activity of plant phenolics and flavonoids outlined the necessity of
determining their contents in Bulgarian fruits and vegetables.
The study comprised 42 food products  20 fruit and 22 vegetable species.
The total phenolic content was determined by using the Folin-Ciocalteu assay. The content of total flavonoids was
measured also spectrophotometrically by using the aluminum chloride colorimetric assay.
The results of fruits showed the highest total phenolic content in blueberries (670.9 mg gallic acid equivalents
(GAE)/100 g), dogwood berries (432.0 mg GAE/100 g) and sour cherry (429.5 mg GAE/100 g). The greatest total flavonoid
content was revealed in blueberries (190.3 mg catehin equivalents (CE)/100 g). The lowest total phenolics and total
flavonoids were established in peaches (50.9 mg GAE/100 g and 15.0 mg CE/100 g, respectively).
The results of vegetables showed the greatest value of phenolics in green peppers (246.7 mg GAE/100 g) and red
peppers (173.2 mg GAE/100 g). Significant difference was found between total phenolic content in red and spring onions
at almost equal total flavonoid values.
The present paper shows particular specificity not only in the total phenolic and flavonoid content, but also in their
ratio and distribution in the different parts of the studied fruits and vegetables.
Keywords: phenolics, flavonoids, fruits, vegetables.
Received 06 June 2005
Accepted 21 July 2005

Journal of the University of Chemical Technology and Metallurgy, 40, 3, 2005
256
doubted to decrease the availability of nutrients, lead-
ing to lower nutritional value of the product [3]. After
the identification of the French paradox and reveal-
ing that the moderate consumption of red wine (rich in
polyphenols) decreases cardiovascular morbidity rate
among French people, particular emphasis was put on
studying phenolic compounds as food ingredients. A
number of data showed that the presence of phenolics
in foods is particularly important for their oxidative sta-
bility and anti-microbial protection [4, 5].
Phenolics possess a wide spectrum of biochemi-
cal activities such as antioxidant, antimutagenic,
anticarcinogenic, as well as ability to modify the gene
expression [6, 7]. Numerous epidemiological studies
confirm significant relationship between the high di-
etary intake of flavonoids and the reduction of cardio-
vascular and carcinogenic risk [8]. The formulation of
preventive and healthy nutrition requires information
about phenolic and flavonoid composition in plant foods.
Based on numerous evidence on the strong bio-
logical activity of phenolic compounds and on the scar-
city of data for their content in foods the aim of current
study was focused on determination of total phenolic
and total flavonoid content in Bulgarian fruits and veg-
etables.
EXPERIMENTAL
Materials
The study covered 42 food products - 20 fruit
and 22 vegetable species. Randomized market sampling
was applied. The average sample consisted of represen-
tative amounts of three individual samples from respec-
tively different region of origin, in similar stage of bio-
logical development and ripeness. Only samples com-
plying with the requirements of good manufacturing
practice were considered. The sampling lasted one year
according to the seasonality of harvesting for individual
species. All samples data are stated in the sampling pro-
tocol. After removing the non-edible parts the samples
were cut into small pieces and frozen under liquid ni-
trogen. The samples were freeze-dried after one week.
The water content in lyophilized fruits and vegetables
was not more than 3.5 %, providing for safety storage
conditions. The freeze-dried samples were vaccumized
in hermetically sealed packages and stored at 4ºC until
the time of analysis. Lyophilization is applied aiming
to uniform the storage conditions and submit the prod-
ucts for analysis in similar form.
Reagents: Gallic acid, (+)-catechin and Folin
Ciocalteus phenol reagent were purchased from Sigma
Chem. Co. All other chemicals were of analytical grade.
Procedures
Sample preparation
A ground freeze-dried sample of 0.5 g was
weighted and phenolic and flavonoid compounds were
extracted with 50 ml 80 % aqueous methanol on an
ultrasonic bath for 20 min. An aliquot (2 ml) of the
extracts was ultracentrifugated for 5 min at 14000 rpm.
Total phenolic assay
The total phenolic content of fruits and vegetables
were determined by using the FolinCiocalteu assay [9].
An aliquot (1 ml) of extracts or standard solution of
gallic acid (20, 40, 60, 80 and 100 mg/l) was added to
25 ml volumetric flask, containing 9 ml of distilled
deionised water (dd H2O). A reagent blank using dd
H2O was prepared. One millilitre of FolinCiocalteus
phenol reagent was added to the mixture and shaken.
After 5 min, 10 ml of 7 % Na2CO3 solution was added
to the mixture. The solution was diluted to volume (25
ml) with dd H2O and mixed. After incubation for 90
min at room temperature, the absorbance against pre-
pared reagent blank was determined at 750 nm with an
UV-Vis Spectrophotometer Lambda 5. Total phenolic
content of fruits and vegetables was expressed as mg
gallic acid equivalents (GAE)/100 g fresh weight. All
samples were analysed in duplicates.
Total flavonoid assay
Total flavonoid content was measured by the alu-
minum chloride colorimetric assay [10]. An aliquot (1
ml) of extracts or standard solution of catechin (20, 40,
60, 80 and 100 mg/l) was added to 10 ml volumetric
flask containing 4 ml of dd H2O. To the flask was added
0.3 ml 5 % NaNO2. After 5 min, 0.3 ml 10 % AlCl3 was

D. Marinova, F. Ribarova, M. Atanassova
257
added. At 6th min, 2 ml 1 M NaOH was added and the
total volume was made up to 10 ml with dd H2O. The
solution was mixed well and the absorbance was mea-
sured against prepared reagent blank at 510 nm. Total
flavonoid content of fruits and vegetables was expressed
as mg catechin equivalents (CE)/100 g fresh mass.
Samples were analysed in duplicates.
RESULTS AND DISCUSSION
The determined analytical parameters of the to-
tal phenolics method was as follows: limit of detection:
0.4 mg GAE/100 g fresh mass; limit of determination:
1.2 mg GAE/100 g fresh mass; recovery: 97% and re-
producibility (RSD): 2.7 %. The determined analytical
parameters of the total flavonoids method was as fol-
lows: limit of detection: 0.6 mg CE/100 g fresh mass;
limit of determination: 1.8 mg CE/100 g fresh mass;
recovery: 96 % and reproducibility (RSD): 3.7 %. These
results proved the viability of the both used methods to
determine phenolic and flavonoid compounds in fruit
and vegetable extracts.
The results for total phenolic and total flavonoid
content and the ratio total flavonoids/phenolics in the
studied fruits are presented in Table 1. The data clearly
outline the richest phenolics sources  blueberries
(670.9 mg GAE/100 g),
dogwood berries (432.0
mg GAE/100 g) and sour
cherry (429.5 mg GAE/
100 g). Blueberries have
also the highest flavonoid
content (190.3 mg CE/100
g) with ratio of 0.32. This
result enables us to sup-
port the proverb popular
in northern countries
When there are blueber-
ries, we shall not need a
doctor. In dogwood ber-
ries the total flavonoids
have a smaller share of
total phenolics, while in
sour cherries the ratio is
0.32, even slightly greater
than in blueberries. The
discussion of this differ-
ence would have a higher
degree of uncertainty, due
to the small number of
tests. It is clear that phe-
nolic acids prevail in dog-
wood berries, which ex-
plains their sour astringent
taste.
The second group
with high total phenolic
content comprises black-
berries (355.3 mg GAE/
Table 1. Content of total phenolics and total flavonoids in fruits.
Results are presented as mean value of duplicates.
Fruit Latin name Total
phenolics
mg GAE/100g
fresh mass
Total flavonoids
mg CE/100g
fresh mass
Flavonoids/
Phenolics
Pear (unpeeled) Pyris communis 124.7 69.9 0.56
Pear (peeled) Pyris communis 91.0 48.5 0.53
A
pple, yellow
(unpeeled) Malus pumila 99.7
34.8 0.35
A
pple, yellow
(peeled) Malus pumila 75.8
20.9 0.28
A
pple, red
(unpeeled) Malus pumila 125.4
48.6 0.39
A
pple, red
(peeled) Malus pumila 104.3
32.7 0.31
Plum Prunus domestica 303.6 136.2 0.45
A
pple, green
(unpeeled) Malus pumila 118.1
40.4 0.34
A
pple, green
(peeled) Malus pumila 97.5
17.3 0.18
Peach Prunus persica 50.9 15.0 0.3
Blackberry Rubus coesins 355.3 55.5 0.16
R
aspberry Rubus ideaus 178.6 26.6 0.15
Strawberry Fragaria vesca 244.1 69.7 0.29
Sweet cherry Prunus avium 78.8 19.6 0.25
Sour cherry Prunus cerasus
vulgaris 429.5
138.6 0.32
Blueberry Vaccinium myrtilus 670.9 190.3 0.28
F
ig Ficus carica 59.0 20.2 0.34
White grape Vitis vinifera 184.1 36.5 0.2
Black grape Vitis vinifera 213.3 77.1 0.36
D
ogwood berry Cornus mas 432.0 91.4 0.21

Journal of the University of Chemical Technology and Metallurgy, 40, 3, 2005
258
100 g), plums (303.6 mg GAE/100 g) and strawber-
ries (244.1 mg GAE/100 g). In this group the total
flavonoids are found in the greatest ratio in plums
(0.45). We could suppose that this is due to the rich
abundance of
anthocyanidines in combi-
nation with the other fla-
vonoids. The low ratio
(0.16) in blackberries is
probably a result of the
rich spectrum of phenolic
acids. In strawberries the
total flavonoids contribute
one third of the total phe-
nolics, with the ratio simi-
lar to that of blueberries.
Pears analysis pro-
vides very interesting re-
sults. We found the highest
percentage rate of total fla-
vonoids vs. total phenolics
compared to all other stud-
ied fruits. This ratio is the
same for both unpeeled and
peeled pears. The unpeeled
pears showed significantly
greater content of total phe-
nolics and total flavonoids.
The results for unpeeled and
peeled apples are quite simi-
lar. Our data suggest richer
presence of phenolics in the
skin of the fruits. The com-
parative assessment between
red and yellow apples favors
the red ones because of the
greater content of phenolics.
The differences in total fla-
vonoid content, following
the same pattern, are quite
smaller.
The analysis of both
grapes species  white and
black logically revealed
higher content of total phe-
nolics and total flavonoids
Table 2. Content of total phenolics and total flavonoids in vegetables.
Results are presented as mean value of duplicates.
Vegetable
Latin name Total phenolics
mg GAE /100g
fresh mass
Total flavonoids
mg CE /100g
fresh mass
Flavonoids/
Phenolics
Carrot Daucus carota 96.0 26.7 0.28
Celery (leaves) Apium
graveolens 113.0
46.4 0.41
Parsley Petroselium
sativum 188.0
27.2 0.14
Okra Hibisons
eculentus 153.7
49.1 0.32
Tomato S. lycopersicum 76.9 12.8 0.17
R
ed pepper Capsicum
anuum 173.2
13.7 0.08
Green pepper Capsicum
anuum 246.7
27.4 0.11
Salad Lactuca sativa 116.2 76.5 0.66
Lettuce Lactuca sativa
capitata 124.5
97.2 0.78
Kohlr abi
Brassica
oleracae var.
caulorapa 44.9
8.9 0.19
R
ed cabbage
Brassica
oleracae var.
botritis 139.3
23.7 0.17
Brussels sprout
Brassica
oleracae var.
Gemmifera 161.5
33.1 0.20
Broccoli
Brassica
oleracae var.
Italica 101.7
18.8 0.18
R
adish
Raphanus
sativus, var.
Radicula 160.0
48.5 0.30
R
ed onion Allium cepa 154.1 18.7 0.12
Spring onion Allium cepa 120.0 16 .0 0.13
Spring onion
(leaves )
Allium cepa 81 .0
11.7 0.14
Spring onion
(stem) Allium cepa 36.5
2.5 0.07
Leek (leaves) Allium porrum 35.7 3.9 0.11
Leek (stem) Allium porrum 27.7 2.6 0.09
Green bean Phaseolus
vulgaris 35.5
4.1 0.12
Yellow bean Phaseolus
vulgaris 55.7
8.2 0.15

D. Marinova, F. Ribarova, M. Atanassova
259
in red grapes, associated with the higher content of
anthocyanidines.
Peaches show particularly low content of total
phenolics and total flavonoids (50.9 mg GAE/100 g and
15.0 mg CE/100 g, respectively) as well as figs (59.0 mg
GAE/100 g and 20.2 mg CE/100 g, respectively) at al-
most equal ratios  respectively 0.3 and 0.34.
The variation of phenolic compounds content
in the fruits depends on many factors. It is known that
it decreases in the process of fruits development. Thus,
for example, in white-coloured fruits it decreases con-
stantly with the progress of the ripening, while in red-
coloured varieties it increases during the last ripening
stage due to the maximal accumulation of
anthocyanines and flavonols. Although we applied a
very strict selection of the samples in equal ripening
stage we support the opinion that this criterion out-
lines data variations to the greatest extent.
The general assessment of the analytical results
for fruits definitely shows individual specificity of each
studied sample and a rich diverse spectrum of phenolic
compounds differing from the flavonoids group.
Table 2 presents the analytical data for total
phenolic and total flavonoid content of the studied
vegetables. The highest total phenolic content was
found in green peppers (246.7 mg GAE/100g), fol-
lowed by parsley (188.0 mg GAE/100g) and red pep-
pers (173.2 mg GAE/100g). The ratio total flavonoids/
phenolics is comparatively low (about 0.1). The re-
sults suggest rich availability of hydroxycinnamic ac-
ids (chlorogenic acid, ferulic acid, p-coumaric acid,
etc.) presented mainly in esterified form with organic
acids, sugars or lipids in the analyzed vegetable spe-
cies. Comparatively high total phenolic content was
found in brussels sprouts (161.5 mg GAE/100 g), rad-
ishes (160.0 mg GAE/100 g), red onions (154.1 mg
GAE /100 g) and okra (153.7 mg GAE/100 g). Of
these vegetables, the highest total flavonoid content
is detected in okra (49.1 mg CE/100 g) and radishes
(48.5 mg CE/100 g). Parallel high content of both
total phenolics and total flavonoids was found in the
studied salads and lettuces.
The substantial difference in total phenolic con-
tent of red and spring onions should be emphasized
(154.1 mg GAE/100 g vs. 120.0 mg GAE/100 g) at very
close total flavonoids values (18.7 mg CE/100 g vs. 16.0
mg CE/100 g). Different content was also detected in
the different parts of the plant. The green part of the
spring onion has more total phenolics compared to the
white part, while the total flavonoids are more concen-
trated in the green part.
The analytical data for leeks follow the same
pattern concerning the stem and the leaves. The results
for yellow and green beans are also similar. It is clear
that the change in the colouring of the plant is a process
associated with redistribution of phenolics and fla-
vonoids.
The results from the analysis of vegetables show
specific total phenolic and flavonoid content and spe-
cific distribution in the particular representatives, es-
pecially for peppers and onions that are traditional for
Bulgarian diet.
CONCLUSIONS
The presented data for total phenolic and total
flavonoid content are a basis for assessment of the pre-
ventive role of fruits and vegetables against free radicals
effect and will enrich the national food composition
database.
They are a necessary step towards in-depth stud-
ies on the spectrum of multiple phenolics and flavonoids
representatives.
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