Antioxidative activity of tea polyphenol extracts in soybean oil

Vietnam J. Agri. Sci. 2016, Vol. 14, No. 7: 1060-1067 Tạp chí KH Nông nghiệp VN 2016, tập 14, số 7: 1060-1067 
www.vnua.edu.vn 
1060 
ANTIOXIDATIVE ACTIVITY OF TEA POLYPHENOL EXTRACTS IN SOYBEAN OIL 
Giang Trung Khoa
1*
, Bui Quang Thuat
2
, Ngo Xuan Manh
1
, Bui Thi Thanh Tien
1 
1
Faculty of Food Science and Technology, Vietnam National University of Agriculture 
2
Institute for Food Industry 
Email
*
: giangtrungkhoa@gmail.com 
Received date: 20.04.2016 Accepted date: 10.08.2016 
ABSTRACT 
Tea polyphenol extracts (TPE) (94.08% dry mater (DM) total polyphenols, 71.14% DM total catechins) at three 
concentrations (100 ppm, 200 ppm, and 400 ppm) were examined in soybean oil in accelerated oxidation conditions 
at 60
0
C. A sample without antioxidants and a sample with 100 ppm butylated hydroxyanisole (BHA) + 100 ppm 
butylated hydroxytoluene (BHT) were used as the negative and positive controls, respectively. The results showed 
that TPE was more effective than BHA+BHT for the stability of soybean oil at the same concentration (200 ppm). TPE 
was capable of the maintenance of the sensorial properties, and reductions of diene and peroxide formations as well 
as the secondary oxidative compounds (p-anisidine). Concerning the TPE concentration, 200 ppm of TPE was 
suitable to stabilize the soybean oil quality during storage. 
Keywords: tea polyphenol extract, antioxidative activity, soybean oil quality 
Hoạt tính kháng oxi hóa của polyphenol chè trong dầu đậu nành 
TÓM TẮT 
Chất chiết polyphenol chè (TPE) (hàm lượng polyphenol tổng số 94.08% chất khô (DM), catechin tổng số 
71.14% DM) ở 3 nồng độ (100 ppm, 200 ppm, và 400 ppm) đã được thử nghiệm trong dầu đậu nành trong điều kiện 
thúc đẩy oxi hóa ở 600C. Mẫu không bổ sung chất chống oxi hóa và mẫu được bổ sung 100 ppm butylated 
hydroxyanisole (BHA) + 100 ppm butylated hydroxytoluene (BHT) đã được sử dụng như các đối chứng negative và 
positive tương ứng. Kết quả chỉ ra rằng, TPE hiệu quả hơn hỗn hợp BHA+BHT đối với việc ổn định chất lượng dầu 
đậu nành ở cùng nồng độ (200 ppm). TPE có khả năng lưu giữ tốt các đặc tính cảm quan, làm giảm sự hình thành 
giá trị diene, peroxide cũng như các sản phẩm oxi hóa bậc 2 (p-anisidine) của dầu. Liên quan đến nồng độ xử lý 
TPE, 200 ppm là phù hợp để ổn định chất lượng của dầu đậu nành trong quá trình tàng trữ. 
Từ khóa: Chất chiết polyphenol chè, chất lượng dầu đậu nành, hoạt tính kháng oxi hóa. 
1. INTRODUCTION 
Tea, which is processed from tea leaves 
(Camellia sinensis L.), is the cheapest and the 
most popular beverage in the world. Many 
studies have shown that polyphenolic compounds 
extracted from green tea leaves are good 
antioxidants that have potentialities against 
many diseases, including cancers (Yang, 2006), 
obesity (Lin and Shoei-Yn, 2006), atherogenesis 
(Osada et al., 2001), and many others. 
The chemical composition of tea is complex: 
polyphenols, caffeine, amino acids, 
carbohydrates, protein, chlorophyll, volatile 
compounds, fluoride, minerals, and other 
undefined compounds (Graham, 1992). Among 
these, the main constituents belong to the 
polyphenol group accounting for 30% on a dry 
weight basis (Chang et al., 2000). Catechins 
(flavan-3-ols) are the principal composition of tea 
polyphenols and their major elements are: (+)-
catechin (C), (+)-gallocatechin (GC), (-) 
Giang Trung Khoa, Bui Quang Thuat, Ngo Xuan Manh, Bui Thi Thanh Tien 
1061 
epicatechin (EC), (-)-epicatechin gallate (ECG), 
(-)-epigallocatechin (EGC), and (-)-
epigallocatechin gallate (EGCG) (Graham, 1992) 
(Figure 1). These catechins are also considered to 
be responsible for the pharmaceutical properties 
of tea, including antioxidant and antibacterial 
activities (Mendel, 2007). 
During the last decades, many researchers 
have indicated that tea extracts/polyphenols can 
be used as a natural preservative in food 
matrices such as meats (McCarthy et al., 2001; 
Tang et al., 2001; Mitsumoto et al., 2005), fish 
(Lin and Lin, 2005; Seto et al., 2005), and 
vegetables (Martin-Diana et al., 2008). With 
regard to edible oil, Chen and Chan (1996) 
showed that a 200 ppm concentration of green 
tea catechins was more protective in terms of 
lipid oxidation than butylated hydroxytoluene 
(BHT) in canola oil heated at 95°C. In addition, 
Anna et al. (2006) evaluated the antioxidant 
activity of tea extracts against the oxidation 
(Rancimat test) of heated sunflower oil at 
1100C. At set interval times, samples were 
taken out to test for antioxidant activity. Their 
results indicated that the highest antioxidant 
activity was at 1000 ppm green tea ethanol 
extract, and was comparable to α-tocopherol 
activity. However, Malheiro et al. (2012) showed 
that the tea extract only protected olive oil from 
oxidation in the first 3 min under a microwave 
cooking condition. Later on, the extract was 
pro-antioxidant. 
In the oil industry, the addition of synthetic 
antioxidants, like butylated hydroxyanisole 
(BHA), BHT, and tertiary butylhydroquinone 
(TBHQ), to products has been a common 
practice over the years. However, the use of 
these types of antioxidants is controlled due to 
their toxic and carcinogenic potential (Chen at 
al., 1992; Sun and Fukuhara, 1997). The aim of 
this study is to investigate the protective effect 
of tea polyphenol extracts (TPE) as a natural 
antioxidant on the oxidative stability of soybean 
oils that are currently popular. 
Catechins Structure 
Figure 1. Chemical structures of major catechins found in tea (Yilmaz, 2006)
Antioxidative activity of tea polyphenol extracts in soybean oil 
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2. MATERIALS AND METHODS 
2.1. Materials 
2.1.1. Oil, tea polyphenols extract 
In this study, commercial extra virgin 
soybean oil without preservatives was 
purchased from Vinacommidities (Pho Noi, 
Hung Yen, Vietnam). 
The TPE was produced as follows: TPEs 
were extracted thre ... dding antioxidants 
(BHT, BHA, and TPE) to the oil at bday 0. The 
oil still maintained an original slightly yellow, 
specific odor, and clear state. 
Giang Trung Khoa, Bui Quang Thuat, Ngo Xuan Manh, Bui Thi Thanh Tien 
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 Table 1. Effect of TPE on the sensorial properties of soybean oil 
after 12 days of accelerated oxidation 
Formula Color Odor Clearness 
F1 Dark yellow Extremely rancidness Clearness, sans sediments 
F2 Dark yellow Rancidness Clearness, sans sediments 
F3 Yellow Slightly rancidness Clearness, sans sediments 
F4 Slightly yellow Sans curious odor Clearness, sans sediments 
F5 Slightly yellow Sans curious odor Clearness, slight sediments of TPE 
Note: F1 - without antioxidant, F2 - 100 ppm BHT + 100 ppm BHA, F3 - 100 ppm TPE, F4 -200 ppm TPE, 
F5 - 400 ppm TPE 
However, after 12 days of accelerated 
oxidation at a high temperature (600C), in two 
formulas (F1-without antioxidant and F2 - 
BHT+BHA), the oil color changed to dark 
yellow, and the odor was extremely rancid for 
F1 and a lower rancidity level for F2 
(BHT+BHA). In contrast, a slight rancidity 
appeared only for the treated oil with 100 ppm 
of TPE, and absolutely no rancidity occurrence 
in the treated oil samples at higher TPE 
concentrations (200 ppm and 400 ppm). In 
addition, these samples (F3, F4) maintained an 
original slight yellow color. However, there was 
a little TPE sediment in the formula which was 
introduced from 400 ppm of TPE. 
These results showed that the TPE limited 
sensorial modifications of the oil better than 
BHT and BHA during accelerated oxidation at a 
high temperature. However, it is necessary to 
obtain further observations such as the 
reduction of diene and peroxide formations. 
3.2. Effect of TPE on the free fatty acid 
content of soybean oil during accelerated 
oxidation 
The results of acidity values along the 
exposure time, with or without antioxidants, 
are presented in Table 2. There was not a 
remarkable change throughout the exposure 
time between control samples, the BHT+BHA 
sample and the added tea extracts samples. 
This fact could be explained by the nearly 
inexistence of water in the soybean oil. For this 
reason, under these conditions, hydrolysis is 
usually negligible. This result is in agreement 
with the research of Malheiro et al. (2012), in 
which tea extract was added to olive oil in 
microwave heating condition. 
Table 2. Effect of TPE on the free fat acids content 
of soybean oil during accelerated oxidation 
Formula 
Period of accelerated oxidation (days) 
0 3 6 12 
F1 0.467
Ab 
0.503
Aa 
0.500
Aa 
0.479
Ab 
F2 0.465
Ac 
0.483
Bb 
0.497
Aa 
0.487
Abc 
F3 0.463
Abc 
0.474
Cba 
0.483
Ba 
0.461
Bc 
F4 0.468
Aa 
0.469
Ca 
0.473
Ca 
0.464
Ba 
F5 0.467
Aa 
0.468
Ca 
0.470
Ca 
0.441
Cb 
Note: F1 - without antioxidant, F2 - 100 ppm BHT + 100 ppm BHA, F3 - 100 ppm TPE, F4 -200 ppm TPE, F5 - 400 ppm TPE. 
Means in a column (A-C across formulas) not having a common letter are different (p < 0.05). Means in the row (a-c across 
periods) not having a common letter are different (p < 0.05). 
Antioxidative activity of tea polyphenol extracts in soybean oil 
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Figure 2. Effect of TPE on the dienes value of soybean oil during accelerated oxidation 
Note: F1 - without antioxidant, F2 - 100 ppm BHT + 100 ppm BHA, F3 - 100 ppm TPE, F4 -200 ppm TPE, F5 - 400 ppm TPE. 
According to day, means with no common letters differ significantly (P < 0.05). 
However, at the same observation time, the 
values in the samples with added TPE were 
always lower than the control sample or the 
sample with added BHT+BHA (α = 0.05). It could 
be assured that the TPE is capable of limiting the 
hydrolysis of lipid seven at a high temperature. 
3.3. Effect of TPE on the diene value of 
soybean oil during accelerated oxidation 
The first stage in lipid peroxidation is an 
abstraction of hydrogen from a molecule of 
polyunsaturated fatty acid and formation of 
conjugated dienes. The diene value is used to 
verify the degree of oil oxidation, 
complementing the observations of the peroxide 
value. The results are presented in Figure 2. 
It is clear that the diene concentration in 
all samples increased according to the 
accelerated oxidation time, but it was very 
different between the formulas. The value of the 
negative control sample (from 7.8 AU/g oil to 
26.9 AU/g oil after 12 days) increased the 
highest compared to the sample with added 
BHA+BHT (20.1 AU/g after 12 days). The TPE 
exhibited an important protection effect against 
diene formation in the oil during the accelerated 
oxidation process, in particular at the 200 and 
400 ppm concentrations. At the 200 ppm and 
400 ppm TPE concentrations, after 12 days of 
accelerated oxidation, the diene concentration 
was only 30.9% and 41.3%, respectively, in 
comparison with these values in the control and 
BHA+BHT samples. Our results are similar to 
the research of Chen and Chan (1996) who 
indicated that green tea extract is more 
protective than BHT against lipid oxidation 
(oxygen consumption test) in canola oil under 
the same conditions. 
3.4. Effect of TPE on the peroxide value of 
soybean oil during accelerated oxidation 
Peroxide amounts are commonly used for 
an estimation of oxidative degradation. The 
results are presented in Figure 3. 
The results showed that before heat 
incubating, there did not exist a significant 
difference between the control sample (without 
antioxidant) and the added antioxidants 
samples (0.8 meq.O2/kg oil). However, 
throughout the exposure time, a strong increase 
in these values was observed for F1 and F2 
(control, BHA+BHT), whereas this change was 
very little within the added TPE samples, in 
particular the F4 and F5 formulas. Concretely, 
after 12 days of accelerated oxidation, the 
peroxide value varied from 0.8 meq.O2/kg oil to 
150.8 meq.O2/kg oil for the control (F1) and to 
123.7 meq.O2/kg oil for added oil BHA+BHT 
Giang Trung Khoa, Bui Quang Thuat, Ngo Xuan Manh, Bui Thi Thanh Tien 
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(F2), whereas this value was only to 11.7 
meq.O2/kg oil for the 200 ppm of TPE sample 
and 7.8 meq.O2/kg oil in the sample with 400 
ppm TPE added. In addition, we remarked that 
in general, the peroxide values of samples F4 
and F5 corresponded with the legal limit for 
vegetable oil after 12 days of exposure, a value 
of 10 meq.O2/kg oil (Commission Regulation 
(EC) No, 1989/2003). Similarly, the TPE 
inhibited peroxide formation in the oil during 
accelerated oxidation at a high temperature. 
These results are consistent with the research 
of Chen and Chan (1996) who indicated that 
green tea polyphenol extract containing 51.2% 
of EGCG, 18.7% of EGC, 11.8% of ECG, and 
12.3% of EC exhibited a significant protection to 
canola oil from lipid oxidation after 23 h of 
heating at 95°C. However, there was not a pro-
antioxidant activity of TPE as observed by 
Malheiro et al. (2012). 
Figure 3. Effect of TPE on the peroxide value of soybean oil during accelerated oxidation 
Note: F1 - without antioxidant, F2 - 100 ppm BHT + 100 ppm BHA, F3 - 100 ppm TPE, F4 -200 ppm TPE, F5 - 400 ppm TPE. 
According to day, means with no common letters differ significantly (P < 0.05). 
Figure 4. Effect of TPE on the para-anisidines value 
of soybean oil during accelerated oxidation 
Note: F1 - without antioxidant, F2 - 100 ppm BHT + 100 ppm BHA, F3 - 100 ppm TPE, F4 -200 ppm TPE, F5 - 400 ppm TPE. 
According to day, means with no common letters differ significantly (P < 0.05). 
Antioxidative activity of tea polyphenol extracts in soybean oil 
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3.5. Effect of TPE on the p-anisidine value of 
soybean oil during accelerated oxidation 
Similar to the TBARS test, the p-anisidine 
value is often used to determine a secondary 
lipid oxidation marker. The results of this 
determination are presented in Figure 4. 
Just as with the peroxides value, the p-
anisidines amount increased rapidlyafter just 3 
days of accelerated oxidation at 60°C for the 
control and the BHA+BHT samples. However, 
this value increased inconsiderably for samples 
with added TPE, especially for the samples with 
200 ppm and 400 ppm TPE. Concretely, after 12 
days of oxidation, the p-anisidine concentration 
increased from 2.5 AU/g to 25.8 AU/g oil in the 
control (F1) and to 14.8 AU/g in the BHA+BHT 
sample (F2), whereas it increased to only 3.9 
AU/g and 3.3 AU/g in the F4 and F5 samples, 
respectively. Similarly, the TPE was 
significantly effective in reducing secondary 
lipid oxidation in oil. 
4. CONCLUSIONS 
Tea polyphenols extracts containing 94.08% 
DM total polyphenols and 71.14% DM total 
catechins have strong antioxidative properties 
in lipid systems. Research showed that the TPE 
was more abundantly effective than BHA+BHT 
for the stability of soybean oil at the same 
concentration (200 ppm). TPE is capable of the 
maintenance of the sensorial properties, and of 
the reduction of diene and peroxide formations 
as well as the secondary oxidative compounds 
(p-anisidine). Concerning the TPE 
concentration, 200 ppm of TPE is suitable to 
stabilize soybean oil quality during storage. 
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