Aluminum Contents in Dry Leaves and Infusions of Commercial Black and Green Tea Leaves: Effects of Sucrose and Ascorbic Acid Added to Infusions

doi:10.4236/nr.2011.23019

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Natural Resources, 2011, 2, 141-145

doi:10.4236/nr.2011.23019 Published Online September 2011 (http://www.SciRP.org/journal/nr)

141

Aluminum Contents in Dry Leaves and Infusions

of Commercial Black and Green Tea Leaves:

Effects of Sucrose and Ascorbic Acid Added to

Infusions

Diego Armando Bárcena-Padilla, Marisela Bernal-González, Amalia Panizza-de-León, Rolando Sal-

vador García-Gómez, Carmen Durán-Domínguez-de-Bazúa

Facultad de Química, Universidad Nacional Autónoma de México, México City, Mexico.

Email: {die_gool_86, marisela_bernal2000}@yahoo.com.mx, [email protected], [email protected],

[email protected]

Received January 29th, 2011; revised June 28th, 2011; accepted July 10th, 2011.

ABSTRACT

Tea consumption has increased due to its beneficial effects. Results from a lab study on the effect of sucrose (5 g per

cup, 150 mL) and/or ascorbic acid (2 mL per cup, 150 mL) on dissolved aluminum compounds during the infusion of

two commercial types of dry tea leaves (black, green) with boiling water (5, 15 min infusion time) are presented. Fac-

tors influencing the presence of dissolved aluminum in the infusions of both tea leaves were infusion time and sugar

contents, as well as the interaction between ascorbic acid and sucrose (p < 0.05). Aluminum contents found after 15

min of infusion were 0.7 mg·L–1 for black tea infusions added with suga r, and 0.69 mg·L–1 for green tea added with both

sugar and ascorbic acid. Both concentrations are higher than the level accepted in Mexico for drinking water (there is

no act concerning tea infusions), that is 0.2 mg ·

–1.

Keywords: Aluminum Contents, Commercial Bl ack an d Green Tea Dry Leaves, Infusions, Sucrose, Ascorbic Acid

1. Introduction

Tea is one of the most popular non alcoholic drinks in the

world, particularly in Asia. In the last years tea consump-

tion, and particularly green tea, has increased, due to the

general belief that it has beneficial effects to human

health such as anti-mutagenic, anti-cancer, and anti-

oxidant properties [1]. Mexico, as other countries, has

increased its consumption at an annual rate of 20% [2,3].

Tea leaves (Camellia sinensis) are among the most

conspicuous vegetal species recognized as aluminum

accumulators, reaching contents up to 10,000 mg·kg–1 [4].

Commercial teas, in spite of the fact of being produced

from young leaves shoots, contain relatively high con-

centrations of aluminum, becoming a potential source of

bioavailable aluminum in the diet [5-9]. Matsumoto et al.

[4] have reported concentrations around 30,000 mg·kg–1

of aluminum in old tea dry leaves. Ruan and Wong [3]

mentioned concentrations of aluminum in some tea va-

rieties from 468 to 930 mg·kg–1. For many years alumi-

num has been considered innocuous for human beings

[10], since most chemical forms are not damaging for

living organisms. However, if pH soil values are low,

aluminum tends to form chemical species that are poten-

tially absorbed by plants, especially tea [11,12], and be-

come toxic for living organisms [13]. In this sense, there

has been controversy on the impact of this metal on bio-

logical systems particularly in the last years [14]. Con-

cerning human health recent studies have demonstrated

that bioavailable aluminum is related to some diseases

such as Alzheimer, Parkinson, and dialysis encephalopa-

thy [15].

Aluminum concentrations in tea products and its dis-

solution during the preparation of infusions has been

investigated by Flaten [16], Fung et al. [12], Moghaddam

et al. [17], and Wong et al. [8,18]. So far, the effects of

sucrose and/or lemon juice, as ascorbic acid, on the

leaching out of aluminum from the dry tea leaves to wa-

ter during infusion have not been assessed.

Aluminum Contents in Dry Leaves and Infusions of Commercial Black and Green Tea Leaves: Effects of Sucrose and

142

Ascorbic Acid Added to Infusions

The objective of this research was to quantify the con-

tent of dissolved aluminum in commercial green and

black dry leaves tea infusions adding or not sucrose

and/or ascorbic acid at two infusion times.

2. Materials and Methods

A previous market study was carried out in several Mex-

ico City supermarkets to determine which were the most

popular brands of commercial green and black tea among

the consumers [19]. As a result two brands, “A” for

green tea, and “B” for black tea, were chosen. Two ran-

domly chosen packages of each brand were taken and

brought to the laboratories. The contents of several

pouches were mixed to have a homogeneous lot for each

type of tea that would be subjected to a microwave di-

gestion. A single pouch contents of black and green tea

was also taken to corroborate if statistically significant

differences were found with the homogenized lot. The

covering material of one of the pouches that could be

leached out to the infusions (gauzy material) was ana-

lyzed to assess if aluminum was detected. From both

homogeneous lots 8 samples (4 for each type of tea) were

digested in a Berghof-MWS-1 microwave oven (Ger-

many), according to Bárcena-Padilla [19] pre-established

conditions. To determine the contents of aluminum of the

samples, atomic absorption spectroscopy (AAS) was the

technique used. Analyses were carried out in the Labo-

ratory for Atomic Absorption of the UNAM Faculty of

Chemistry (Laboratorio de Absorción Atómica de la

USAI, Unidad de Servicios de Apoyo a la Investigación,

Facultad de Química, UNAM). The same technique was

used for the infusions.

2.1. Characterization of the Infusions

A four-factor experimental design with two levels per

factor was performed, considering duplicates for all sam-

ples. Figure 1 shows the experimental design.

Figure 1. Experimental design for the preparation of green

and black tea infusions (5, 15 min) with and without sucrose

and ascorbic acid simulating lemon juice.

Factor 1: Tea type (Green and black tea leaves).

Factor 2: Ascorbic acid addition to simulate lemon

juice (With and without addition, 2 mL).

Factor 3: Sucrose contents (With and without addition,

2 teaspoons = 5 g).

Factor 4: Infusion time (5, 15 minutes).

Commercial bottle drinking water was brough to boil-

ing temperature and 150 mL were poured on each of the

beakers that contained the tea leaves pouches. Sucrose (ca.

5 g), and/or ascorbic acid (ca. 2 mL), were also added.

Infusion times considered were 5 and 15 minutes. After

the infusion time was over, liquid was drained. There were

32 samples to be digested and sent to AAS analysis. Water

was also analyzed to determine its aluminum contents,

since in Mexico many potabilization plants use aluminum

compounds within the process [20]. Aluminum contents

found in water were deducted from the one determined in

the infusions.

Statistical analyses of all experimental data were car-

ried out using Statgraphics Plus 5.

3. Results and Discussion

Table 1 presents the concentrations of aluminum found

in the dry leaves of both commercial teas considered. As

mentioned before, black and green tea commercial

brands selected were those with the highest demand in

several supermarkets, in Mexico City, according to a

preference study previously performed [19].

These contents agree with literature data reported by

other researchers [3,4,17].

Sucrose and drinking water were analyzed to corrobo-

rate its aluminum contents. Also, the material of one

pouch was analyzed for aluminum contents.

Table 2 shows the results found. These results indicate

that sugar and the pouch material were not a factor to be

considered. However, drinking water had very high alu-

minum contents, probably due to the potabilization

methods commonly used in Mexico (that include the

addition of alum to flocculate and precipitate water im-

purities). This amount was deducted from the infusions

data obtained from the atomic absorption analyses.

Table 3 shows the data obtained from the infusions

obtained for both types of tea. All of them exceed the

maximum allowed contents for drinking water of the

Mexican Standards, 0.2 mg·L−1 or 0.2 mg·kg−1 [21].

According to the variance analysis, no significant

differences among the two commercial tea dry leaves

types, black and gree, were found (p < 0.05).

Concerning the infusions, the amount of aluminum

transferred to the liquid phase was statistically different

depending upon tea type, infusion time, and sucrose

presence (Table 4).

Aluminum Contents in Dry Leaves and Infusions of Commercial Black and Green Tea Leaves: Effects of Sucrose and 143

Ascorbic Acid Added to Infusions

Table 1. Concentrations of aluminum in commercial black and green dry tea leaves.

Aluminum contents in dry leaves (ppm or

mg·kg−1)

Aluminum percentage (% d.m.) Aluminum contents per pouch of tea

(mg)

Green tea Black tea Green tea Black tea Green tea Black tea

Media 1322.56 1114.20 0.13 0.11 1.28 1.08

S. D. 256.91 58.61 0.03 0.01 0.26 0.05

V. C. 19.42 5.26 23.07 9.09 20.31 4.62

S. D.: standard deviation, V. C.: variation coefficient, d. m.: dry matter.

Table 2. Concentrations of aluminum found in sucrose, water, and pouches material.

Sample Aluminum contents (ppm or mg·kg−1)

Sucrose < D. L.

Pouch material < D. L.

Dinking water (commercial carafe) 1.55

D. L.: Detection limit.

Table 3. Aluminum concentrations in black and green tea infusions.

Treatments Aluminum in black tea infusions

(ppm or mg·kg−1) Media

Aluminum in green tea infusions

(ppm or mg·kg−1) Media

T-5 (5 min infusion) 0.46 ± 0.00 0.61 ± 0.00

T-15 (15 min infusion) 0.65 ± 0.05 0.65 ± 0.05

T-A-5 (5 min, ascorbic acid added) 0.34 ± 0.05 0.57 ± 0.16

T-A-15 (15 min, ascorbic acid added) 0.57 ± 0.05 0.46 ± 0.00

T-S-5 (5 min, sucrose added) 0.53 ± 0.00 0.53 ± 0.00

T-S-15 (15 min, sucrose added) 0.70 ± 0.00 0.61 ± 0.00

T-A-S-5 (5 min, ascorbic acid + sucrose added) 0.65 ± 0.05 0.57 ± 0.05

T-A-S-15 (15 min, ascorbic acid + sucrose

added) 0.61 ± 0.00 0.69 ± 0.00

A: ascorbic acid added, S: sucrose added, T: tea leaves.

Table 4. Variability analysis for aluminum dissolved in black and green tea infusions.

Factors Square values sum d.f. Medium Square Coefficients F P Value

A) Tea type

(green/Black) 0.0047531 1 0.0047531 0.89 0.3570

B) Ascorbic acid 0.0087781 1 0.0087781 1.64 0.2145

C) Sucrose 0.0399031 1 0.0399031 7.45 0.0126

D) Infusion time 0.0552781 1 0.0552781 10.32 0.0042

Interactions

A-B 0.0003781 1 0.0003781 0.07 0.7931

A-C 0.0157531 1 0.0157531 2.94 0.1011

A-D 0.0215281 1 0.0215281 4.02 0.0581

B-C 0.0427781 1 0.0427781 7.98 0.0101

B-D 0.0094531 1 0.0094531 1.76 0.1983

C-D 0.0000781 1 0.0000781 0.01 0.9050

Residues 0.112516 21 0.0053578

Total (Corr.) 0.311197 31

Quotients F are based on the quadratic mean residual error (d.f. degrees of freedom). P value is the probability of obtaining a test statistic (which is a

function of the sample; it is considered as a numerical summary of a set of data that reduces the data to one or a small number of values that can be used

to perform a hypothesis test) at least as extreme as the one that was actually observed, assuming that the null hypothesis is true (general or default

position, such as that there is no relationship between two measured phenomena, or that a potential treatment has no effect).

Aluminum Contents in Dry Leaves and Infusions of Commercial Black and Green Tea Leaves: Effects of Sucrose and

144

Ascorbic Acid Added to Infusions

Irrespective of the type of tea, infusion time is an im-

portant factor concerning the amount of dissolved alumi-

num. In the case of sucrose, it seems this factor is relevant,

since its chemical structure may be inducing the release of

aluminum from the polyphenol complex structures in tea.

This might be an important line of research to be followed

in the future, especially in those countries where sugar is

added at the time of leaves infusion.

Also, aluminum speciation should be carried out, since

some chemical species are more prone to be biologically

active [9,22-26].

4. Conclusions and Recommendations

Contents of aluminum in the most widely consumed

commercial dry leaves of green and black tea found in

Mexico City’s supermarkets and its infusions were as-

sessed. Average concentrations are higher in green tea

with respect to black tea but the differences were not

statistically significant (p < 0.05).

Statistically (p < 0.05), the most influencing factors in

the infusions of both types of tea were the infusion time

and the sugar contents (sucrose). Also, the interaction of

ascorbic acid and sucrose seemed to play a role, particu-

larly with black tea.

According to the Mexican Standards for drinking wa-

ter [21], the maximum concentration of aluminum is 0.2

ppm. For the infusions, the drinking water contents were

deducted from the total values obtained for all infusions,

and even though all of them exceeded this norm.

Commercially sold drinking water in Mexican super-

markets, and used in these experiments, contained 1.55

ppm aluminum, a value far exceeding this limit, a fact

that should be assessed by the sanitary authorities in

Mexico. Finally, it is recommended to assess the alumi-

num species found in the dry tea leaves and in the infu-

sions to evaluate its bioavailability for potential consum-

ers [7,9,23,25,27].

5. Acknowledgements

One of the authors acknowledges the scholarship granted

to pursue doctoral studies to UNAM (National Autono-

mous University of Mexico in Spanish) Coordination for

Graduate Studies. Materials were partially acquired with

a UNAM DGAPA project (PAPIME PE101709 “Apoyo

a la enseñanza experimental de las asignaturas terminales

de las carreras que se imparten en la Facultad de Química

de la UNAM”). Authors appreciate the technical support

from M.A.I. Landy Irene Ramírez-Burgos.

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