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Screening antioxidant activity of extracts from different tea samples,

Authors:
Mohammad Taheri
Mohammad Taheri
Mohammad Taheri
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Reyhaneh Sariri at Islamic Azad University, Lahijan Branch
Reyhaneh Sariri
Masoud Giahi at Islamic Azad University, Lahijan Branch
Masoud Giahi
Hossein Ghafouri at University of Guilan
Hossein Ghafouri
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Abstract and Figures

The antioxidant activity of water extracts from white, green and black tea was measured using three methods. The highest antioxidant activity was found to be related to white tea. Hot water extracts of green and normal black tea showed also statistically significant antioxidant activities (P < 0.05). There was no statistically significant difference between the antioxidant activities of black tea and tea wastes, i.e. barks and old leaves discarded in the factory. In conclusion, the antioxidant capacities of water extracts of green tea leaves were almost comparable to similar extracts obtained from white tea, i.e. very young tea leaves together with blossoms. It was concluded that, although white and green tea are excellent sources of antioxidants, still old tea leaves and barks which are often considered as agricultural and factory wastes, can also be used as potential source of natural antioxidants.
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Pharmacologyonline 2: 674-683 (2011) Taheri et al.
674
Screening antioxidant activity of extracts from different tea samples
Mohammad Taheri
1
, Reyhaneh Sariri
1*
Masoud Giahi
2
, and Hosein Ghafoori
1
1
Deparment of Biology, University if Guilan, Rasht, Iran
2
Department of Chemistry, Islamic Azad University Lahijan Branch, Lahijan, Iran
Summary
The antioxidant activity of water extracts from white, green and black tea was measured
using three methods. The highest antioxidant activity was found to be related to white tea.
Hot water extracts of green and normal black tea showed also statistically significant
antioxidant activities (P < 0.05). There was no statistically significant difference between
the antioxidant activities of black tea and tea wastes, i.e. barks and old leaves discarded in
the factory. In conclusion, the antioxidant capacities of water extracts of green tea leaves
were almost comparable to similar extracts obtained from white tea, i.e. very young tea
leaves together with blossoms. It was concluded that, although white and green tea are
excellent sources of antioxidants, still old tea leaves and barks which are often considered
as agricultural and factory wastes, can also be used as potential source of natural
antioxidants.
1. Introduction
Tea extracts are powerful antioxidants due to the presence of chemical compounds such
as epigallocatechin gallate (EGCG), epicatechin gallate (ECG), epigallocatechin (EGC)
and epicatechin (EC) as shown in Figure 1 (1). Most of these compounds act as effective
scavengers of free radicals (2). It has been shown that tea, the common drink world wide,
is able to reduce risk of coronary heart disease in aged men (3). Many research works
have focused on the natural antioxidants present in tea extracts. It has been reported that
ethanolic extracts of tea strongly inhibit oxidation of canola oil (4). Tea polyphenols are
considered to be responsible for the anticarcinogenic, antimutagenic and protection
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675
against cardiovascular diseases of tea (5). It has been shown that natural antioxidants in
tea possess stronger antioxidative activity than synthetic antioxidants such as butylated
hydroxyanisole, butylated hydroxytoluene and dl-α-tocopherol interestingly, tea
polyphenols are much less toxic than that of butylated hydroxyanisole, butylated
hydroxytoluene and dl-α-tocopherol (6). However, the composition of various chemical
compounds in tea may differ depending to growth conditions and region of production
(7).
Figure 1. Some important tea catechins.
Traditionally, both green and black tea is manufactured from young shoots, mainly the
first 2-4 leaves and a bud. However, old tea leaves and plant barks, are not commonly
used in tea manufacture and are usually discarded as waste. While green tea is found for
many years as a useful drink for health, the beautiful and aromatic tea blossoms are
recently considered as a drink. In this study, the water extracts of all types of tea were
compared for their antioxidant capacity.
2. Materials and methods
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Fresh green tea leaves and tea wastes (Camellia sinensis (L.) were collected from tea
lands in Lahijan (Northern Iran). The wastes were a mixture of old leaves comprised
leaves barks and stems, whereas green tea was considered as the first 2-4 leaves and a
bud. White tea was a Korean brand tea and purchased from a special supermarket in
Tehran. In order to inactivate polyphenol oxidase, all tea samples were soaked into
boiling water for 3 min. They were then drained, dried at room temperature and ground to
a fine powder. 2, 2-diphenyl-2-picrylhydrazyl hydrate (DPPH).
2,4,6-Tripyridyl-s-triazine
(TPTZ), sodium acetate, ferric chloride, gallic acid, Folin-Ciocalteu’s phenol reagent and
ferrous sulphate were purchased from Sigma representative in Iran. All solvents were of
reagent grade and obtained from Merck representative in Iran.
2.1. Preparation of methanolic extract from tea leaves
In a typical procedure, 10 g of the ground tea samples were boiled in 100 ml distilled
water on a magnetic hot plate for 2 hours. The initial extracts were then re-extracted with
60 ml of distilled water at a temperature from 100 to 130 °C for 30 minutes. The two
fractions were the cooled to room temperature, filtered and combined. The extracted
mixture was then dried 40 °C and weighed to determine the yield (8).
DPPH radical scavenging assay
This method is based on the reduction of stable DPPH
•
when it accepts a hydrogen from
an antioxidant compound. Radical scavenging activity of water extracts from white,
green, black and tea factory wastes against stable DPPH
°
was determined
spectrophotometrically. The changes in color (from deep-violet to light-yellow) were
measured at 515 nm using a UV/visible light spectrophotometer (Ultrospec 3000 from
Pharmacia Biotech).
Briefly, each dry extract (0.025 g) was added to 10 ml of hot water. A freshly prepared
solution of DPPH
°
in ethanol (6×10
−5
M) was always used for UV measurements. 3 ml of
Pharmacologyonline 2: 674-683 (2011) Taheri et al.
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ethanolic solution of DPPH
•
was then added to 77 µl extract solution in 1 cm path length
disposable microcuvettes and mixed. The final mass ratio of extracts with DPPH
°
was
approximately 3:1, 1.5:1, 0.75:1. The samples were kept in the dark for 15 min at room
temperature and then the decrease in absorption was measured. Absorption of blank
sample containing the same amount of ethanol and DPPH
•
solution was prepared and
measured daily. The experiment was carried out in triplicate. Radical scavenging activity
was calculated using the following relationship:
% Inhibition = [ (A
B
– A
A
) /A
B
] × 100
Where: A
B
-absorption of blank sample (t=0 min); A
A
-absorption of extract solution (t=15
min).
Total phenolic content by the Folin–Ciocalteu assay
The amount of total phenolic content (TPC) in aqueous tea extracts (100 °C, with
stirring) was determined according to the Folin-Ciocalteu procedure described in (9). In
short, an aliquot of 12.5 µl of water-soluble tea extract was mixed with 250 µl of 2%
sodium carbonate solution in 96-well microplates and allowed to react for 5 min at room
temperature. 12.5 µl of Folin-Ciocalteu phenol reagent (50%) was then added and
allowed to stand for 30 min at room temperature before the absorbance of the reaction
mixture was read at 650 nm using a plate reader. Calibration was achieved with an
aqueous gallic acid solution (100–1000 µg/ml). Total phenol values were expressed as
gallic acid equivalents (GAE) based on the calibration curve. The assay was carried out
in triplicate for duplicate extractions giving six observations for each sample. Values
given for each sample are means of six observations.
Evaluation of antioxidant activity using FRAP assay
The antioxidant activity (AOA) of water-soluble tea extracts (100 °C, with stirring) was
determined using the ferric reducing ability of plasma (FRAP) assay (10). The working
FRAP reagent was prepared by mixing 10 volumes of 300 mmol/l acetate buffer, pH 3.6,
with 1 volume of 10 mmol/l 2,4,6-tripyridyl-s-triazine (TPTZ) in 40 mmol/l hydrochloric
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678
acid and with 1 volume of 20 mmol/l ferric chloride. Freshly prepared FRAP reagent
(250 µl) was warmed to 37 °C for 10 min, followed by addition of 8.5 µl extract and
25 µl deionized water. Sample absorbance was then read at 595 nm after 30 min in a plate
reader.
A standard curve was prepared using different concentrations (1-12 mmol/l) of
FeSO
4
·7H
2
O. The results were corrected for dilution and expressed in mmol FeSO
4
/l. All
solutions were used on the day of preparation. All determinations were performed in
triplicate for duplicate extractions, giving six observations for each sample. Values for
each sample are means of six observations.
Statistical analysis
All determinations were carried out in three triplicate and data were subjected to analysis
of variance. Analysis of variance was performed using the ANOVA procedure. Statistical
analyses were performed according to the MSTATC software. Significant differences
between means were determined by Duncan’s multiple range tests. P values less than 0.05
were considered statistically significant.
Results and Discussion
The results obtained from DPPH assay are presented in Figure 1. The effect of
fermentation could be explained by comparing the antioxidant activity of black tea with
the two unfermented tea leaves, white and green. The wastes obtained from the tea
factory were other parts of the plant such as barks and stems which had been fermented
during the total fermentation process. Interestingly, these showed antioxidant activity
similar to black tea.
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679
0
10
20
30
40
50
60
70
80
90
100
White tea Green tea Black tea Tea wastes
Extracts
% Scavenging activity
against DPPH
Figure 1. The antioxidant power of water extracts of different tea samples measured by
DPPH assay. All values are means (±SD) of triplicate measurement for two separate runs
(n=6).
The results of total phenolic content, shown in Figure 2, are in agreement with the results
obtained by DPPH assay. It has been shown that many factors affect the extraction yield
including temperature and stirring during extraction on the FRAP and TPC values of
green tea. Based on the results of our literature survey, all extractions in this study were
performed at 100 °C with magnetic stirring (11). The higher antioxidant power for white
and green tea is expected as, it has been shown that fermented tea possesses significantly
lower reducing power than unfermented tea (12).
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680
0
5
10
15
20
25
30
35
40
White tea Green tea Black tea Tea wastes
Extracts
TPC (mg GAL/gdw)
Figure 2. Total phenol content (mg gallic acid equivalent GAE/gram dry weight) in hot
water extracts of different tea samples.
In Figure 3, the results obtained from another important antioxidant activity test are
compared in aqueous extracts of different tea types. It was found that all techniques used
in this research confirm that white tea contains the highest source of antioxidants.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
white.t ea green .t ea black.t ea waste.t ea
Ext racts
FRAP (mmol Fe/ml)
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681
Figure 3. Ferric reducing power (FRAP, mmol/ml) of water extracts from tea samples
measured by FRAP test.
The activity of this tea is almost comparable with galic acid, a well known effective
antioxidant. Table 1 has summarized the results, indicating that regardless of type of
assay used to measure the antioxidant power, white tea remained at the top. The other
interesting point emerged from this Table is that wastes obtained from the factory are
almost comparable to black tea in terms of antioxidant power. We have also examined
the antibacterial properties of aqueous tea extract (the results not show). It was found that
factory wastes could show antibacterial activity against both gram positive and gram
negative bacteria similar to black tea extracts. This part of investigation will be published
in due course. Studies have shown an overall positive relationship between FRAP and
TPC, but not among DPPH and TPC, or between DPPH and FRAP (13). We also found
that there is a statistically significant (P < 0.05) correlation between FRAP, DPPH and
TPC for fermented tea and for unfermented samples, white and green teas. It was found
that extracts from white and green tea had significantly higher (P < 0.05–0.0001) FRAP
and TPC values than fermented, black tea leaves. It has been reported by other
researchers that total phenolic content in different teas reduced with fermentation (14).
Table 1. A comparison between antioxidant activities of tea samples examined by
various techniques.
Tea sample FRAP (mmol Fe/ml) DPPH (%) TPC (mg/gDW)
White tea
Green tea
Black tea
Tea wastes
0.77
0.58
0.42
0.40
88.4
80.3
62.6
40.4
34.5
24.3
18.4
17.5
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682
Conclusions
The results obtained from this study demonstrated that a considerable variation is present
among both various tea samples determined by TPC as well as antioxidant properties
expressed by FRAP and DPPH. The antioxidant activity of tea increased significantly
(about two times) during various stages of fermentation when comparing white
(unfermented) to black tea and black tea wastes (fully fermented). Interestingly, tea
factory wastes showed antioxidant activity almost equal to that of black tea. Considering
the very low price of wastes, the comparatively clean conditions they are processed and
separated from the mail black tea and their significant antioxidant capacity, they could be
considered for used in pharmaceutical applications.
Acknowledgements
The authors express their sincere thanks to University of Guilan for financial support.
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... The assay was carried out according to literature with slight modifications [8][9][10]. The main principle is based on the ability of tea samples (DBT, ABT and NBT) to scavenge 2,2'-azino-bis (ethylbenzthiazoline-6-sulphonic acid or ABTS + ) radical cation. ...
... Total antioxidant activity was determined by the FRAP assay as per the standard operating procedure laid down by literature with slight modifications [8][9][10]. The procedure is based on the reduction of ferric to ferrous form in the presence of antioxidants in the black tea infusion. ...
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Full-text available
  • Jan 2017
The interest of consumers in food products that provide health benefits beyond standard nutrient requirements has increased globally. Green tea is rich in functional compounds referred to as catechins. There have been several studies on the major catechin monomers including epicatechin (EC), epigallocatechin (EGC), epigallocatechin gallate (EGCG), and epicatechin gallate (ECG) because of the many health benefits associated with the consumption of tea. Tea has been proved to contain significant levels of bioactive compounds such as catechins, which have demonstrated good antioxidant properties, but the problem with these compounds is instability during extraction and storage, which this study has addressed. In this study supercritical fluid extraction (SFE) method was used to solve the problem with solvent extraction and to improve extraction yield of the bioactive components of the tea leaves. Microencapsulation was used to enhance the stability of the extracted compounds during storage. Response surface methodology (RSM) was employed to design the experiment and to optimise the operating variables (pressure, temperature, and time) for the SFE extraction based on crude extract yield, total phenolic contents, and total catechin and epigallocatechin contents. The effects of pressure, temperature and time on the extraction yields were evaluated. The optimum extraction conditions for SFE were at a pressure of 30Mpa, temperature, 47.99oC and time of 40 minutes. Extraction yields obtained from the SFE were: crude at 6.65%, with total phenolic content of 28.07gGAE/100g, epigallocatechin gallate 44.11mg/g, and total catechin was 96.67mg/g. The extractable components of the solvent extracts were: crude yield in the range of 2.05 to 3.57%, total phenolic content between 11.43 and 22.43gGAE /100g, total catechin in the range of 45.22 to 79.33mg/g and epigallocatechin gallate from 22.55 to 38.55mg/g. These showed that the extractable components from the SFE were better than those obtained from standard solvent extraction. Microencapsulation by spray drying technology using three biopolymer materials; maltodextrin, gum arabic and chitosan was investigated. The spray-dried green tea extracts microparticles achieved encapsulation efficiency of between 71.41 and 88.08%. It was found out that the blend of maltodextrin /gum arabic /chitosan (25 :74:1) swelled most in simulated gastrointestinal fluid (SGF) whereas maltodextrin 100%. swelled most at the same time released most in simulated intestinal fluid (SIF) .The shelf-life study showed that catechins was best protected using gum arabic 100%, maltodextrin 100% whereas the blends of gum arabic: maltodextrin: chitosan (25:74:1) and maltodextrin: chitosan (99:1) showed better antioxidant properties when stored at 4oC with a half-life period in the range of 231 -288 weeks compared to half-life of 35 - 56 weeks and 41 -60 weeks at storage temperature of 40oc and 25oC respectively. The result of this study showed that microencapsulation substantially enhanced the stability of green tea extracts obtained from SFE. This study will serve as a useful reference for future applications of green tea extracts by functional food designers in the food industry.
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... The result of the antioxidant capacity obtained in this study for cold and hot tea extract by DPPH assay is presented in the table 1. The analysis of variance ANOVA showed significant differences between two extraction temperatures in the studied brands of green tea, in the following way: Oriental ® (D for cold tea extracts and G for hot tea extracts), Lipton ® (B for cold tea extracts and F for hot tea extracts), Hindú ® (CD for cold tea extracts and E for hot tea extracts), Jaibel ® (A for cold tea extracts and C for hot tea extracts), these results are similar to the study conducted by Taheri et al, (22), where they found that the antioxidant activity of tea increased significantly in hot extracts when comparing white and black tea and black tea wastes. Interestingly, tea factory wastes showed an antioxidant activity almost equal to that of black tea, these results can be explained because the water extraction of green tea at different temperatures varied in the yield of extracts and composition. ...
COMPARATIVE STUDY OF THE ANTIOXIDANT CAPACITY IN GREEN TEA BY EXTRACTION AT DIFFERENT TEMPERATURES OF FOUR BRANDS SOLD IN COLOMBIA ESTUDIO COMPARATIVO DE LA CAPACIDAD ANTIOXIDANTE EN TÉ VERDE POR EXTRACCIÓN A DIFERENTES TEMPERATURAS DE CUATRO MARCAS VENDIDAS EN COLOMBIA
Article
Full-text available
  • Sep 2017
Background: Tea (Camellia sinensis) is the most highly consumed beverage in the world in addition to water. The most common way of preparation is by immersing the tea bag in hot or cold water. In Colom-bia, it is a recent trend and the market is growing continuously. Objectives: The objective of this study is to compare the antioxidant characteristics of four brands of green tea sold in Colombia at room and hot-temperature in relation to the preparation conditions. Methods: Four commercial brands of green tea (Oriental ® , Lipton ® , Hindú ® , Jaibel ®) were used in an aqueous extraction at two temperatures: Cold tea extract (25°C) and hot tea extract (80°C). Total polyphenol concentration (TPC) was determined by Folin-Ciocalteu method; Total flavonoid content (TFC) was determined by spectrophotometric method and the antioxidant capacity was determined by two methods: DPPH radical capture assay, and the oxygen radical absorbance capacity (ORAC) assay. Finally, a method to quantify the catechins of the tea extracts, high performance liquid chromatography (HPLC) was applied. Results: The TPC vary between: 2.53-14.63 mg GAE/ g sample for cold tea extract and 29.34-55.06 mg GAE/g sample for hot tea extract. The TFC vary between: 2.67-7.08 mg CE/g per sample for the cold tea extract and 5.43-8.41 mg CE/ g sample for hot tea extract. A similar profile assays: for cold tea extract: 22.36-41.29 mg TE /g sample for DPPH and 22.95-46.25 mg TE/g sample for ORAC. Similarly, for hot tea extract the following ranges were: 38.50-110.01 mg TE/g sample for DPPH and 23.40-113.60 mg TE/g sample for ORAC. In general, the values obtained in each assay for each brand were as follows: Oriental ® > Lipton ® > Hindú ® > Jaibel ®. The chromatographic profiles showed the presence of ten compounds. Conclusions: These results confirm that the aqueous extraction of green tea at 80°C leads to the formation of infusions made up of compounds with higher antioxidant capacity in comparison with extractions at room temperature.
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... The result of the antioxidant capacity obtained in this study for cold and hot tea extract by DPPH assay is presented in the table 1. The analysis of variance ANOVA showed significant differences between two extraction temperatures in the studied brands of green tea, in the following way: Oriental ® (D for cold tea extracts and G for hot tea extracts), Lipton ® (B for cold tea extracts and F for hot tea extracts), Hindú ® (CD for cold tea extracts and E for hot tea extracts), Jaibel ® (A for cold tea extracts and C for hot tea extracts), these results are similar to the study conducted by Taheri et al, (22), where they found that the antioxidant activity of tea increased significantly in hot extracts when comparing white and black tea and black tea wastes. Interestingly, tea factory wastes showed an antioxidant activity almost equal to that of black tea, these results can be explained because the water extraction of green tea at different temperatures varied in the yield of extracts and composition. ...
COMPARATIVE STUDY OF THE ANTIOXIDANT CAPACITY IN GREEN TEA BY EXTRACTION AT DIFFERENT TEMPERATURES OF FOUR BRANDS SOLD IN COLOMBIA ESTUDIO COMPARATIVO DE LA CAPACIDAD ANTIOXIDANTE EN TÉ VERDE POR EXTRACCIÓN A DIFERENTES TEMPERATURAS DE CUATRO MARCAS VENDIDAS EN COLOMBIA
Article
Full-text available
  • Nov 2017
Background: Tea (Camellia sinensis) is the most highly consumed beverage in the world in addition to water. The most common way of preparation is by immersing the tea bag in hot or cold water. In Colombia, it is a recent trend and the market is growing continuously. Objectives: The objective of this study is to compare the antioxidant characteristics of four brands of green tea sold in Colombia at room and hot-temperature in relation to the preparation conditions. Methods: Four commercial brands of green tea (Oriental®, Lipton®, Hindú®, Jaibel®) were used in an aqueous extraction at two temperatures: Cold tea extract (25°C) and hot tea extract (80°C). Total polyphenol concentration (TPC) was determined by Folin-Ciocalteu method; Total flavonoid content (TFC) was determined by spectrophotometric method and the antioxidant capacity was determined by two methods: DPPH radical capture assay, and the oxygen radical absorbance capacity (ORAC) assay. Finally, a method to quantify the catechins of the tea extracts, high performance liquid chromatography (HPLC) was applied. Results: The TPC vary between: 2.53-14.63 mg GAE/ g sample for cold tea extract and 29.34-55.06mg GAE/g sample for hot tea extract. The TFC vary between: 2.67-7.08mg CE/g per sample for the cold tea extract and 5.43-8.41 mg CE/ g sample for hot tea extract. A similar profile assays: for cold tea extract: 22.36 - 41.29 mg TE /g sample for DPPH and 22.95-46.25mg TE/g sample for ORAC. Similarly, for hot tea extract the following ranges were: 38.50 - 110.01 mg TE/g sample for DPPH and 23.40- 113.60 mg TE/g sample for ORAC. In general, the values obtained in each assay for each brand were as follows: Oriental®> Lipton®> Hindú®> Jaibel®. The chromatographic profiles showed the presence of ten compounds. Conclusions: These results confirm that the aqueous extraction of green tea at 80°C leads to the formation of infusions made up of compounds with higher antioxidant capacity in comparison with extractions at room temperature.
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YEŞİL ÇAY FABRİKA ATIKLARINDAN FARKLI YÖNTEMLERLE ANTİOKSİDAN BİLEŞİKLERİN EKSTRAKSİYONU
Thesis
Full-text available
  • Jul 2016
Bu çalışmada, yeşil çay fabrika atıklarından antioksidan bileşiklerin klasik (KE), ultrason (UDE) ve mikrodalga destekli ekstraksiyon (MDE) yöntemlerinin ekstraksiyon koşulları, yanıt yüzey yöntemi ve Box-Behnken tasarımı kullanılarak faktörler ve yanıtlara göre optimize edilmiştir. Faktörler, KE ve UDE için; sıcaklık (20-60 °C), süre (15-45 dakika) ve etanol konsantrasyonu (% 40-60), MDE için; güç (300-600 Watt), süre (2-6 dakika) ve etanol konsantrasyonu (% 40-60) olarak seçilmiştir. İstenilirlik fonksiyonuna göre optimum ekstraksiyon koşulları KE için; 51.51 °C, 39.34 dakika, % 62.63 etanol konsantrasyonu, UDE için; 44.96 °C, 45 dakika, % 66.7 etanol konsantrasyonu ve MDE için; 599.39 Watt, 4.21 dakika, % 79.54 etanol konsantrasyonu olarak belirlenmiştir. Belirlenen optimum koşullarda elde edilen tahminsel ve deneysel toplam fenolik madde (TFM), FRAP ve EC50 değerleri sırası ile KE için; 22.75 mg GAE/g, 592.97 mmol/g, 8.90 μg/mL; 38.20±0.29 mg GAE/g, 585.61±24.16 mmol/g ve 10.42 ±0.29 μg/mL, UDE için; 25.47 mg GAE/g, 594.61 mmol/g, 12.29 μg/mL; 33.14±0.45 mg GAE/g, 377.37±27.31 mmol/g ve 10.28±0.81 μg/mL ve MDE için; 623.26 mmol/g, 9.95 μg/mL; 40.72±0.85 mg GAE/g, 529.44±22.07 mmol/g ve 8.56±0.11 μg/mL’dir. Optimum koşullarda HPLC ile belirlenen kafein, GA, C, EC, ECG, EGC ve EGCG oranları sırası ile KE için; % 2, 0.35, 0.78, 0.02, 1, 0.27 ve 6.15, UDE için; % 1.69, 0.51, 0.54, 0.03, 0.82, 0.01 ve 5.81 ve MDE için; % 2.06, 0.2, 0.51, 0.03, 0.93, 0.05 ve 6.3’tür. Tüm yanıtlar üzerinde etkili faktörler; KE’da sıcaklık, UDE’da sıcaklık ve etanol konsantrasyonu ve MDE’da güç ve etanol konsantrasyonu olarak bulunmuştur. Antioksidan aktivite, bireysel kateşin verimi ve süre açısından bakıldığında MDE yönteminin KE ve UDE yöntemlerine göre daha üstün olduğu bulunmuştur.
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Influence of region of production on clonal black tea chemical characteristics
Article
Full-text available
  • May 2008
  • FOOD CHEM
Production of black tea from the same vegetatively propagated (VP) cultivars, in Kenya and Malawi, shows variations in both chemical composition and quality. Whereas it is possible to produce black teas with similar total theaflavins and individual theaflavins, brightness and total colour levels, black teas from Kenya generally have higher thearubigins, total volatile flavour compounds and flavour index. The black tea fermentation process is much faster in Malawi compared to that in Kenya, as evidenced by faster production of plain black tea chemical parameters, especially theaflavins. Consequently, in Malawi the maximum amount of theaflavins formation takes a shorter fermentation duration than in Kenya. Given ample fermentation duration, fermentation in Kenya produces a similar amount of theaflavins. This makes it necessary to optimise fermentation time, in different geographical regions even when the same cultivar is being processed. The other plain black tea quality parameters (thearubigins, brightness and total colour) were higher in black tea which was processed in Kenya than those processed in Malawi. However, the pattern in the changes in the individual theaflavins or theaflavins digallate equivalent followed that of total (Flavognost) theaflavins, suggesting that the flavan-3-ols patterns in tea leaf might not have been affected by the geographical area of production. The total volatile flavour compounds (VFC), Group I and II VFC and the flavour index were higher in black teas processed in Kenya, further demonstrating the fact that high grown Kenyan teas are more flavoury. In both Kenya and Malawi black teas, aroma quality declined with a long duration of fermentation. Short fermentation time is therefore a method of producing more aromatic black teas. The variations in black tea quality between Malawi and Kenya were possibly due to difference in environmental conditions, leading to different shoot growth rates and biochemical composition in the shoots.
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Antioxidative effect of ethanol tea extracts on oxidation of canola oil
Article
  • Mar 1996
There is an increasing interest in the biological effects of natural antioxidants present in teas on formation ofin vivo free radicals, carcinogenesis, and atherogenesis. Teas are traditionally classified into six major groups, namely, green, yellow, white, black, dark-green, and oolong teas. The present study examined the antioxidative activity of ethanol extracts from these six major groups of teas against oxidation of heated canola oil. The oxidation was conducted at 100°C by monitoring oxygen consumption and changes in linoleic and linolenic acids in canola oil. The ethanol extracts of green, yellow, and white teas strongly inhibited oxidation of canola oil compared to butylated hydroxytoluene, probably due to the presence of natural polyphenols. In contrast, oolong teas examined exhibited only moderate antioxidative activity because of the partial destruction of natural polyphenols by semifermentation. The ethanol extracts of black, dark-green, and ginseng teas studied showed little or no protection to canola oil from lipid oxidation, probably due to the complete destruction of natural polyphenols by fermentation during manufacturing processes.
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Selenium-containing green tea has higher antioxidant and prebiotic activites than regular green tea
Article
  • Jun 2009
  • FOOD CHEM
The effects of selenium-containing green tea (SGT: 1.4 mg selenium/kg) and China green tea (CGT: 0.13 mg selenium/kg) on the in vitro growth of lactobacilli and bifidobacteria were investigated using pure and mixed cultures. SGT had significantly higher phenolic contents (TPC), higher reducing activity, higher DPPH free-radical scavenging activity, and higher ferrous-ion chelating activity (P < 0.05-0.0001) than CGT. The addition of aqueous extracts from CGT to Mann-Rogosa-Sharpe (MRS) broth at 10% and 25% (v/v) resulted in small but nonsignificant (P > 0.05) increases in the numbers of Lactobacillus rhamnosus and Bifidobacterium breve over the control incubations (without tea). Addition of 10% and 25% of SGT extract resulted in a significant increase (P < 0.05-0.0001) in the number of lactobacilli and bifidobacteria recovered from batch fermentation while CGT did not increase the number of bifidobacteria. The higher prebiotic activity of SGT over CGT may be related to the higher TPC or minerals, notably selenium or a combination of these factors. To test whether selenium itself has an effect on bacterial growth, Na-selenite and Na-selenate were added alone or in combination with CGT to the MRS broth containing pure culture of L rhamnosus. Growth of this bacterium was enhanced relative to the control incubation of MRS only. When added in combination with CGT, Na-selenate was more effective at enhancing the growth of L rhamnosus than Na-selenite. The prebiotic effect of SGT could be largely explained by its selenium content.
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Polyphenolic Flavanols as Scavengers of Aqueous Phase Radicals and as Chain-Breaking Antioxidants
Article
  • Oct 1995
The purpose of this investigation was to establish the relative antioxidant activities in vitro of the flavanolic polyphenols, the catechins, and catechin-gallate esters. The relative antioxidant potentials were measured against radicals generated in the aqueous phase and against propagating lipid peroxyl radicals. The results show that in the aqueous phase their order of effectiveness as radical scavengers is epicatechin gallate (ECG) > epigallocatechin gallate (EGCG) > epigallocatechin (EGC) > gallic acid (GA) > epicatechin congruent to catechin; against propagating lipid peroxyl radical species, epicatechin and catechin are as effective as ECG and EGCG, the least efficacious being EGC and GA. This is consistent with their relative abilities to protect against consumption of LDL alpha-tocopherol. The results are discussed in the context of the most relevant antioxidant constituents of green tea extracts.
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The Ferric Reducing Ability of Plasma (FRAP) as a measure of “antioxidant power”: The FRAP assay
Article
  • Jul 1996
A simple, automated test measuring the ferric reducing ability of plasma, the FRAP assay, is presented as a novel method for assessing "antioxidant power." Ferric to ferrous ion reduction at low pH causes a colored ferrous-tripyridyltriazine complex to form. FRAP values are obtained by comparing the absorbance change at 593 nm in test reaction mixtures with those containing ferrous ions in known concentration. Absorbance changes are linear over a wide concentration range with antioxidant mixtures, including plasma, and with solutions containing one antioxidant in purified form. There is no apparent interaction between antioxidants. Measured stoichiometric factors of Trolox, alpha-tocopherol, ascorbic acid, and uric acid are all 2.0; that of bilirubin is 4.0. Activity of albumin is very low. Within- and between-run CVs are <1.0 and <3.0%, respectively, at 100-1000 micromol/liter. FRAP values of fresh plasma of healthy Chinese adults: 612-1634 micromol/liter (mean, 1017; SD, 206; n = 141). The FRAP assay is inexpensive, reagents are simple to prepare, results are highly reproducible, and the procedure is straightforward and speedy. The FRAP assay offers a putative index of antioxidant, or reducing, potential of biological fluids within the technological reach of every laboratory and researcher interested in oxidative stress and its effects.
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Total Phenol, Catechin, and Caffeine Contents of Teas Commonly Consumed in the United Kingdom
Article
  • Jan 2002
Levels of total phenol, catechins, and caffeine in teas commonly consumed in the United Kingdom have been determined using reversed phase high-performance liquid chromatography. Tea bags or tea leaves were purchased from local supermarkets and extracted in boiling water for 5 min. The resulting data showed considerable variability in both total phenols [80.5-134.9 mg/g of dry matter (DM) in black teas and 87-106.2 mg/g of DM in green teas] and catechins (5.6-47.5, 51.5-84.3, and 8.5-13.9 mg/g of DM in black, green, and fruit teas, respectively); this was most probably a result of differing agronomic conditions, leaf age, and storage during and after transport, as well as the degree of fermentation. Caffeine contents of black teas (22-28 mg/g of DM) were significantly higher than in less fermented green teas (11-20 mg/g of DM). The relative concentration of the five major tea catechins ranked EGCG > ECG > EC > EGC > C. The estimated U.K. dietary intakes of total tea catechins, calculated on the basis of an average tea consumption of three cups of tea (200 mL cup, 1% tea leaves w/v), were 61.5, 92.7, and 405.5 mg/day from fruit teas, black teas, and green teas, respectively. The coefficients of variation were 19.4, 88.6, and 17.3%, respectively, indicating the wide variation in these intakes. The calculated caffeine intake ranged between 92 and 146 mg/day. In addition, many individuals will consume much larger quantities of tea, of various strengths (as determined by the brewing conditions employed). This broad spread of U.K. daily intakes further emphasizes the need for additional research to relate intake and effect in various population groups.
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Comparison of the antioxidant activity of roasted tea with green, oolong, and black teas
Article
  • Jan 2006
Although the antioxidant properties of green, oolong, and black teas have been well studied, antioxidant activity has not been examined in roasted tea. Therefore, in the current studies, we investigated the antioxidant activity of roasted tea in comparison with those of green, oolong, and black teas. Using water extracts of the various teas, we examined the total phenolic content as well as the antioxidant activities, including the reducing power, the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, and the inhibition of hemolysis caused by 2,2'-azo-bis(2-amidinopropane) dihydrochloride (AAPH)-induced lipid oxidation in erythrocyte membranes. The roasted tea contained lower levels of total phenolics than green, oolong, or black tea (green tea > oolong tea > black tea > roasted tea). The relative reducing power and DPPH scavenging activity decreased in the following order: green tea > roasted tea > oolong tea > black tea. Also, green tea was more effective against AAPH-induced erythrocyte hemolysis than other teas (green tea>roasted tea = oolong tea = black tea). These results suggest that roasted tea is beneficial to health, in humans, because of its high antioxidant activity.
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