Determination of Minerals in Herbal Infusions Promoting Weight Loss
Biol Trace Elem Res
Determination of Minerals in Herbal Infusions Promoting Weight Loss
Wioletta Samolińska 0 1
Bożena Kiczorowska 0 1
Małgorzata Kwiecień 0 1
Elżbieta Rusinek-Prystupa 0 1
0 Department of Biochemistry and Toxicology, University of Life Sciences , Akademicka 13, 20-950 Lublin , Poland
1 Department of Animal Nutrition, University of Life Sciences , Akademicka 13, 20-950 Lublin , Poland
2 Wioletta Samolińska
The study aimed at determination of the mineral composition of slimming herbal teas and estimation of the coverage of their total intake with infusions in women's daily diet. The content of Na+, K+, Ca+2, Mg+2, Zn+2, Cu+ 2, Fe+2, and Mn+2 was determined in infusions and mineralisates obtained from the slimming herbal teas. Among macroelements, the highest content was recorded for Ca-on average 3.73 mg·100 ml−1 in its infusion. Mn was a microelement with the highest concentration amounting to 0.20 mg·100 ml−1 in the infusion. The investigations revealed that, referring to the dietary reference intakes (DRIs), weight loss herbal infusions cover the recommended daily intake of manganese for women to the highest extent (on average 54 %), which suggests that they can be a major source of this microelement for the organism. Herbal teas only to a slight extent (to approx. 4 %) covered the recommended daily intake of magnesium, sodium, potassium, iron, zinc, copper, and calcium in the daily diet.
Herbal teas; Weight loss; Macroelements; Microelements; Dietary reference intakes
-
Department of Bromatology and Food Physiology, University of Life
Sciences, Akademicka 13, 20-950 Lublin, Poland
Introduction
Tea is one of the most popular beverages in Poland and in the
world. Every year, Poles use on average ca. 1 kg of tea to
prepare the beverage, which places Poland among the ten
top consumers of tea in the world (eighth place in the world
and fourth in Europe) [
1
]. This beverage owes its popularity to
the variety of flavours and the healthy properties of tea
associated with the content of many bioactive compounds. The
term ‘tea’ is currently used to describe not only black, green,
red, or white tea but is also used in reference to herbal
infusions obtained from plants other than Camellia. ‘Teas’ also
denote mixes of dried fruit, herbs, seasonings, and various
additions. Frequently, the recipe of such a mix does not
contain tea leaves at all. Depending on the composition, they are
used, among other applications, in herbal medicine or in
weight loss treatments. Such tea infusions are often consumed
several times a day [
2, 3
]. Since consumers are interested in
herbal teas enhancing body weight reduction, it is important to
determine their nutritive value. This is particularly significant
for women, as they choose weight loss therapy more
frequently than men do [
4
].
The study aimed at determination of the mineral
composition of slimming herbal teas and evaluation of the coverage of
the recommended daily intake of mineral elements by tea
infusions in women.
Material and Methods
Material
The content of selected macroelements and microelements
was determined in the group of weight control products.
The studied material comprised nine different kinds of tea
from four Polish producers (in 2-g tea bags, 20 in each
package) available in Lublin (N 51°14′53″, E 22°34′13″)
and purchased in 2012. Table 1 presents data on the
composition of the slimming herbal teas (denoted as A, B, C,
D, E, F, G, H, and I) and producer’s recommendations of
the daily intake. Three packages of each product were
analysed. The products were purchased in different shops
in order to have material from three different production
batches of each herbal tea type. All teas were ahead of their
best-before dates. Five tea bags were taken from each
purchased package of each kind of tea, and the dried tea leaves
were used as a collective sample for further analysis.
Mineral Analysis of Slimming Herbal Tea Samples and their Infusions
In total, 54 samples of nine different types of herbal tea were
analysed (dry tea and infusions). Six samples were analysed
from each kind of herbal tea. The chemical analysis involved
determination of the content of Na+, K+, Ca+2, Mg+2, Zn+2,
Cu+2, Fe+2, and Mn+2 in mineralised tea samples (n = 3) and
infusions (n = 3). The contents of the elements were
determined in the tea materials (2 g of herbal material) after
incineration in a muffle furnace at 450 °C. The resultant ash was
solubilized on crucibles using 6 mol l−1 of spectrally pure
hydrochloric acid (POCH, Poland). Na and K were analysed
using flame atomic emission spectroscopy (FAES) with a
flame photometer (Pye Unicam SP 2900, Cambridge, UK)
at a wavelength of λ = 589.0 and λ = 766.5 nm, respectively.
Ca, Mg, Zn, Cu, Fe, and Mn concentrations were determined
using flame atomic absorption spectroscopy (FAAS) with a
SOLAAR 939/959 spectrophotometer (Unicam, Cambridge,
UK). Calcium was determined at λ = 422.7 nm, magnesium at
λ = 285.2 nm, zinc at λ = 213.9 nm, copper at λ = 324.8 nm,
iron at λ = 248.3 nm, and manganese at λ = 279.5 nm [
5
]. In
the case of Na and K determinations, cesium chloride (Merck,
Poland) was added to the standards and samples as an
ionization buffer at a concentration of 0.2 % w/v. Ca and Mg were
analysed by addition of 0.4 % w/v lanthanum oxide (Merck,
Poland), which is a correction buffer that allows binding of the
analysed element to the matrix. The percentage of extraction
of the elements into the infusion in the course of brewing was
determined. The herbal infusion was made by pouring 200 ml
of boiling ultrapure water obtained from a HLP 5 system
(Hydrolab, Gdansk, Poland) over a 2-g tea sample (loose).
Ultrapure water was used in all analyses. The brewing time
was approximately 10 min—as recommended by the producer
on the package. The infusions were drained, and the residue
on the drain was flushed with hot water. The prepared herbal
tea infusions (10 ml) were placed in PP tubes and acidified
with HNO3 (POCH, Poland) to a concentration of 0.25 mol l−1
[
6
]. The concentrations of the elements in the infusions were
determined using the methods described above.
The analytical facilities and their quality control system are
certified under PN-EN ISO/IEC 17025:2005 [
7
]. The
accuracy of the analytical procedure was verified by an analysis of
certified reference materials Mixed Polish Herbs
(INCTMPH-2), manufactured by the Institute of Nuclear
Chemistry and Technology (Warsaw, Poland). The recovery
levels (n = 3) and relative standard deviations (RSD) for the
analysed elements were as follows: Na (102.3 %, 6.4 %); K
(96.4 %; 7.5 %); Ca (99.7 %, 8.6 %); Mg (100.7 %, 3.9 %); Zn
(102.0 %, 4.7 %); Cu (94.6 %, 7.9 %); Fe (94.5 %, 8.2 %); and
Mn (96.8 %, 6.9 %).
Oxalate Analysis in Infusions
Additionally, the content of soluble oxalates was determined
in the three infusions for each herbal tea. The manganometric
method [
8
] was adopted from Rusinek et al. [
9
]. Ten millilitres
of the infusions was taken for analysis and transferred to
centrifuge tubes. Five millilitres of 5 % CaCl2 and 5 ml of acetone
were added and mixed. Then, the solutions were cooled at
5 °C for 30 min and centrifuged for 15 min (3000 rpm). The
sediment was transferred to the flask with 5 ml 10 % H2SO4
and heated on a water bath (70 °C) until dissolution. Titration
in hot temperature was conducted with a 0.0224 mol l−1
solution of KMnO4 until pink colour appeared and remained for
ca. 1 min.
Statistical Analysis
The normality and homogeneity of variance data of the
mineral composition were tested using the Shapiro-Wilk and
Brown-Forsythe tests, respectively. The non-parametric
Kruskal-Wallis test (a non-parametric equivalent of one-way
analysis of variance) was used to analyse differences in
element concentrations in the herbal teas. The performed test
showed a normal distribution of the manganese concentrations
determined in the herbal tea as well as zinc and iron in the
infusions. Detailed comparisons between the groups were
conducted using the post hoc Dunn test. All statements of
significance were based on a probability of <0.05 and <0.01.
The Pearson correlation coefficient was calculated for the
content of oxalate acid and calcium in the infusions. All
calculations were performed with statistical software package
Statistica version 10 [
10
].
The intakes of Na, K, Ca, Mg, Zn, Cu, Fe, and Mn with
daily tea portions (Table 1) were evaluated using the dietary
reference intakes (DRIs) (estimated average requirements—
EAR and adequate intakes—AI) for adult women, based on
the recommendations of the US National Academy of
Sciences (NAS), Institute of Medicine (IOM), and Food and
Nutrition Board (FNB) [
11
] and Polish recommendations of
the National Food and Nutrition Institute [
12
].
* Assuming that one serving of herbal infusion is 200 ml
Results and Discussion
Content of Na, K, Ca, Mg, Zn, Cu, Fe, and Mn in Herbal
Teas and their Infusions
As regards macroelements, the herbal teas selected for the
study contained the highest amount of calcium, and
manganese was a predominant microelement (Table 2). Similar
concentrations of elements were determined in the evaluated
herbal teas and their infusions. The following contents of
minerals were determined for tea as a market product:
Ca > Mg > K > Mn > Na > Fe > Zn > Cu (in a descending
order), whereas the order in the herbal infusions was
Ca > Mg > K > Na > Mn > Zn > Fe > Cu.
The results of our investigations were compared with
results of similar studies involving the analysis of the elemental
composition of teas (black, green, red), herbal teas, and
slimming herbal teas.
The determined content of calcium was from 266.90 to
1407.07 mg·100 g−1 and that of magnesium ranged from
173.75 to 474.45 mg·100 g−1 of the market product
(P < 0.01) (Table 2). The results obtained in this study and
by other authors suggest that Ca and Mg are present in
medicines of plant origin and teas with varied composition (herbs,
teas, fruits, bioactive ingredients) in considerable amounts [
2,
13, 14
]. Garcinia cambogia widely used as a component of
slimming formulations can be an example. Commercial
samples of G. cambogia extracts contain calcium salt of HCA
((−)-hydroxycitric acid) for its stability [15]. In this study, its
content in herbal teas C and H may contribute to the increased
calcium amounts. The highest content of this element was
noted in herbal tea I (P < 0.01), which was probably attributed
to the presence of senna (Senna alexandrina Mill.), which
contains 898.9-mg calcium in 100 g−1, as indicated by
Ebrahim et al. [
16
].
In the presented study, the amount of potassium in the
herbal teas did not exceed 222 mg·100 g−1 and that of
sodium was lower than 90 mg per 100 g of the market
product. Available literature indicates that the level of
potassium and sodium in teas varies considerably
depending on the origin of the plant material. It can even vary for
the same type of tea [
13, 17, 18
]. The highest potassium
content (P < 0.01) was determined in herbal tea C, which
can be associated with the presence of kola nuts (Cola
spp.) in its composition, which contain substantial
amounts of this element (348.47 mg·100 g−1 d.m.) [
19
].
The content of zinc was determined in the weight loss
herbal teas in a broad range from 2.93 to 23.76 mg·
100 g−1, and the content of iron was from 13.41 to
37.48 mg·100 g−1 (P < 0.01). Such a span can be
connected with the rich ingredient composition of the studied
products. Other authors reported less diverse results
concerning the content of these elements in slimming teas
[
14, 20
]. In the infusion of herbal tea B, with Yerba mate
(Ilex paraguariensis A. St.-Hil.) as the main ingredient,
the highest zinc content was noted (P < 0.05). This was
confirmed by the investigations conducted by Bragança
[21], who reported slightly higher zinc contents in
infusions of only this type of tea (0.041 to 0.10 mg·100 ml−1).
In turn, the amount of copper recorded in our study (0.42 to
1.85 mg·100 g−1) was similar to that reported by other authors
(from 0.72 to 1.54 mg·100 g−1) [
14, 20
].
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The content of manganese was determined in a range from
14.82 to 73.05 mg·100 g−1 of herbal tea (P < 0.01). The results
were close to those reported by other authors [
14, 20, 22
].
Similarly, in the case of manganese, the presence of Yerba
mate in the composition may have contributed to the higher
amounts of this element in the infusions of herbal teas C, B,
and E (0.33–0.30 mg·100 ml−1). Considerable amounts of Mn
in Yerba mate infusions (0.27–0.70 mg·100 ml−1) were also
reported by Bragança [
21
].
The degree of extraction of the elements into the infusion
was as follows: Na > K > Mg > Mn > Ca > Cu > Zn > Fe (in a
descending order) (Table 2). The highest percentage of
extraction into the infusion was determined for sodium and
potassium (over 80 %), and nearly half of the manganese was
transferred to the infusion. On average, up to 40 % of copper and
zinc were extracted into the beverage. The weakest transfer
into the herbal tea was noted for iron (on average less than
6 %). Similar results were reported by other authors [
2, 14,
20
]. For manganese and calcium, the average degree of
extraction was higher than that recorded by the abovementioned
authors. For manganese, it was above 70 % (48.11–88.41 %)
and for calcium above 40 % (19.98–54.88 %). A similar level
of solubility of the analysed elements in slimming herbal teas
was observed by Szymczycha-Madeja et al. [14], who also
reported a high percentage of transfer of manganese into the
infusion (72.9–88.4 %) and a moderate percentage for calcium
(21.5–54.5 %).
The degree of extraction of minerals into the infusion is
modified by many factors and is determined, among other
things, by the method of infusion preparation, brewing time,
type of plant material used, tea components, and the form of
market product (tea leaves or tea bags). The content of such
compounds as tannins or oxalic acid in tea can reduce the
absorption of minerals as well [
9, 23
]. In the presented study,
the following content of oxalic acid was determined in the
respective teas—17.11 mg (tea A), 34.21 mg (B), 24.02 mg
(C), 24.06 mg (D), 60.01 mg (E), 26.01 mg (F), 22.02 mg (G),
16.01 mg (H), and 18.05 mg (I) per 100 ml of tea. These
values were negatively correlated with the concentration of
calcium (r = −0.539). A higher content of oxalic acid was
noted by Rusinek [9], who determined the content of this
anti-nutritive component in black tea (on average
115.68 mg·100 ml−1), green tea (87.64 mg·100 ml−1), and
red tea (101.91 mg·100 ml−1). The author also noted a lower
content of oxalates in infusions from bagged tea compared to
loose-leaf tea and observed a similar relationship for teas with
an admixture of other plant components (apple, hibiscus, briar,
or grapefruit), compared with teas from Camellia genus
plants. Herbal tea E characterised by the highest content of
o x a l a t e s c o n t a i n e d P u - e r h t e a a s w e l l a s k o n j a c
(Amorphophallus muelleri Blume), which probably
contributed to the high level of these compounds in the infusion, since
the plant contains substantial amounts thereof in all its parts
[
24
]. Besides plants from the genus Camellia, the stinging
nettle (Urtica dioica L.) may have been a rich source of oxalic
acid in the analysed beverages (herbal tea B). This is
confirmed by investigations conducted by other authors.
Sperkowska and Bazylak [25] determined a level of
59.91 mg of soluble oxalates per 100 ml of nettle infusion.
Herbal tea B contained fennel seeds, which may have
increased the content of water-soluble oxalates in the infusion.
As reported by Al-Wahsh [
26
], seeds of fennel (Foeniculum
vulgare Mill.) contain 1086 mg of total oxalate in 100 g−1 dry
weight and 194 mg of soluble oxalates in 100 g−1 dry weight.
Another ingredient of the analysed herbal teas, G. cambogia,
is characterised by a twofold higher content of water-soluble
oxalates (137.52 mg·100 g−1 d.m) [
27
]. However, the
proportion of G. cambogia in the analysed beverages is low; hence,
its effect on the content of soluble oxalates in teas C and H is
probably insignificant.
Small amounts of soluble oxalates are also contained in the
fruit components of the analysed types of herbal tea. Their
content in apples is 2.2 mg·100 g−1 fresh weight and in
oranges 2.9 mg·100 g−1 fresh weight [
26
]. The literature does
not provide data on the content of soluble oxalates in the other
plant ingredients of the analysed herbal tea, i.e. in hibiscus,
rosehip fruit, lotus flowers, and others, which makes the
interpretation of the results difficult.
Teas, herbal, and/or fruit teas also contain non-essential and
toxic metals, e.g. Al, Cd, Ni, or Pb, which are extracted into
the infusion and may pose a health hazard to consumers.
Commission Regulation (EC) no. 629/2008 of 2 July 2008,
amending Regulation (EC) no. 1881/2006 set maximum
levels for certain metals in food supplements: lead
(3.0 mg·kg−1), cadmium (1.0 mg·kg−1), and mercury
(0.10 mg·kg−1) [
28
]. The maximum allowable level of these
elements applies to dietary supplements in the commercial
form. In the investigations carried out by Jeszka-Skowron
[
29
], the Al content in green tea infusion and black tea
infusion was negligible, i.e. 0.008 and 0.011 %, respectively. In
the study reported by Łozak [
20
], in which the mineral
composition of slimming herbal tea was analysed, the
concentrations of cadmium and lead in all samples were below the EC
maximum level for Cd and Pb. In this study, the levels of these
heavy metals were not determined.
Dietary Intake of Minerals from Slimming Herbal Tea
Infusions
The daily intake of the studied elements from the infusions
of weight loss herbal teas was analysed and presented as a
percentage of dietary reference intakes (DRIs) for adult
women [
11, 12
] (Table 3). In this study, the bioavailability
of elements from the infusions in vivo was not determined.
We only analysed the effect of soluble oxalates on calcium
a v a i l a b i l i t y f r o m t h e i n f u s i o n s . T h e r e f o r e , t o t a l
The calculated daily intake of elements with herbal infusions and realization of DRI values
DRI*
A
concentrations of other elements in the herbal infusions
were compared with the DRI values. The elements can be
divided into three groups, depending on the degree of
coverage of the organism’s demand: elements present in tea in
inconsiderable amounts, such as iron, sodium, and
potassium, covered the recommended daily intake only up to ca.
1 % (0.04–1.23 %). The second group comprises
components such as magnesium, copper, calcium, and zinc, the
requirement for which was covered by the tea infusions at a
low level—up to ca. 4 % (0.46–4.37 %). The third group
included only manganese present in the infusions in
considerable amounts and covering the standard nutrition
requirement in a wide range from 9.91 to 99.68 %. On
average, it covered more than a half of the dietary reference
intake (54.36 %) for adult women. In their study, Powell et
al. [
30
] analysed the bioavailability of manganese from tea
infusions by incubation thereof in human gastric acid
(37 °C, 1 h). A single serving of tea (225 ml) covered
10 % of the daily intake of this element in a potentially
bioavailable form. Reference literature reports that
manganese is the only element occurring in tea—mostly black
tea—in considerable amounts from the point of view of
nutrition [
14, 20, 30
]. In the daily diet, manganese is
mainly consumed with food products of plant origin and
with water, but only a small percentage (1–4 %) is
absorbed in the alimentary tract [
31
]. This element also
takes part in the formation of bone and connective tissue
and is a component or an activator of enzymes. It also
participates in the metabolism of amino acids,
carbohydrates, and cholesterol [
32
]. Some epidemiological studies
report adverse neurological effects of exposure to very
high levels of manganese in drinking water [
30
].
Women tend to absorb more manganese than men do
[
31, 32
]. Given this fact and the considerable content of
this element in herbal infusions, the percentage share of
manganese was also calculated with reference to the
standard upper level (UL), i.e. 11 mg day−1 for an adult
woman [32]. This standard is the maximum biologically
tolerable customary level of intake of the mineral component
that has no adverse effect on health in 97.5 % of people in
a population [
11, 12
]. The corresponding values in the
presented study ranged from 1.622 % (herbal infusion
G) to 16.31 % (herbal infusion E), reaching on average
8.90 % of the standard UL, which indicates that slimming
herbal teas can be safely used on a daily basis. To fully
assess a given food product or beverage as a source of
Fe
elements in the diet, the total contents of elements not
only in vitro but also in vivo should be determined. This
would facilitate absorption of these elements in the
digestive tract, which is dependent on their bioavailability.
However, this type of research is conducted extremely
rarely, as it is cost- and time-inefficient and sometimes
disputable [
30, 33, 34
].
Conclusion
The studied slimming herbal teas contained different amounts
of minerals. Calcium and magnesium were the predominant
elements determined therein and manganese and iron were the
most abundant microelements. Weight loss herbal infusions
cover the recommended daily intake at a low level—up to
ca. 4 %. In turn, the high content of manganese and the
coverage of, on average, more than half of the dietary reference
intake of this element, suggest that slimming herbal infusions
can be a major source of this element in the daily diet.
Compliance with Ethical Standards
Conflicts of Interest The authors declare that they have no conflict of
interest.
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