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Food Research 5 (3) : 107 - 111 (June 2021)
Journal homepage: http://www.myfoodresearch.com
Bioactive compounds and antioxidant activity of black and green tea available
in Bangladesh
1Rahman, M., 2Jahan, I.A., 3Ahmed, S., 2Ahmed, K.S., 1Roy, M., 1Zzaman, W. and
1,*Ahmad, I.
1Department of Food Engineering and Tea Technology, Shahjalal University of Science and Technology,
Sylhet-3114, Bangladesh
2Chemical Research Division, BCSIR Laboratories, Dhaka, Bangladesh Council of Scientific and Industrial
Research (BCSIR), Dhaka-1205, Bangladesh
3Department of Agro Product Processing Technology, Jashore University of Science and Technology,
Jashore-7408, Bangladesh
Article history:
Received: 6 September 2020
Received in revised form: 15
October 2020
Accepted: 30 November 2020
Available Online: 16 May
2021
Keywords:
Black tea,
Green tea,
Caffeine,
Bioactive compounds,
Antioxidant activity
DOI:
https://doi.org/10.26656/fr.2017.5(3).491
Abstract
People in Bangladesh are traditionally used to consume mainly black tea. However, some
tea manufacturing companies are now producing green tea, though in a small scale. To
create new knowledge as well as awareness about the consumption of green tea, the
present study was carried out to compare the black and green tea available in Bangladesh
based on their bioactive compounds and antioxidant activity. A total of eight brands of
black tea and two brands of green tea were bought from the supermarkets. Total phenolics,
total tannin, total flavonoids, and caffeine content were measured as bioactive compounds,
and antioxidant activity was evaluated by using two different methods such as DPPH (1,1-
diphenyl-2-picrylhydrazyl) radical-scavenging activity and ABTS+ radical scavenging
activity of methanol extracts of black and green tea. Every bioactive compound in black
and green tea was found to be significantly different (P < 0.05). The total phenolic
content, on average, was measured at 242.46 mg GAE/g dry extract and 763.41 mg GAE/
g dry extract in black and green tea, respectively. Black tea contained 6.47 mg TAE/g dry
extract tannin, whereas green tea had much more tannin content, 14.51 mg TAE/g dry
extract, which is more than double in amount. On the other hand, the total flavonoid
content was almost double in black tea (61.82 mg QE/g dry extract) compared to green tea
(31.85 mg QE/g dry extract). Antioxidant activities were determined at different
concentrations of tea samples. At every concentration, green tea presented higher ABTS+
and DPPH radical scavenging activity than black tea. The highest percentage of inhibition
was observed at 20 ppm both in black and green tea, finding 98.50 % and 99.07 %
inhibition, respectively. Overall, significantly (P < 0.05) higher amount of phenolic
compounds as well as antioxidant activity were observed in green tea.
1. Introduction
Tea, the most widely consumed beverage in the
world, is remarkable dietary sources of phenolic
antioxidants (Shannon et al., 2017). Tea is made
basically in three forms. In green tea preparation, the
oxidation of fresh leaf polyphenols is precluded. Black
tea is produced in such a way as to allow the oxidation
almost of all these substances, whereas Oolong tea
undergoes partial oxidation. However, teas are quite
different from herbal teas, also known as tisanes made
from spices, herbs, or other plant materials (Alexieva et
al., 2020). In tea leaves, three basic polyphenol groups
can be distinguished: catechin, theaflavins and
thearubigenes (Yanishlieva-Maslarova and Heinonen,
2001). As green tea skips the oxidation process, the same
biologically active components as in fresh leaves remain
intact in green tea, though - in various concentrations,
except for theaflavins and thearubigens that are mainly
abundant in black tea (Rahardiyan, 2019). Tea
polyphenols, particularly catechins in green tea, are not
only essential in plant physiology but also tremendously
beneficial to human health, acting as antioxidants, as
well as anti-inflammatory, anti-allergic,
antihypertensive, anticancer, and antimicrobial agents
108 Rahman et al. / Food Research 5 (3) (2021) 107 - 111
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(Lorenzo and Munekata, 2016; Rahardiyan, 2019). It is
evident that different types of teas work synergistically
to exhibit benefits to human health, also enhancing
consumer acceptance. Likewise, combining teas and
tisanes or medicinal drugs were found useful
(Malongane et al., 2017).
No other beverage is so popular as tea in
Bangladesh. The geographical location of Bangladesh
favors the tea climate. Traditionally people in
Bangladesh are used to drink black tea. Despite much
research on phenolic compounds of tea worldwide, little
is known about black and green tea available in
Bangladesh, necessitating the study on bioactive
compounds and antioxidant properties of both teas to
compare them, and eventually, that can act as strong
scientific evidence in making awareness about green tea
consumption in the country.
2. Materials and methods
2.1 Sample collection
Eight brands of black tea such as Ispahani, Taaza,
Seylon, Finlays, Kazi and Kazi, Fresh, National, and
Tetley and two brands of green tea such as Finlays and
Kazi and Kazi were collected from the local supermarket
at Sylhet.
2.2 Extraction of tea sample
Tea samples were extracted with methanol/water
(80:20, v/v) in a ratio of 3:1. The mixture of tea and
methanol was shaken for 48 h using an orbital shaker and
then filtered, and the procedure was repeated three times
for the maximum extraction. The methanol from the
filtrate was removed by a rotary evaporator (R-205,
Buchi, Switzerland). Finally, the filtrate was freeze dried
to obtain the solid extract for further analysis.
2.3 Determination of total flavonoids, tannins and
phenolics content
The aluminium chloride colorimetric method
described by (Chang et al., 2002) was used to estimate
the total flavonoid content in the tea extracts.
The tannins were determined using the Folin-
Ciocalteu Phenol reagent, as reported by (Amorim et al.,
2008).
The total phenolics content (TPC) was determined
using the modified Folin-Ciocalteu method (Wootton-
Beard et al., 2011).
2.4 Estimation of caffeine
Tea caffeine was determined using the method
described by Maidon et al. (2012).
2.5 DPPH and ABTS+ Radical s Scavenging Activity
Assay
The stable DPPH (1,1-diphenyl-2-picrylhydrazyl)
radical-scavenging activity was measured using the
modified method described by Shimada et al. (1992).
ABTS+ radical scavenging activity of tea extract was
determined according to the method described by
Baltrušaitytė et al. (2007) with slight modification.
2.6 Statistical Analysis
IBM SPSS Statistics software, version 20, was used
to analyze the data by one-way ANOVA, setting a
significant level at p<0.05. The mean values were
adapted by Duncan’s Multiple Range Test (DMRT)
(Duncan, 1955).
3. Results and discussion
Total Flavonoids, total Phenolic, total Tannin, and
caffeine content were analyzed to evaluate bioactive
compounds and two complementary methods viz. DPPH
(1,1-diphenyl-2-picrylhydrazyl) and ABTS+ radicals
scavenging activity assays were used to determine
antioxidant activity.
3.1 Bioactive compounds
Tea is well known for possessing a wide range of
bioactive compounds. In this research work, several
bioactive compounds were analyzed to compare the
black and green tea, which were summarized in Table 1
as well as in Table 2.
3.1.1 Total phenolic content
The range of total phenolic content of black tea was
found from 224.69 mg GAE/g dry extract to 254.62 mg
GAE/g dry extract. The phenolic content of green tea
was found 725.52 mg GAE/g dry extract, for Kazi and
Kazi and 801.31 mg GAE/g dry extract for Finlays. The
highest amount of phenolic content was determined in
Finlays green tea, whereas the lowest amount of phenolic
content was found in Taaza black tea. Phenolic content
in black and green tea varied significantly, and on
average, black and green tea contained 242.46 mg GAE/
g dry extract and 763.42 mg GAE/g dry extract,
respectively. (Craig, 1999) studied the health-promoting
properties of common herbs. He analyzed tea, including
others, and found an average total phenolic compound of
248 mg GAE/g dry extract in black tea and 776 mg
GAE/g dry extract in green tea. The main active
phenolics in green tea are catechins found in fresh
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leaves, such as epicatechin (EC), epicatechin gallate
(ECG), epigallocatechin (EGC) and epigallocatechin
gallate (EGCG), which partly undergo oxidation process
in black tea to form condensation products like
theaflavins, lowering the overall phenolic contents in
black tea (Peluso and Serafini, 2017).
3.1.2 Total tannin content
The total tannin content of black tea ranged from
6.37 mg TAE/g dry extract to 6.68 mg TAE/g dry
extract, whereas green tea contained 13.64 mg TAE/g
dry extract (Kazi and Kazi) and 15.39 mg TAE/g dry
extract (Finlays). In a study on the antioxidative action of
tea polyphenols, the average total tannin content was
found 7.59 mg TAE/g dry extract in black tea and 15.16
mg TAE/g dry extract in green tea (Hara, 2001).
According to another study (Hodgson and Croft, 2010),
total tannin content in black tea ranged from 5.5 to 7.50
mg TAE/g dry extract, and in green tea, it varied
between 12 to 15 mg TAE/g dry extract.
3.1.3 Flavonoid content
Total flavonoid content was plentiful in black tea,
ranged from 59.70 mg QE/g dry extract to 68.53 QE/g
dry extract, whilst a lesser amount was observed in green
tea: 33.27 QE/g dry extract for Kazi and Kazi and 30.43
QE/g dry extract for Finlays. Thus, a significant
difference was observed in the mean flavonoid content of
black and green tea, with 61.82 mg QE/g dry extract and
31.85 mg QE/g dry extract in black and green tea,
respectively.
3.1.4 Caffeine content
The caffeine content of black tea ranged from 30.65
ppm to 34.41 ppm, whereas green tea contained 21.30
ppm (Kazi and Kazi) and 27.30 ppm (Finlays). A
significantly higher amount (P<0.05) of caffeine was
observed in black tea (32.66 ppm) than that in green tea
(24.30 ppm). Chu and Juneja (1997) observed 20 to 35
ppm caffeine on a dry weight basis in green tea. In
another study, it was reported that black tea containd 30
to 50 ppm caffeine (Juliano and Griffiths, 2004).
3.2 Antioxidant activity
A compound is considered as an antioxidant only if
it can delay or inhibit the oxidation of a substrate by
forming a stable complex compound or in any other way
at a low concentration and antioxidant free radicals
generated after the neutralization should be stable
(Ahmed et al., 2020). Phenolic compounds having
radical scavenging capacity in tea mainly show
antioxidant activity. Free radicals play a deadly role in
the biological system, and the importance of antioxidants
is that they scavenge free radicals by donating electrons
or transferring hydrogen atom. There are several
methods of determination of antioxidant activity. Of
those, two methods like DPPH∙ and ABTS∙ radicals
scavenging assay were applied in the present study.
3.2.1 ABTS+ radical scavenging activity
In both assays (ABTS and DPPH free radicals), the
reduction of these radicals is estimated to determine the
scavenging capacity of a sample. Green tea was observed
to exert remarkably superior scavenging activity in both
Types of tea Brand of tea Total phenolic content
(mg GAE/g dry extract) Total tannin content
(mg TAE/g dry extract) Total flavonoid content
(mg QE/g dry extract) Caffeine content
(ppm)
Black Tea
Ispahani 254.55±2.14f 6.40±0.15a 63.60±1.23h 33.41±1.16f
Taaza 224.69±2.16a 6.40±0.20a 68.53±2.05j 34.15±1.51gh
Seylon 253.60±3.18e 6.68±0.18a 65.70±2.29c 30.74±2.08c
Finlays 254.62±4.08f 6.41±1.05a 64.44±2.10i 31.47±1.11d
Kazi & kazi 232.41±5.27c 6.37±1.13a 61.3±0.13g 32.60±2.11e
Fresh 230.67±3.28b 6.43±1.35a 59.70±1.12d 33.83±2.24g
National 254.57±4.15f 6.50±1.14a 60.77±1.19f 30.65±2.18c
Tetley 234.55±3.18d 6.60±1.16a 60.41±2.15e 34.41±1.16h
Green Tea Kazi & kazi 725.52±4.34g 13.64±1.33b 33.27±1.17b 21.30±2.16a
Finlays 801.31±6.12h 15.38±1.28c 30.42±1.42a 27.30±1.05b
Table 1. Bioactive compounds of black and green tea
Values are expressed as mean±SD (n=3), different letters in the same column denote significantly different at P<0.05
Types of Tea Total phenolic content
(mg GAE/g dry extract) Total tannin content
(mg TAE/g dry extract) Total flavonoid content
(mg QE/g dry extract) Caffeine content
(ppm)
Black 242.46±12.42a 6.47±1.19a 61.81±3.62b 32.63±1.47b
Green 763.42± 10.51b 14.51±1.99b 31.87±1.58a 24.36±3.28a
Table 2. Comparison of bioactive compound of black and green tea
Values are expressed as mean±SD (n=3), different letters in the same column denote significantly different at P<0.05
110 Rahman et al. / Food Research 5 (3) (2021) 107 - 111
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assays. Figure 1 represents that both black and green tea
showed more scavenging activity than the standard, and
green tea had more antioxidant activity than that of black
tea. At different concentrations, the percentage of
inhibition by green tea was significantly higher (P>0.05)
than that by black tea. The highest mean value of percent
inhibition for black tea was found at 98.50% at 20 ppm;
likewise, the highest inhibition (99.07%) in the case of
green tea was also determined at 20 ppm. The higher
TPC in green tea is the main reason to exhibit higher
scavenging activity because TPC and scavenging activity
is closely correlated (Erkan et al., 2008; Ahmed et al.,
2021). The present result is also comparable to other
findings (Oh et al., 2013), where green tea scavenged
more ABTS∙ radicals (187.36 mg AAE/g tea) than that
(118.53 mg AAE/g tea) of black tea.
3.2.2 DPPH radical scavenging activity
The two assays (DPPH and ABTS) respond
differently to antioxidants. DPPH is exclusively soluble
in organic media (providing limitation to determine
hydrophilic antioxidants); on the contrary, ABTS is
soluble in both organic and inorganic media, being
capable of estimating both hydrophilic and hydrophobic
antioxidants (Awika et al., 2003). Figure 2 illustrates that
green tea considerably performed more scavenging
activity, but black tea had lesser activity than that of
standard as well as green tea. At every concentration, the
variance of inhibition of black and green tea was found
significant. The highest inhibition for black tea was
found 86.70% at 80 ppm, while green tea inhibited most
(90.58%) at 100 ppm. The variation in composition, such
as phenolic compounds, of plant materials makes the
difference in scavenging free radicals. Green tea was
reported to have more scavenging effect than black tea in
several previous investigations (Oh et al., 2013; Peluso
and Serafini, 2017; Shannon et al., 2017).
4. Conclusion
Black and green tea of different brands were
compared with respect to bioactive compounds and
antioxidant activity. Green teas were found to have more
amounts of bioactive compounds except for flavonoid
and caffeine and subsequently showed much more
antioxidant activity than black teas. In addition, green tea
demonstrated significantly higher antioxidant activity
than standard ascorbic acid both in ABTS and DPPH
free radical scavenging assays. As the green tea
exhibited better antioxidant activity than the black tea,
this study will help to promote the consumption of green
tea in Bangladesh. It is also recommended for further
investigation on the feasibility survey on large scale
production of green tea in Bangladesh.
Conflict of interest
The authors declare no conflict of interest.
Acknowledgment
The authors thankfully acknowledge the Bangladesh
Council of Scientific and Industrial Research (BCSIR),
Dhaka-1205, Bangladesh, for laboratory support.
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