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The effect of brewing conditions on the rate of extraction of phenolic compound from tea residue and tea product has been determined. The results showed that total phenolic compounds increased with brewing time (0.5-75 min) and temperature (70, 80, and 90oC). Increasing of these compounds during brewing followed first-order reaction and conformed to Arrenius equation. The activation energy of polyphenol extraction from tea residue and tea product was 20.1 and 19.1 kJ/mol, respectively.
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Kinetics Studies of Total Phenolic Compounds During Brewing Condition of Tea
Residue and Tea Product

P. Ekwongsupasarna,*, S. Siriwattanayotina, W. Ruenglertpanyakulb and P. Suthamwonga,c

aDepartment of Food Engineering,
bDepartment of Chemical Engineering
Faculty of Engineering, King Mongkut’s University of Technology Thonburi, Bangkok
10140

Abstract
The effect of brewing conditions on the rate of extraction of phenolic compound from tea
residue and tea product has been determined. The results showed that total phenolic
compounds increased with brewing time (0.5-75 min) and temperature (70, 80, and 90oC).
Increasing of these compounds during brewing followed first-order reaction and
conformed to Arrenius equation. The activation energy of polyphenol extraction from tea
residue and tea product was 20.1 and 19.1 kJ/mol, respectively.

Keywords: Tea residue; Total phenolic compounds; Brewing; Kinetic rate; Extraction

1. Introduction

Northern of Thailand is the main tea crop area. Especially at Doi Mae Salong in Chiang
Rai; the biggest tea producer of Thailand produces approximately 5,100 tons monthly [1].
The process of commercial Oolong tea involves 7 stages which are freshly leaves
plucking, outdoor withering, indoor withering, firing, rolling, mass breaking, and drying.
During rolling and mass breaking step, 3 to 5 percent of tea product becomes residue. This
huge amount of residue is found to be very attractive due to its richness in polyphenol
compound.

Phenolic compounds or tea polyphenols make up 25-35% of the dry matter content of
young, fresh tea leaves. The major constituents of phenolics compounds are flavonoids
which possess strong antioxidant. The beneficial effects of tea have been documented in
various scientific records. drinking tea is good for health because polyphenols in tea may
reduce the rate of cancer and heart disease [2]. Tea polyphenol were also found to inhibit
bacterial mutation, HIV reverse transcriptase activity [3], as well as to degenerate diseases
of aging, such as cancer, cardiovascular disease, cataracts, immune system decline, and
brain dysfunction [4]. The considerable antioxidant potential of tea has long recognized
and was found to depend on many factors involved in tea preparation.

It is necessary to investigate the feasibility to utilize the residue as health care product,
total phenolic beverage. The objective of this work was to investigate the effect of
brewing condition on the amount of extracted total phenolic compounds of tea residue and
tea product.




_______________________________________________________________________________________
cCorresponding author. Tel.: +662 4709244-45; fax: +664702940. E-mail address:
pstong@hotmail.com (P. Suthamwong)

2. Materials and Methods

2.1 Materials and chemicals
Tea residues and tea product (Oolong no.12) used in this work was obtained from Doi
Tung Top Tea Cooperative, Maefahlaung, Chiang Rai. Tea residue were packed into a
vacuum plastic bag and stored at room temperature to reduce the effect of aging. Folin–
Ciocalteu reagent Gallic acid and sodium carbonate were of analytical grade.

2.2 Tea brewing
Water extract of Tea residues and tea product was obtained as follows. In brief, 2 g of tea
residue and tea product were brewing with 100 volumes of distilled water with shaking at
70, 80, and 90 oC for 0.5-75 min. The extracts were filtered through a filter paper and cool
at room temperature. All treatment was performed in three replications.

2.3 Determination of total phenolic content
Volume of 0.5 ml of distilled water and 0.125 ml of a known dilution of the extract were
added to a test tube, followed by addition of 0.125 ml of Folin-Ciocalteu reagent. They
were mixed well and then allowed to stand 6 min before 1.25 ml of a 7% sodium
carbonate solution was added. The mixture was diluted to 3 ml with distilled water. The
colour was developed for 90 min at room temperature and the absorbance was measured at
760 nm using a spectrophotometer. The measurement was compared to a standard curve
of prepared gallic acid solutions and expressed as means (±SD) mg of gallic acid
equivalents per gram for the triplicate extracts [5].

3. Results and Discussion
3.1 Effects of Temperature and Brewing Time on Total Phenolics Content of Tea Infusion
The total phenolic compounds of tea product and tea residue at different brewing time has
shown in Figure 1. The data show that total phenolic compounds increase with time and
temperature increasing. The %GAE rises rapidly in the first ten minutes, and then
approached a limiting equilibrium concentration (C∞) within 45 minutes. Temperatures
were not clearly effecting on %GAE for tea residue and at 80 and 90oC for tea product. %
GAE of tea residue brewing between 15 to 75 min and between 45 to 90 min for tea
product were not significantly different. The final observed %GAE were used as C

3.2 Extraction kinetics studies
Using linear regreassion, the data was analyzed using Eq. (1) referring to Spiro’s steady
state kinetic model [6] which assumed the first order behavior. The values of C∞ and k, at
different time were estimated. The kobs values, the observed first order rate constant, were
obtained from the slope of the semilog graph (Figure 2 and 3) and a from the intercept
values. The theory suggested that the line should pass through the origin, however (Figure
2 and 3) non-zero intercepts were found. This was also reported in other works, such as in
determination of caffeine extraction rate [8] that the intercept was the result of a complex
infusion process. They affirmed that the intercept is affected by the loss of soluble, the leaf
structure and its uptake of water at the beginning of infusion process. The data at 80 and
90oC fit well into Eq. (1) as seen in Figure 2 and 3.


25.00
20.00
t
h
e
i
g
15.00

t
e
a

w
r
y
f

d

o
E
10.00
RA
A
G
RB
%
RC
5.00
PA
PB
PC
0.00
0
10
20
30
40
50
60
70
80
90
100
time (sec)

Figure 1 Total phenolic compounds of tea residue (R) and tea product (P) brewing at 3 temperatures versus
time where A, B, and C represent to 70, 80 and 90oC of brewing temperatures, respectively and error bars
showed the maximum and minimum values

Table 1 shows The rate constant, kobs, at different temperature, the intercept values (a) , and
the equilibrium concentration (C ). All the kinetics data are the averages of at least three
independent experiments. The rate constant of tea indicates that the total phenolics
infusion of tea residue was faster than tea product at all studied temperatures. It might be
due to the fact that, the rate of extraction depends on the area of the contact between the
phases, i.e., the rate of extraction is proportional to the surface area. Globular grain shape
of tea product formed in rolling step reduced the rate of water penetrating into the core.
On the other hand, tea residue has a thin flat shape which promoted a rapid extraction of
the phenolic compounds. Nevertheless, after tea products were exposed to water, the
surface area of the tea products and the tea residues were not highly different. The
phenolic compounds of tea product were destroyed by polyphenol oxidase during the
rolling step. Tea product was reprocessed in the cycle with mass breaking step around 50-
60 times and the tea residue was collected in each round. Therefore, higher total phenolics
content was found in tea residue compared to the tea product.

Figure 10 shows the Arrhenius plot for total phenolic compounds extracted from tea
residue and tea product. The linear plot of the obtained data indicates that extraction of
total polyphenols conforms to Arrhenius equation. The activation energies of tea residue
and tea product were obtained from the two linear curves in Figure 4 and they were 20.1
and 19.1 kJ/mol, respectively. The results of the determination by Arrhenius equation
indicated that the rate constant of phenolics infusion was more affected by the frequency
factor than the activation energy. The frequency factors of tea residue and tea product
were 2.21 and 0.72 s-1, respectively. The frequency factor relates with the collision rate
and steric factor which is constant and specific to each reaction. Compared to the tea
product, the tea residue yielded from tea manufacturing and broken tea leaves could affect
the mechanism of phenolics infusion which exhibited a higher rate of phenolics extraction.
The experimental data got agree well with the brewing kinetic model (E.q.1) which is the
first order kinetics [7; 8; 9].

1.00
0.90
0.80
y = 0.0019x + 0.2558
y = 0.0011x + 0.0586
0.80
0.70
2
2
R = 0.9854
R = 0.9969
0.70
0.60
-
c
)
0.60

-
c
)
0.50

0.50

/

(
c
0.40
c ∞
0.40

/

(
c
l
n
c ∞
0.30
0.30
l
n
0.20
0.20
0.10
0.10
0.00
0.00
0
60
120
180
240
300
0
60
120
180
240
300
Time (sec)
Time (sec)




Figure 2 First order plot for the infusion of % total phenolic Figure 3 First order plot for the infusion of % total phenolic
compounds of tea residue brewing at 70oC compounds of tea product brewing at 80oC

Table 1 Kinetics and equilibrium data for %total phenolic compounds of dry tea weight from tea residue brews and tea product brews
Brewing Temperature °C
Tea type
kobs/ 10-3s-1
a
C (%GAE)
R2

Residue
1.9
0.26
23
0.9762
70
Product
0.9
0.08
17
0.9945
Residue
2.4
0.25
23
0.9862
80
Product
1.1
0.06
20
0.995
Residue
2.8
0.35
23
0.9934
90
Product
1.3
0.09
20
0.9922

C

(1) k

obs = A e-(Ea/RT) (2)
ln
= k t + a




C

C
obs

Where: kobs = observed rate constant Ea = activation energy (kJ/ mol) R= gas constant (8.31441 J/ mol K) T= temperature (Kelvin)
A = frequency facto








25
25
t
) 20
t
) 20
h
h
e
i
g
e
i
g
15
15

t
e
a

w
Obs

t
e
a

w
Obs
r
y
r
y
2gr
2gr

(
d 10

(
d 10
E
1gr
E
1gr
A
A
G
G
%
5
%
5
Time (min)
Time (min)
0
0
0
10
20
30
40
50
60
70
80



0
10
20
30
40
50
60
70
80
Figure 4 Total phenolic compounds versus time of tea residue brewing at 70oC Figure 5 Total phenolic compounds versus time of tea residue brewing at 80oC
25
20
t
) 20
h
t
)
h 15
e
i
g
e
i
g
15

t
e
a

w
Obs

t
e
a

w
r
y
10
r
y

(
d
2gr
10
Obs
E

(
d
E
A
1gr
A
2gr
G
G
%
5
5
%
1gr
Time (min)
Time (min)
0
0
0
10
20
30
40
50
60
70
80



0
20
40
60
80
100
Figure 6Total phenolic compounds versus time of tea residue brewing at 90oC
Figure 7 Total phenolic compounds versus time of tea product brewing at 70oC
25
25
t
) 20
t
) 20
h
h
e
i
g
e
i
g
15
15

t
e
a

w

t
e
a

w
r
y
r
y

(
d 10
PB

(
d 10
Obs
E
E
A
2gr
A
2gr
G
G
%
5
1gr
%
5
1gr
Time (min)
Time (min)
0
0
0
20
40
60
80
100



0
20
40
60
80
100
Figure 8 Total phenolic compounds versus time of tea product brewing at 80oC
Figure 9 Total phenolic compounds versus time of tea product brewing at 90o

The extraction rate tended towards a constant which represented equilibrium concentration
and followed a first order rate (Figure 4-9). Normally 25-35% of the dry tea weight is
phenolic compounds of the young fresh tea leaves. There is no report analyzing the
amount of specification of phenolic compound and kinetics of phenolics extraction of
Oolong tea. The facts of multi-components and the mismatches prompted us to develop
model of two compounds with the first-order kinetics as shown by Eq. (2). The rate
constant of two groups, k1 and k2, and the equilibrium concentration, C∞,1 and C∞,2 at
various temperatures were obtained by minimizing the sum square errors between
measurement data and the integrated concentration value by using Eq. (3) (Table 2). The
equilibrium concentration of all brewing temperatures was assumed to be identical, since
the total amounts of phenolics compound should not depend on brewing temperature.
From the literature, the infusion rate constants of epicatechin, epigallocatechin,
epicatechin gallate and epigallocatechin gallate of Japanese green tea varies from 11.6 to
16.4 x 10-3s-1 with brewing at 80oC [10]. Hence, the first group of total phenolics
compound could possibly be the group of flavanols from tea residue which is the major
constituent in tea.
7.5
y = 2290.6x + 0.3312
Tea residue
2
R = 0.9987
Tea product
7
s
b

k
o 6.5
-
l
n
y = 2418x - 0.7949
2
R = 0.9898
6
1/T, K-1
5.5
0.0027
0.00275
0.0028
0.00285
0.0029
0.00295
Figure 10 Arrhenius plot of total phenolic compounds extraction from tea residue and tea product

dC
dC
dC
1
2
=
+



(3)
dt
dt
dt
where



dC



(4)
1 = k (C


C )
1
1
,
1
dt
and



dC



(5)
2 = k (C


C )
2
, 2
2,
dt

Table 2 Kinetics and equilibrium data for %total phenolic compounds of dry tea weight from tea
residue brews and tea product brews
Brewing Temperature
Tea
C∞,1
C∞,2
R2
°C
type
k1/ 10-3s-1
k2/ 10-3s-1
(%GAE)
(%GAE)
Residue
12.4
1.5
9.26
12.62
0.9888
70
Product
8.8
0.5
4.16
13.08
0.9954
Residue
16.3
1.7
9.2
13.07
0.9939
80
Product
9.9
0.6
4.11
16.27
0.9941
Residue
30.7
2.5
9.2
12.92
0.9912
90
Product
9.9
0.8
4.11
16.27
0.994








4. Conclutions

Total phenolic compounds concentration increased with extraction time and temperature
and approached a limiting equilibrium concentration (C∞) within 45 minutes. The brewing
kinetic was fitted very well with the first order model. Besides, the infusion of the tea
residue was faster than the tea product. Interestingly, this study suggested that tea residue
is rich in polyphenol compound and this should be further studied to convert this residue
to any value-added products.

5. References

[1] Department of Agricultural Extension, 2005, http://www.doae.go.th [Online],
Available: URL [18th July 2005].

[2]Shanghai
Cancer
Institute,
1994,
Cancer
Institute
[Online],
Available:
http://www.sjtu.edu.cn/english/research/institutes/caindex.htm [2006, Jan 18].

[3] Chu, D.C., Kim, M., Juneja, L.R. and Yamamoto, T., 1997, Chemistry and
Applications of Green Tea
, CRC Press, Boca Raton, 160 p.

[4] Atoui, A.K., Boskou, G., Kefalas, P. and Mansouri, A., 2005, “Tea and Herbal
Infusions: Their Antioxidant Activity and Phenolic Profile”, Food Chemistry, Vol. 89,
pp. 27-36.

[5] Sakanaka, S., Tachibana, Y. and Okada, Y., 2005, “Preparation and Antioxidant
Properties of Extracts Japanese Persimmon Leaf Tea (kakinoha-cha)”, Food Chemistry,
Vol. 89, pp. 569-575.

[6] Price, W.E. and Spiro, M., 1985, “Kinetics and Equilibrium of Tea Infusions. Rate of
Extraction of Theaflavin, Caffeine, and Theobromine from Several Whole Teas and
Sieved Fraction”, Journal of the Science of Food and Agriculture, Vol. 36, pp. 1309-
1314.

[7] Jaganyi,D. and Price, R.D., 1999, “Kinetics of Tea Infusion: the Effect of the
Manufacturing Process on the Rate of Extraction of Caffeine”, Food Chemistry, Vol. 64,
pp. 27-31.

[8] Jaganyi,D.. and Mdletshe,S., 2000, “Kinetics of Tea Infusion Part 2: The Effect of
Tea-Bag Material on the Rate and Temperature Dependence of Caffeine Extraction from
Black Assam Tea”, Food Chemistry, Vol. 70, pp. 163-165.

[9] Jaganyi, D., J. and Ndlovu, T., 2001, “Kinetics of Tea Infusion. Part 3: The Effect of
Tea Bag Size and Shape on the Rate of Caffeine Extraction from Ceylon Orange Pekoe
Tea”, Food Chemistry, Vol. 75, pp. 63-66.

[10] Jaganyi, D. and Wheeler, P.J., 2003, “Rooibos Tea: Equilibrium and Extraction
Kinetics of Aspalathin”, Food Chemistry, Vol. 83, pp. 121-126.


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