INTRODUCTION
Tea (Camellia sinensis L.) is considered to be the
most popular beverage in the world [1, 2]. It has been
estimated that the average daily consumption of tea is
approximately 120 mL. Poland is among the first three
European countries and ten world countries in terms of
tea consumption. Of several species commonly referred
to as tea, the most important is Chinese tea produced
from the Camellia sinensis leaves [3]. The chemical
composition of tea is highly diverse and may vary within
a relatively broad range, depending on many factors
(e.g. the position of leaves on the stem, growth
conditions, processing methods, or brewing time) [4–6].
In recent years, of great interest has been the
therapeutic activity of tea and, in particular, the
antioxidant effects of its compounds, e.g. polyphenols
and flavonoids [3, 6–10]. Due to differences in
processing technology or species composition, each type
of tea contains a different combination of biologically
active substances, depending on the extraction time and
temperature, as well as leaf fineness. Fresh green leaves
are rich in isomeric flavan-3-ols (catechins), on average
accounting for 30% of their mass, with epigallocatechin
gallate (EGCG) being the most common component.
During fermentation, some catechins undergo oxidation
and condensation to high molecular weight compounds
(3–6% theaflavins and 12–18% thearubigins) responsible
for the characteristic flavor and aroma of infusions [4, 5,
9, 8, 11, 12].
Our study is an attempt to estimate the effect of
infusions brewing time and storage on the content of
bioactive compounds (polyphenols and flavonoids) and
antioxidant properties of 45 loose-leaf and bagged teas
available on the Polish market.
STUDY OBJECTS AND METHODS
Using the FRAP and DPPH methods, we compared
the total content of polyphenols and flavonoids, as well
as the antioxidant properties of infusions made from
several types of loose-leaf (L) and bagged (E) teas
available on the Polish market. Additionally, we assessed
the effects of the brewing time and storage of infusions
on the total content of polyphenols and antioxidant
properties.
The research material consisted of 45 teas
produced commercially by leading manufacturers
Research Article DOI: http://doi.org/10.21603/2308-4057-2020-1-91-97
Open Access Available online at http://jfrm.ru/en/
Changes of antioxidant activity
and active compounds content in selected teas
Barbara Kolodziej* , Danuta Sugier, Katarzyna Luchowska
University of Life Sciences, Lublin, Poland
* e-mail: barbara.kolodziej@up.lublin.pl
Received September 05, 2019; Accepted in revised form January 13, 2020; Published February 25, 2020
Abstract: Our study tested 45 tea infusions classified into five groups (white, green, red, black, and other teas) for the content of total
polyphenols and flavonoids, as well as antioxidant properties, by the FRAP and DPPH methods. We examined these parameters after
prolongation of the brewing time from 10 to 30 min and overnight storage. The results showed that the capacity of the teas to bind
free radicals was differentiated and the amount of anti-oxidant compounds depended on their nature. In terms of antioxidant activity
and total polyphenol content, the tested tea types were ranked in the following order: white > green > black > red > other teas (yerba
mate > rooibos). Our experiment demonstrated a positive correlation between the polyphenol content and antioxidant activity of the
analyzed teas. Also, the DPPH antiradical efficiency was comparable to their ability to reduce ferric ions. The extended brewing time
had a significant effect on the antioxidant activity of the infusions and the polyphenolic compounds analyzed therein. In contrast,
storage of the infusions for 24 h at room temperature changed their antioxidant activity and affected the total polyphenol content.
Keywords: Tea infusion, FRAP, DPPH, polyphenols, flavonoids, brewing time
Please cite this article in press as: Kolodziej B, Sugier D, Luchowska K. Changes of antioxidant activity and active compounds
content in selected teas. Foods and Raw Materials. 2020;8(1):91–97. DOI: http://doi.org/10.21603/2308-4057-2020-1-91-97.
Copyright © 2020, Kolodziej et al. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International
License (http://creativecommons.org/licenses/by/4.0/), allowing third parties to copy and redistribute the material in any medium or format and to remix,
transform, and build upon the material for any purpose, even commercially, provided the original work is properly cited and states its license.
Foods and Raw Materials, 2020, vol. 8, no. 1
E-ISSN 2310-9599
ISSN 2308-4057
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Kolodziej B. et al. Foods and Raw Materials, 2020, vol. 8, no. 1, pp. 91–97
for the Polish market (Bastek Coffee & Tea, Mokate,
Unilever Polska, Teekanne Polska, Roger Sp. z o.o.,
Amber Spark, William’s Nature Products, Bio-active
Sp. z o.o., Herbapol-Lublin S. A., Posti S.A., Himalaje
– Najlepsze herbaty, Tata Global Beverages Polska
Sp. z o.o.) and purchased in retail stores. In particular,
we experimentally tested 5 white teas (W), 15 green teas
(G), 5 red teas (R), 15 black teas (B), and 5 other teas,
rooibos and yerba mate (Ro, YM). The names of the
teas were assigned digital (chosen randomly in the five
groups mentioned above) and letter designations.
Methodology of analyses. One gram of tea
was mixed with 100 mL of boiling distilled water,
covered, and brewed for 10 min. The extracts were
filtered through a medium-sized filter. The infusions
were assayed for the total polyphenol content
(o-dihydroxyphenols expressed as an equivalent of
caffeic acid) using the spectrophotometric method of
Singleton and Rossi and the flavonoid content (expressed
as an equivalent of quercetin) according to Polish
Pharmacopoeia VIII [13, 14].
Furthermore, we determined the antioxidant activity
of tea by using the FRAP method of Benzie and Strain
(the capacity of reducing 1 mole of Fe (III) to Fe (II)
expressed as μmoles of antioxidant compounds in 1 g of
raw material) and the modified DPPH Brand-Williams
et al. method using a free radical of 1,1-diphenyl-2-
picrylhydrazyl [15, 16]. The results were presented as %
of free radical scavenging.
Brewing time and freshness effects on antioxidant
activity and polyphenols. The samples under analysis
were brewed for 10 and 30 min and stored at room
temperature for 24 h. Next, we assessed their antioxidant
activity using the FRAP method and determined the
total polyphenol content. All assays for each sample
were performed in triplicate.
Statistical analysis. All the data were subjected to
variance analysis. The significance of the differences
between mean values were verified with Tukey’s test
(n = 3) at a significance level of 95%. Statistica 9.0
(StatSoft) program was employed for the calculations.
Additionally, we used Excel to calculate the coefficients
of simple correlations between the phytochemical
features of the infusions and their antioxidant properties.
RESULTS AND DISCUSSION
The analyzed samples of teas available on the Polish
market differed significantly in both the total polyphenol
and flavonoid contents and their antioxidant properties
evaluated after 10 min brewing (Table 1).
As we can see, the content of flavonoids in the
infusions assayed with the methodology provided in
FP VIII ranged from 0.06% for sample 12 BL (loose-leaf
black tea) to 0.53% for sample 26GL (loose-leaf green
tea) [14]. In general, the lowest values of the flavonoid
content were found for red teas (0.17–0.19%) and rooibos
(0.09–0.2%), whereas the average value in the other
Table 1 Polyphenols content, flavonoids content, FRAP
and DPPH antioxidant activity of tea after 10 min of brewing
Sample
number
Polyphenols
content
(caffeic acid
equivalent
mg g–1 dry
weight)
FRAP
antioxidant
activity
(equivalent
μmol FeSO4
g dm–1)
DPPH
antioxdant
activity
(%
scavenging
for 1g
dry matter)
Flavonoids
content, % g
dry matter-1
(calculated
as
quercetin)
1 BL 39.46 880.96 47.96 0.25
2 BL 83.40 982.64 91.76 0.47
3 BE 73.80 941.42 83.05 0.41
4 BL 71.40 930.43 68.63 0.42
5 BL 37.17 590.45 44.54 0.23
6 BL 81.08 578.28 66.53 0.49
7 BL 65.52 788.70 65.23 0.25
8 BL 57.56 645.41 60.49 0.28
9 BE 64.64 685.45 55.09 0.36
10 BE 75.72 515.12 3.76 0.08
11 BL 71.36 505.96 55.01 0.20
12 BL 32.16 461.53 72.54 0.06
13 BE 97.02 1035.66 57.15 0.39
14 BL 103.53 1317.66 66.01 0.44
15 BL 83.64 1148.91 53.39 0.21
Mean for B 69.17 800.57 59.41 0.30
16 GL 61.41 874.29 60.78 0.31
17 GL 121.50 1304.95 76.05 0.38
18 GE 114.32 1337.54 69.94 0.43
19 GL 78.69 1167.55 67.70 0.40
20 GE 85.60 1183.65 76.71 0.35
21 GE 107.03 899.82 37.38 0.24
22 GL 96.55 748.12 47.84 0.16
23 GL 86.67 379.59 24.35 0.30
24 GE 119.98 1033.55 30.12 0.14
25 GL 67.16 657.03 74.30 0.38
26 GL 126.35 2257.19 93.29 0.53
27 GE 94.55 1451.43 81.27 0.34
28 GL 126.04 1251.54 43.95 0.37
29 GL 114.23 1993.17 85.20 0.46
30 GL 107.69 1944.46 89.89 0.25
Mean for G 100.52 1232.26 63.92 0.34
31 WE 105.69 1388.97 79.16 0.35
32 WE 105.32 1300.64 70.92 0.40
33 WL 87.97 1311.89 64.42 0.23
34 WL 70.84 1400.81 61.26 0.19
35 WE 116.54 1630.40 81.27 0.36
Mean for W 97.27 1406.54 71.40 0.30
36 RE 38.99 676.42 52.24 0.17
37 RE 61.99 606.53 25.77 0.19
38 RL 42.85 707.69 25.34 0.18
39 RL 45.21 534.90 20.97 0.18
40 RL 46.29 622.39 29.08 0.18
Mean for R 47.07 629.59 30.68 0.18
41 RoE 45.81 723.54 54.88 0.14
42 RoE 29.06 603.01 29.62 0.09
43 YML 60.95 997.95 76.71 0.27
44 RoL 41.59 535.05 20.38 0.20
45 YML 75.19 895.75 46.15 0.26
Mean for RoY 50.52 751.06 45.55 0.19
LSD0.05 ** ** ** **
B – black tea; G – green tea; W – white tea; R – red tea; Ro – Rooibos tea;
YM – Yerba Mate, L – loose-leaf tea; E – bagged tea
***, **, * – significant at P ≤ 0.001, 0.01 or 0.05
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Kolodziej B. et al. Foods and Raw Materials, 2020, vol. 8, no. 1, pp. 91–97
types of tea was about 0.3%. The flavonoid content in
the analyzed teas highly correlated with their antioxidant
activity, determined with the FRAP and DPPH methods
(r2 = 0.548–0.666), and with the polyphenol content
(r2 = 0.582). These results were in agreement with those
reported by Castiglioni et al., as well as Fernando and
Soysa [17, 18].
The total polyphenol content determined with the
Folin-Ciocalteu method in the 45 analyzed tea infusions
ranged from 29.1 (sample 42 RoE – loose-leaf rooibos
tea) to 126.4 mg·mL–1 (sample 26 GL – loose-leaf green
tea), expressed as an equivalent of caffeic acid (Table 1,
Fig. 1). The values were comparable with those
reported by Hilal and Engelhardt [19]. The highest
content of polyphenols was found in the green teas
(average 100.5 mg·mL–1), just as in the experiments
described by McAlpine and Ward, Kiran and Kumar,
as well as Shannon et al. [20–22]. The white teas were
characterized by a slightly lower (mean 97.3 mg·mL–1)
content of the active compounds.
On average, the black teas contained 69.2 mg·mL–1
of polyphenols, whereas the red tea as well as rooibos
and yerba mate exhibited mean values of 47.1 and
50.5 mg·mL–1, respectively. Similar results were
reported by a number of researchers [7, 9, 21, 22].
However, Plust et al., as well as Hilal and Engelhardt,
found higher contents thereof in white teas and lower
contents in green teas and, especially, in black teas
[3, 19]. In our experiment, higher total contents of
polyphenols and flavonoids in green tea, compared
to white tea, might be due to slight oxidation of white
(nonfermented) tea polyphenols during production.
In fact, white teas do not undergo the inactivation of
enzymes before withering, so enzymes remain active
and white tea polyphenols are oxidized slowly [12].
The antioxidant activity (assessed with FRAP and
DPPH) and the polyphenol content demonstrated a
significant correlation (r2 = 0.435–0.732) and a considerable
diversity of the results. This correlation between
the results of the three tests confirmed the validity of the
procedure we used for analysis. However, Almajano et al.
found no linear correlation between the antiradical
activity of the analyzed infusions and the content of
polyphenolic compounds [9]. They suggested that
antiradical performance was influenced not only by
the content of polyphenols but also by their quality
and presence of other compounds that might enter the
infusions during extraction.
A slightly different relationship was discovered
by Rusaczonek et al. and Castiglioni et al., i.e. a linear
correlation between the total polyphenol content,
flavonoids content, and antioxidant properties measured
with ABST [7, 17]. Similar results were reported by
Plust et al., Molan et al. and Aldiab, who used the
FRAP method [3, 11, 23]. We should emphasize that the
available literature describes a variety of methods for
determination of antioxidant properties and polyphenolic
content of tea infusions. Also, the authors employ
different methods of extraction (temperature, time,
solvent) while preparing solutions for analyses and
express their results in different ways. Therefore, the
results are sometimes hardly comparable [1, 9, 11].
The antioxidant activity of the teas measured
with the FRAP method was in the range of 379.6–
2257.2 μmol g d.w.–1 The highest antioxidant activity was
exhibited by the white and green tea samples, while the
lowest activity was found for the red teas (over twice as
low). A similar trend was observed by Atalay and Erge
as well as Shannon et al. [12, 22].
On average, the black teas had 35% weaker
antioxidant properties than the green teas and a 43%
lower Fe ion reduction ability than the white teas. These
results were in line with the findings of Aldiab [23].
The antioxidant activity of this group of teas exhibited
a wide range of 461.5–1317.7 μmol g d.w.–1, which
indicated high variation of tea on the domestic market.
Figure 1 Changes in polyphenol content (caffeic acid equivalent mg·g–1 dry weight)
0
20
40
60
80
100
120
140
160
1BL
2BL
3BE
4BL
5BL
6BL
7BL
8BL
9BE
9BE
10BL
11BL
13BE
14BL
15BL
16GL
17GL
18GE
19GL
20GE
21GE
22GL
23GL
24GE
25GL
26GL
27GE
28GL
29GL
30GL
31WE
32WE
33WL
34WL
35WE
36RE
37RE
38RL
39RL
40RL
41RoE
42RoL
43YML
44RoL
45YML
caffeic acid equivalent mg g–1 dry weight
polyphenols content after 10 min of brewing polyphenols content after 30 min of brewing
polyphenols content after 24 h of infusion storing
0
500
1000
1500
2000
2500
1BL
2BL
3BE
4BL
5BL
6BL
7BL
8BL
9BE
9BE
10BL
11BL
13BE
14BL
15BL
16GL
17GL
18GE
19GL
20GE
21GE
22GL
23GL
24GE
25GL
26GL
27GE
28GL
29GL
30GL
31WE
32WE
33WL
34WL
35WE
36RE
37RE
38RL
39RL
40RL
41RoE
42RoL
43YML
44RoL
45YML
equivalent μmol FeSO4 g dm–1
FRAP after 10 min of brewing FRAP after 30 min of brewing FRAP after 24 h of infusion storing
С
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These teas had slightly weaker antioxidant properties
than green teas due to the oxidation of catechin
derivatives during processing and the presence of less
active theaflavins and thearubigins in the infusions [12].
The weaker antioxidant properties and a lower
polyphenol content in these tea types were confirmed by
other authors [12, 19]. Noteworthily, the loose-leaf white
and red teas were characterized by lower activity than
the bagged teas, while Plust et al. reported an opposite
trend for other tea types [3].
Generally, the analyzed red teas had a significantly
lower content of polyphenols and exhibited weaker
antioxidant activity. This result was probably due to the
differences in the manufacturing process, which involves
additional drying of tea leaves before they are twisted,
leading to slight fermentation of tea. Additional drying
may result in an increased loss of active substances.
Incomplete fermentation causes polymerization of
simple polyphenols, as in black teas, but it does not last
long. Another difference is the absence of heat treatment
for black tea, which may induce differences in the
composition of the pu-erh type teas.
DPPH is a stable free radical that antioxidants can
react with, providing it with electrons or hydrogen
atoms. As presented in Tables 1 and 2, the value of
antioxidant activity determined with the DPPH method
was closely related to the results obtained using the
FRAP method (r2 = 0.668).
Concurrently, there were substantial differences
in the antioxidant activity of the analyzed extracts
(from 3.8 to 93.3% radical scavenging). Just as in the
study of McAlpine and Ward, the lowest DPPH radical
scavenging percentage was found for red tea (20.9–
52.2%) and rooibos (20.4–54.9%), while the highest
values were reported for white (61.3–81.3%) and
green teas (24.4–93.3%) [21]. Similarly, Shannon et al.
confirmed a higher DPPH radical scavenging capacity of
green tea, followed by black tea [20].
The higher antioxidant activity of green tea
determined by both methods can be attributed to an
epigallocatechin gallate content, showing a greater free
radical scavenging capacity than the other catechins [12].
Our study found that the more processed the tea was,
the lower its antioxidant capacity. Similar results were
reported by Kiran and Kumar, as well as Cleverdon et al.
[21, 24]. However, they did not agree with the findings
of Fik and Zawiślak, possibly due to the application of
a different solvent during preparation of infusions and
differences in the geographical regions of tea cultivation,
harvesting periods, or storage conditions [8].
The most considerable differences between the
antioxidant activities of the analyzed extracts were
observed for the black teas. The loose-leaf types
exhibited higher activity than the bagged teas (Table 1).
Additionally, just as in Cleverdon et al., true teas had
at least a two-fold greater polyphenol content than the
herbal varieties [24]. The weaker free radical scavenging
capacity of rooibos tea (originating from Aspalathus
linearis L.) may result from its chemical composition:
unlike Camellia sinensis L., it does not contain catechins
but aspalathin, isoorientin, orientin, and rutin [24, 25].
Similarly, yerba mate (produced from Ilex
paraguariensis L.) does not contain catechins but
substantial amounts of chlorogenic acid [26]. We
found that the antioxidant activity of yerba mate was
substantially lower than that reported by Boji et al. [26].
However, as emphasized by Komes et al., yerba mate
can exhibit low antioxidant activity compared to white
and green teas [27].
It seems that the differences between the polyphenol
profiles of “true” and herbal or rooibos teas could be
the direct cause of the differences in their antioxidant
capacity found in our study. We should take into account
that the differences observed in these studies can be
related to different sample preparation methodologies
and use of different brewing times and tea-to-water
ratios. What is more, the comparison of results is
sometimes difficult due to the lack of uniformity in the
properties of green tea, manufacturing and brewing
conditions. Leaf age and size, harvesting season, and
manufacturing conditions are all important factors that
can affect the results [4].
Thus, according to our study, the teas tested with the
FRAP and DPPH methods exhibited antioxidant activity
in the following order: white teas > green > black > red
> other teas (yerba mate > rooibos).
In all the infusions, the total polyphenol content
increased (from 6.9% in red teas to 19.7% in black
teas) with the infusion time, with higher values noted
for bagged teas (Fig. 1). These findings are in line with
other studies conducted on different brands of loosely
packed and bagged teas. In particular, Armoskaite et al.
found that longer periods of extraction of green tea
(30 min) led to higher quantities of phenolic compounds
[2]. Nikniaz et al. reported similar results for black
teas [10]. However, storing infusions for 24 h at room
temperature had a varied effect on the content of these
active substances. Increased polyphenol contents were
detected in rooibos, yerba mate, red and white teas.
In our study, we found black and green tea samples
with increased polyphenol contents (1 BL, 2 BL, 4 BL,
5 BL, 7 BL, 8 BL, 12 BL, 13 BE, 14 BL, 15 BL and
Table 2 Single correlation coefficients between chosen
features of teas
FRAP 10 DPPH 10 FV 10
PL 10 0.732*** 0.435** 0.582***
FRAP 10 0.668*** 0.548***
DPPH 10 0.666***
PL 10 – polyphenols content after 10 min of brewing; FRAP 10 –
FRAP antioxidant activity after 10 min of brewing; DPPH 10 – DPPH
antioxidant activity after 10 min of brewing; FV 10 – flavonoids
content after 10 min of brewing
***, **, * – significant at P ≤ 0.001, 0.01 or 0.05
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Kolodziej B. et al. Foods and Raw Materials, 2020, vol. 8, no. 1, pp. 91–97
16 GL, 19 GL, 20 GE, 27 GE, 28 GL), while in the other
groups, the content declined from 4 to 42%. Similarly,
increased quercetin, flavonoids and total polyphenol
contents were recorded along with prolonged tea
brewing in Molan et al., Castiglioni et al., Fernando
and Soysa, as well as Palanivel et al. [11, 17, 18,
28]. According to Armoskaite et al., flavonoids (and
catechins, their fraction) are basic phenolic compounds
in green tea responsible for antioxidant activity [2].
What is more, Saklar et al. reported that green
tea catechins may be converted from epi forms to
non-epi forms due to epimerization reactions at long
brewing times [4]. Jin et al. proved that concentrations
of epicatechins peaked at 10 min, after which they
decreased drastically, while levels of non-epicatechins
increased steadily for 5 h [5]. However, the antioxidant
activity was more dependent on brewing temperature
than brewing time. It is worth emphasizing that tea
catechins can act as antioxidants by donating hydrogen
atoms or by chelating metals, but epicatechins are
known to be stronger than their corresponding non-epi
isomers [9].
Further, we assessed the Fe ion reduction ability of
the infusions brewed for 10 and 30 min (Fig. 2).
In the 45 teas analyzed, both a decline and an increase
in antioxidant activity (particularly in red teas and
yerba mate) were detected over the prolonged brewing
time. These results were in line with Nikniaz et al.
who reported higher values for bagged teas [10]. The
most substantial differences were found among the black
teas. In particular, infusions 1 BL, 2 BL, 3 BE, 4 BL,
and 5 BL exhibited a decreased Fe ion reduction ability
in a range of 4.2–26.6%, whereas the other infusions
were characterized by an increased ferric reducing
antioxidant power FRAP (from 1.4 to 44.5%). Increased
antioxidant activity was detected in the infusions of the
other tea types (except for green tea samples 23 GL,
25 GL, and 26 GL).
Previously published studies reported that the
antioxidant capacity and total polyphenols in tea
extracts correlated with the extraction time [10, 11, 19].
It is worth underlining that according to Armoskaite
et al. and Pastoriza et al., the time of extraction and
antioxidant activity may not always be in direct
proportion: longer extraction time results in lower
antioxidant activity in some green teas and higher in
others [2, 6].
In our study, the FRAP antioxidant activity of the
tea infusions stored for 24 h at room temperature varied
in a non-uniform manner and the statistical analysis
did not confirm the significance of the differences. The
magnitude of a decrease or an increase in antioxidant
activity was not correlated with the tea type: both were
noted in the groups of the same tea types. On average,
the black teas exhibited a 14.8% increase in the Fe ion
reduction ability. However, some infusions from this
group were characterized by a decreased Fe ion reduction
ability (samples 10 BE, 13 BE, 14 BL, and 15 BL).
In the other tea groups, we noted a decline in
antioxidant activity, particularly in the red and green
teas. At the same time, each group comprised some
samples with a Fe ion chelating ability that increased
throughout storage (samples 16 GL, 17 GL, 18 GE,
19 GL, 20 GE, 23GL of the green teas, samples 31 WL
and 32 WL of the white teas, sample 36 RE of the red
teas, and samples 41 RoE, 42 RoE, and 43 YML of the
teas other than Camellia sinensis). According to Komes
et al., this variation might be due to a great abundance
and variability of tea constituents that participate in
various reactions during storage in the presence of
oxygen, such as polymerization, or even degradation
of some tea compounds [30]. Therefore, as indicated
by Jayabalan et al., the qualitative and quantitative
composition of tea infusions undergoes change over time
with significant differences detectable only after several
days of brewing [29].
Figure 2 Changes in antioxidant activity of FRAP (Equivalent μmol FeSO4 g·dm–1) in the tested teas
0
20
40
60
80
100
120
140
160
1BL
2BL
3BE
4BL
5BL
6BL
7BL
8BL
9BE
9BE
10BL
11BL
13BE
14BL
15BL
16GL
17GL
18GE
19GL
20GE
21GE
22GL
23GL
24GE
25GL
26GL
27GE
28GL
29GL
30GL
31WE
32WE
33WL
34WL
35WE
36RE
37RE
38RL
39RL
40RL
41RoE
42RoL
43YML
44RoL
45YML
caffeic acid equivalent mg g–1 dry weight
polyphenols content after 10 min of brewing polyphenols content after 30 min of brewing
polyphenols content after 24 h of infusion storing
0
500
1000
1500
2000
2500
1BL
2BL
3BE
4BL
5BL
6BL
7BL
8BL
9BE
9BE
10BL
11BL
13BE
14BL
15BL
16GL
17GL
18GE
19GL
20GE
21GE
22GL
23GL
24GE
25GL
26GL
27GE
28GL
29GL
30GL
31WE
32WE
33WL
34WL
35WE
36RE
37RE
38RL
39RL
40RL
41RoE
42RoL
43YML
44RoL
45YML
equivalent μmol FeSO4 g dm–1
FRAP after 10 min of brewing FRAP after 30 min of brewing FRAP after 24 h of infusion storing
E
·
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Kolodziej B. et al. Foods and Raw Materials, 2020, vol. 8, no. 1, pp. 91–97
CONCLUSION
Our experiment demonstrated a considerable
diversity of teas available on the Polish market,
contributing to the variability of active compounds and
antioxidant activity of tea infusions. The teas under
analysis were characterized by varied free radical
scavenging abilities, and the amount of antioxidants
depended primarily on the type of tea. The nonfermented
teas (white and green) exhibited the highest
antioxidant activity (measured with the FRAP
and DPPH methods) and total polyphenol content.
Weaker antioxidant properties and a lower content of
polyphenols were detected in the black teas. The lowest
values were found in rooibos and yerba mate, as well as
in the red teas.
Our study showed a positive correlation between the
polyphenol content and antioxidant activity. In addition,
the DPPH antiradical performance of the examined
extracts was comparable to their Fe ion chelating
ability. The prolonged brewing time had a significant
effect on the antioxidant activity of the infusions and
polyphenolic compounds contained therein, which was
not a linear correlation. Similarly, storage for 24 h at
room temperature induced changes in the antioxidant
activity of the infusions and altered their total
polyphenol content.
The information contained in our study can be
useful for tea consumers in their choice of tea, as well
as preparation and storage methods that ensure the
best pro-health properties. In addition, the substantial
differences in the content of active compounds and
antioxidant properties of the examined tea types
manufactured by various producers suggest a need
for establishing appropriate technological parameters,
quality requirements, and systematic control of their
composition and properties. Given the fact that there
are no standards for teas other than black in Europe, the
quality of all types of tea traded on the Polish market
should be standardized to ensure similar quality of
products and fair market competition.
CONTRIBUTION
The authors were equally involved in writing the
manuscript and are equally responsible for plagiarism.
CONFLICT OF INTEREST
The authors declare that there is no conflict of
interest.

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