The bioactive and mineral compounds in the birch sap collected in different type of habitats.

Abstract

Birch sap is used as a traditional drink and in traditional medicine in many countries in the northern hemisphere. However, there are scarce data on the antioxidant properties, nutrients and the mineral content of birch saps. In this study, the above-mentioned properties were analyzed in two different birch species Betula pendula Roth (silver birch) and Betula pubescens Erth. (downy birch) in various areas (suburban, traffic and industrial). The current study evidenced significant differences between the antioxidant, nutrition and mineral content, depending on the type of habitat, not on species. It was shown that higher antioxidant properties, sugar and protein content were detected for silver birch sap from industrial area, which may be due to the response of plants to environmental stress. Moreover, heavy metals presenting in soil were not detected or detected at low concentrations in the sap. Birch sap can be used as a valuable natural beverage, which is especially important nowadays, when there is a pressure to minimize the use a synthetic and artificial food ingredients.

Full text

Introduction
In the olden days, the sap of spring trees was
frequently used in traditional medicine in forested ar-
eas of northern hemisphere. In Europe, the main source
of tree sap was birches: Betula pendula Roth. (silver
birch), Betula pubescens Ehrh. (downy birch) (Jones
2011, Svanberg et al. 2012). Birch sap was known as
valuable antidote against scurvy, kidney, stomach and
liver diseases, for gall stones, skin diseases and as a
nutritional drink. It was used also in veterinary and
as a cosmetic product  hair conditioner. Nowadays,
the birch sap has become more and more popular as
natural probiotic, after fermentation (Semjonovs et al.
2014). Its tapping is carried out in Russia, Belarus,
Ukraine, Latvia, Estonia and also in Korea, Japan and
China at large scales (Svanberg et al. 2012, Kûka et
al. 2013). The best time for the birch sap harvesting
depends on geographical location, climate and weather
course. In central Europe it is late March and early
April, with later start toward the north. Generally, birch
tree can secrete sap from two to four weeks and its
yield depends on birch species (Kallio and Ahtonen
1989, Jiang et al. 2001, Peev et al. 2010). Birch sap is a
transparent or a slightly opalescent fluid. It tastes
The Bioactive and Mineral Compounds in Birch Sap
Collected in Different Types of Habitats
DOROTA GRABEK-LEJKO1*, IDALIA KASPRZYK2, GRZEGORZ ZAGUÙA3, AND CZESÙAW PUCHALSKI3
1University of Rzeszów, Department of Biotechnology and Microbiology, Zelwerowicza 4 St., 35-601 Rzeszów,
Poland
2University of Rzeszów, Department of Environmental Biology, Zelwerowicza 4 St. 35-601 Rzeszów, Poland
3University of Rzeszów, Department of Bioenergy and Food Science, Zelwerowicza 4 St. 35-601 Rzeszów, Poland
*Correspondence author: dorobek@o2.pl; phone: 0048 17 7855438.
Grabek-Lejko, D., Kasprzyk, I., Zaguùa, G. and Puchalski, Cz. 2017. The Bioactive and Mineral Compounds
in Birch Sap Collected in Different Types of Habitats. Baltic Forestry 23(2): 394-401.
Abstract
Birch sap is used as a traditional drink and in traditional medicine in many countries in the northern hemisphere.
However, there are scarce data on the antioxidant properties, nutrients and the mineral content of birch saps. In this
study, the above-mentioned properties were analyzed in two different birch species Betula pendula Roth (silver birch)
and Betula pubescens Ehrh. (downy birch) in various areas (suburban, traffic and industrial). The current study evidenced
significant differences between the antioxidant, nutrition and mineral content depending on the type of habitat, not on
species. It was shown that higher antioxidant properties, sugar and protein content were detected for silver birch sap
from industrial area, which may be due to the response of plants to environmental stress. Moreover, heavy metals
presenting in soil were not detected or detected at low concentrations in the sap. Birch sap can be used as a valuable
natural beverage, which is especially important nowadays, when there is a pressure to minimize the use synthetic and
artificial food ingredients.
Key words: Antioxidants, Betula pendula, Betula pubescens, birch sap, minerals, nutrients, heavy metals.
similar to water and is slightly sweetish (Peev et al.
2010). It contains many bioactive compounds. The total
amino acid concentration ranges from 100 to 500 mg·L-1.
Among free amino acids glutamine, citrulline, glutam-
ic acid, isoleucine, valine and asparagine are the most
often detected. They represent 9296 % of the total
amino acid content. Their concentrations change dur-
ing flow season (Kallio et al. 1985, Kallio and Ahto-
nen 1989). In Japan, the maximum of the total amino
acid content of silver birch was above 50 mg·L-1 and
reached this value at the end of the flow season (Jiang
et al. 2001, Jeong et al. 2012).
The total sugar content oscillates from 1% in Fin-
land and 2.5-2.6% in Poland. The dominant carbohy-
drates are glucose and fructose. Their concentrations
range between 2-5gL-1 in equal proportions each of
them representing over 80% of total sugar. The con-
tent of sucrose is three to ten time less than fructose
or glucose content (Kallio et al. 1985, Kallio and Ahto-
nen 1987, Kûka et al. 2013, Ùuczaj et al. 2014).
Birch sap also contains valuable minerals. Calci-
um and potassium occur in the highest concentrations.
In Latvian silver birch sap, the mean content of Ca ranged
from 41 to 150mgL-1 and K from 41 to 142mgL-1 (Kûka
et al. 2013, Vincçvièa-Gaile 2014). In many samples, Zn,
D. GRABEK-LEJKO ET AL.
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THE BIOACTIVE AND MINERAL COMPOUNDS IN BIRCH SAP /.../
ISSN 2029-9230
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2017, Vol. 23, No. 2 (45)

Mg, Mn, Cu, Cd, Fe and Na were detected (Jeong et
al. 2012, Kûka et al. 2013, Vincçvièa-Gaile 2014, Bilek
et al. 2015a). In Polish samples, the contents of these
minerals were lower and the variability between indi-
vidual trees was much higher (Bilek et al. 2015a).
The problem of the chemical composition of tree
sap was frequently investigated in the 80s and 90s of
the 20th century. Much less attention has been paid
to the bioactive properties (Klinger et al. 1989). Lee
et al. (2009) observed a weak inhibitory effect on mi-
crobial growth, as well as phagocytosis-influencing,
antiphlogistic and antipyretic activities. The question
of impact of the type of habitat on the nutrient and
mineral content was also very rarely investigated
(Vincçvièa-Gaile 2014). Due to the increasing use of
birch sap, an exact knowledge of its properties seems
to be justified.
This research was aimed to evaluate antioxidant
properties, nutrient and mineral content of fresh sap
of two birch species B. pendula Roth. and B. pubes-
cens Ehrh. The goal of this study was to verify the
preliminary hypothesis that the type of habitats (like
soils with heavy metals content) and birch species
affect the above-mentioned properties. The purpose
of this study was also to evaluate whether birch sap,
so popular lately, can be a valuable natural beverage.
Materials and Methods
Sample collection
The study was conducted in three sites that dif-
fered in terms of the type of habitats: industrial area
(steel mill, Ostrowiec), high traffic area (Rzeszów) and
suburban area (Zalesie). Birch sap was collected from
4-5 randomly chosen individuals of B. pendula and B.
pubescens. Soil samples were taken from one soil layer
(0-20 cm) close the trees from which sap were harvest-
ed. The sampling was carried out at the end of March
and the beginning of April 2015. At a height of 30 cm
of the trunk, small 8 mm diameter holes were drilled,
then, a plastic pipe (15 cm long and 8 mm in diameter)
was put into the hole. Underneath each pipe, a sterile
plastic tube was placed (volume of 50 mL). The tubes
were closed after collecting the sap and then filtered
with 0.45 µm filters and frozen at -80oC till analysis.
Chemical analysis
Antioxidant activities
Antioxidant activities were determined by two
methods: FRAP and ABTS. For ABTS determination,
method of Re et al. (1996) was used. The results were
expressed as µmoles of Trolox per 1L of birch sap.
A manual assay of ferric reducing/antioxidant
power (FRAP) was used based upon the methodolo-
gy of Benzie and Strain (1999). A standard Trolox so-
lution was used for the calibration curve and the re-
sults were expressed as µmoles of Trolox equivalent
per 1L of birch sap.
Total polyphenol content was measured using the
Folin-Ciocalteu colorimetric method (Singleton and
Rossi 1965). The results were expressed as mg of gal-
lic acid equivalents (GAE) per 1L of birch sap.
Microbiological assay with Enterococcus hirae
ATCC 8043 was used for folic acid determination
according to Difco & BBL Manual, 2nd Edition.
E. hirae was added to the medium used for this anal-
ysis (Folic Acid Assay Medium  FAAM). E. hirae
cannot grow on FAAM without addition of external
folic acid. The addition of folic acid in specified in-
creasing concentrations gives a growth response that
can be measured turbidimetrically. Briefly, night cul-
ture of E. hirae (previously washed three times in order
to remove all residues of folic acid from the medium)
was used for inoculation of FAAM medium with in-
creasing concentrations of folic acid (0-10 ng/10 ml for
calibration curve) or with different concentrations of
analyzed birch saps. After 24 h incubation at 37oC,
bacterial growth was determined turbidimetrically at
OD 660 nm. Concentration of folic acid was calculat-
ed from the calibration curve.
Nutrients determination
Sugars (glucose, fructose, sucrose) were deter-
mined reflectometrically according to the appropriate
manuals of Merck Reflectoquant®. Results were ex-
pressed as g of sugar per 1L of birch sap. Proteins were
determined according to the Lowry method (Lowry et
al. 1951). For the calibration curve, bovine serum albu-
min was used. Results were expressed as mg of protein
in 1L of birch sap. Total calories were calculated as a
sum of calories from sugars and proteins, where pro-
teins possess 4 kcalg-1 and sugars 3.8 kcalg-1.
Minerals detection
Mineral elements were analyzed by an inducted
coupled plasma optical emission spectrometer (ICP-
OES), ThermoiCAP Dual 6500 (USA). Each time, the
dilution of 1 mL volume of birch sap filled up the tube
to 10 mL with deionised water was performed. For each
of the elements, 3-point calibration curves were cre-
ated. Selection of appropriate length measuring line
has been validated by method of standard additions
in amount of 10 ppb to 100 ppb give the recovery on
selected lines above 98.5% for each of the elements.
Soil samples were heated at 100oC till constant
weight. Then 0.2 g of soil samples were filled up with
6 mL of 40 % HCl + 2 mL of HNO3. Microwave miner-
alization procedure with Milstone Ethos One Micro-
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2017, Vol. 23, No. 2 (45)

wave Digestion System was used. After mineralization,
samples were filled up to 50 mL with demi water and
used for mineral elements detection. Mineral elements
were analyzed with the aid of inducted coupled plas-
ma optical emission spectrometer (ICP-OES), Ther-
moiCAP Dual 6500 (USA). Results were expressed as
g per kg of dry soil sample.
Data analysis
The comparison of the means of the analyzed
parameters of two species was tested by the paramet-
ric Students T-test. ANOVA or Kruskall-Wallis test
(nonparametric) with appropriate post-hoc tests (Tuk-
eya or Dunna, respectively) were applied to compare
the means from three sites. The type of statistical test
was chosen after analysis of the data distribution using
Shapiro-Wilk test. The statistical hypotheses were
tested with a£0.05.
Results
Antioxidant activities
The in vitro antioxidant effect of the investigat-
ed extracts was evaluated by the ABTS assay as a
capability of ABTS·+, a compound possessing and
antiradical activity, to scavenge free radicals and by
the FRAP assay as a capability of antioxidants to re-
duce Fe(III) to Fe(II) (Liaudanskas et al. 2014). The
results obtained from the study of the antioxidant
properties are given in Table 1. It was shown that birch
saps from Ostrowiec contained the highest levels of
antioxidants in comparison with saps from Zalesie and
Rzeszow. Antioxidant activities were higher by about
45-80% for the FRAP and 54-64% for the ABTS meth-
ods. Analysis of the variance allowed us to prove that
there are statistically significant differences in antioxi-
dant activities between different localities of silver
birch trees. Antioxidant properties detected by FRAP
and ABTS methods are different between saps from
the industrial area (Ostrowiec) and the traffic area
(Rzeszow), and also between the industrial region
(Ostrowiec) and the suburban region (Zalesie). There
are slightly but not significant differences in antioxi-
dant activities between saps from Zalesie and Rzeszów
(Table 1). Antioxidant properties were higher for sil-
ver birch sap, but the differences were not statistical-
ly significant.
Phenolic compounds
The total phenolic content of the birch saps was
estimated by using the Folin-Ciocalteu reagent. Table 1
summarizes that average concentration of total phe-
nolic compounds in birch saps varied widely ranging
from 35.41 mg GAE·L-1 for silver birch from Zalesie to
55.15 mg GAEL-1for silver birch sap from Ostrowiec.
When comparing the concentration of phenolic com-
pounds depending on the locality, where sap was tak-
en, there have been revealed statistically significant
differences between the industrial region, Ostrowiec,
and the suburban region, Zalesie, which are in corre-
lation with antioxidant activities (Table 1). Authors did
not detect statistically significant differences in phe-
nolic compounds concentration between the birch
species.
Folic acid concentration
Folic acid is one of the vitamins, which also pos-
sess antioxidant activities. The highest values were
obtained from silver birch sap from Ostrowiec, and
values subsequently decreased in the following order:
silver birch  Zalesie < silver birch  Rzeszow < downy
birch (Table 1).
Nutrients
Among sugars, which were analyzed, the lowest
glucose and fructose concentrations were detected for
downy birch sap and the highest ones for silver birch
sap from Ostrowiec. Differences between glucose con-
centrations are from 36% to 55%, and for fructose
concentrations from 24% to 60%. The concentration
of sucrose is also the lowest for the downy birch sap.
Saps from silver birch trees localized in Rzeszow and
Ostrowiec were the same in terms of the sucrose con-
tent and the highest sucrose concentration was de-
tected for sap from Zalesie. However, it is worth to
state that the standard deviation in these samples is
very high. On the other hand, the highest protein
concentration was detected for silver birch sap but
differences between the protein concentrations are
quite low, around 6  12% (Table 1). Comparing the
saps of the two birch species, it can be stated that
statistically significant differences were detected only
in the content of glucose and sucrose (Students T-
test; p=0.0014; Table 1). Birch sap is a low-calorie
diet beverage. Calorie content of silver birch sap from
suburban and industrial sites was in the range from
29.95 to 47.68 kcalL-1, respectively, and the average
calorie content for downy birch sap is 39.45 kcal·L-1.
Minerals in the birch sap
Of all the investigated minerals, calcium present-
ed the highest content especially in the traffic area,
where its concentration was significantly higher than
at the other sites (above 75%). In the industrial and
suburban areas, its concentrations were similar oscil-
lating around 165 mg per litre. Also, a quite high po-
tassium content was noted. Its concentrations ranged
on average from 100 to 180mgL-1. Authors stated sig-
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ISSN 2029-9230
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2017, Vol. 23, No. 2 (45)

nificant differences in the potassium concentration at
sites with the lowest content in the suburban area.
Concentrations of manganese and zinc in silver birch
sap were similar and on average ranged from 2 to
4mgL-1. It was stated that concentrations of certain
microelements depended on the habitats. Mean con-
centration of sodium was the highest in the industrial
area, and of iron and phosphorus in the traffic one.
Copper concentrations differed at each of the habitats
(Table 2). Silver and downy birches differed in phos-
phorus and iron content, which were higher for the
latter species (Students T-test; 0.046, p=0.0049, re-
spectively; Table 2). In downy birch sap, sodium was
not detected. Concentrations of cadmium, chromium,
lead, nickel and aluminium were below their levels of
determination.
Minerals in soil
It can be stated that soil samples from Ostrowiec
differs from soil samples from other places containing
higher concentrations of some elements. They are richer
in Ca, Zn, P, Ca, Cu, Fe and Na (Table 3). Among heavy
metals, Pb, Cd and Cr concentrations are higher in soil
from Ostrowiec too. Ni and Al concentrations are sim-
ilar in all types of soils varying from 0.01 to 0.024 and
from 4.1 to 6.38gkg-1, respectively. Pb concentration
is 5-11 times higher than in soils from the traffic area,
and more than 30 times higher than in soil from the
suburban area. Cd concentration is 20 times higher than
in suburban area and one soil from the traffic area was
around 10 times higher than in the soil from other traf-
fic area. Cr concentration is 1.5 times higher than in the
traffic area, and 3.5 times higher than in the suburban
area. Heavy metals (HM) like Ni, Pb, Cd, Cr, Al and Zn
were determined in all analysed soil samples. But it can
be stated that in most cases HM concentrations in soil
Table 1. Mean concentrations of chosen parameters of anti-
oxidants and nutrients for Zalesie (Z), Rzeszów (Ra  B. pendula,
Rb  B. pubescens) and Ostrowiec (O)
Species Sites Ca
(mg·L-1)
K
(mg·L-1)
Mg
(mg·L-1)
Mean ± SD
Z
169.27 0±68.987a 107.366±58.401
a 18.635±11.538a
B. pendula Ra 212.767±16.238b 174.569±53.820b
25.307±4.610 7a
O 162.587±29.356a 179.136±60.641
b
31.196±12.646b
B. pubescens Rb 217.874±67.501 149 .087±43.746 24.9627±6.642
Species Sites Zn
(mg·L-1)
P
(mg·L-1)
Na
(mg·L-1)
Mean ± SD
Z
2.967±0.995a 7.008±2.054a 0.266±0.359a
B. pendula Ra 4.115±1.72a 23.522±7.447b
0.158±0.279a
O 3.243±0.775 a 19.916±6.124b
1.974±1.689
b
B. pubescens Rb 4.498±1.608 a 34.992±8.44* nd
Species Sites Cu
(µg·L-1)
Fe
(mg·L-1)
Mn
(mg·L-1)
Mean ± SD
Z
0.048±0.019a 0. 198±0.042a 2.955±2.363
B. pendula Ra 0. 099±0.015b 0.249±0.049b 4.092±6.977
O 0.138±0.021c 0.203±0.034a 1.929±1.910
B. pubescens Rb 0.089±0.020 0.304±0.089* 7.923±3.61
Notes: (a, b and c mark statistically significant differences
between the sites according to ANOVA or Kruskal-Wallis tests
and post hoc tests, a£0.05; * the differences between spe-
cies according to Students t-test with a£0.05; nd stands for
not detected.
Notes: (a, b and c mark statistically significant differences
between the sites according to ANOVA or Kruskal-Wallis tests
and post hoc tests, a£0.05; * the statistically significant dif-
ferences between species according to Students t-test (with
a£0.05).
Species Sites FRAP
Trolox
(µmoles·L-1)
ABTS
Trolox
(µmoles·L-1)
Phenolic
compounds
Gall ic acid
(
m
g
·L-1
)
Folic acid
(µg·L-1)
Mean ± SD
Z 41.10±18.89
a 313.03 ±67.95a 35 .41±19.82
a 5.79 ±2.49ab
B. pendula Ra 49 .45±8.38a 30 5.92±60.18a 40.3 9±9.91
ab 4.39±1.04
a
O 71.95±15.51
b 481.36±73.83b
55.15±15.89
b 7.10±2.43
b
B. pubescens Rb 40.00±14.62 294.32±46.44 38 .13±7.26 3.93 ±1.83
Species Sites Glucose
(g·L-1
)
Fruct os e
(g·L-1
)
Sucrose
(g·L-1
)
Proteins
(g·L-1
)
Mean ± SD
Z 5.23±3. 47 5.36 ±2.95 0.63 ±0.71 0.272±0.105
B. pendula Ra 4. 72±2.09 4. 82±1.82 0. 28±0.12 0.272±0.117
O 5.38 ±1.11 6.23±3. 11 0. 28±0.19 0.287±0.130
B. pubescens Rb 3.46±0. 61 3.88±0. 38 0. 014±0.023* 0. 307±0.073
Table 2. Mean concentrations of chosen minerals for Zale-
sie (Z), Rzeszów (Ra  B. pendula ,Rb  B. pubescens ) and Ostro-
wiec (O)
Sites Ca
(g·kg-1
)
K
(g·kg-1
)
Mg
(g·kg-1
)
Zn
(g·kg-1
)
P
(g·kg-1
)
Mean ± SD
Z 1.234±0.0 14a 0.801±0.014a 1.318±0.014a 0.026±0.0 01a 0.246±0.003 a
Ra 4.842±0.0 66b 3.609±0. 029b
3.418±0.014b 0. 0797±0.000b
0.607±0.014b
O 12.284±0.014c 1.220±0.0 14c 2.635 ±0.0 43c 0.80 6±0.0 14c 8.09 1±0.0 52c
Rb 1.600±0.0 54d 2 .309±0.0 52d
2.51 0±0.0 25d 0 .056 ±0.001d
0.63 2± 0.014b
Sites Na
(g·kg-1
)
Cu
(g·kg-1)
Fe
(g·kg-1
)
Mn
(g·kg -1)
S
(g·kg-1
)
Mean ± SD
Z 0 0.00 7±0.0 00a 7.40 4± 0.052a 0 .2696 ±0.001a 0 .059 ±0.0 01a
Ra 0.09 7±0.0 03a 0.02 3±0.0 03b
17.2 29±0.0 76b
0.38 2±0.0 14b 0.287 ±0.0 01b
O 0.08 8±0.0 04b 0. 063±0.0 01c 22.463± 0.413c 0.479 ±0.0 09c 0.81 2±0.0 14c
Rb 0.04 1±0.004 c 0.03 5±0.001d
13.2 38±0.0 90d
0.33 8±0.0 13d 0.158± 0.001d
Sites Ni
(g·kg-1
)
Pb
(g·kg-1)
Cd
(g·kg-1
)
Cr
(g·kg -1)
Al
(g·kg-1
)
Mean ± SD
Z 0.01 0±0.0 00a 0 .004± 0.000a 0 .0000 9±0.0 00a 0 .015±0.001a 4 .100± 0.025a
Ra 0.02 4±0.0 01b 0.029± 0.001b
0.00 02±0 .052b
0.03 7±0.0 00b 6.375±0.025b
O 0.01 6±0.0 01c
0.13 8±0.0 01c 0.0019 3±0.00 0c 0.053 ±0.0 01c 5.35 0±0.0 25c
Rb 0.01 8±00 01c 0.012±0.0 00d
0.00 008 ±0.00 0a 0.03 0±0.0 01d 6.300± 0.05 b
Notes: (a, b and c mark statistically significant differences
between the sites according to ANOVA or Kruskal-Wallis tests
and post hoc tests with a£0.05; * the statistically significant
differences between species according to Students t-test with
a£0.05.
Table 3. Mean concentration of chosen minerals in soil from
Zalesie (Z), Rzeszów (Ra  B. pendula ,Rb  B. pubescens ) and Ostro-
wiec (O)
D. GRABEK-LEJKO ET AL.
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THE BIOACTIVE AND MINERAL COMPOUNDS IN BIRCH SAP /.../
ISSN 2029-9230
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2017, Vol. 23, No. 2 (45)

from the industrial area (Ostrowiec) were higher than
from ones of the other localities.
Discussion
Nowadays, there is a tremendous resurgence in
the interest and use of natural healthy products, foods,
medicinal plants etc. According to the World Health
Organization (WHO), as many as 80% of the worlds
people depend on traditional medicine for their primary
health-care needs (WHO 1993, Ðkrovánková et al.
2012). The number of consumers interested in healthy
food continues to grow, which corresponds with an
increasing number of health-food and specialty stores,
in which different healthy products are available
(Briskin 2000). Birch sap is an example of such a prod-
uct that is becoming more and more popular in Poland.
It is available in special healthy food stores but late-
ly also in supermarkets, the advertising campaign was
extended in the popular media, and moreover, there are
more and more distributors and producers of this prod-
uct.
The present study quantitatively determined the
concentration of bioactive and nutrition compounds as
well as mineral substances in saps obtained from two
species of birch trees, B. pendula (silver birch) and B.
pubescens (downy birch). We have attempted to find
out if there are any differences in these parameters
depending on the birch species and localities (between
the traffic, suburban and industrial areas).
According to these studies, authors can easily
detect that antioxidant properties of saps from the
industrial region are significantly higher than those
from the traffic and suburban areas both for FRAP and
ABTS methods, respectively. It is known that differ-
ent stress factors, environmental pollution etc. caus-
ing oxidative stress are connected with reactive oxy-
gen species (ROS) formation. Living organisms like
plants possess several antioxidative defense systems
to scavenge toxic-free radicals in order to protect them-
selves from the oxidant stress (Zeneli et al. 2013). It
was reported that the tolerance of plants for oxidative
stressing conditions may be explained by the enhanced
activity of antioxidative enzymes preventing cell and
tissue damage (Shi et al. 2006). Higher antioxidant
properties of saps from the industrial region may have
reflected higher environmental stressing conditions in
comparison with saps from other sites (Krishnaveni
2013). Moreover, it was reported that antioxidant prop-
erties may depend on the species or even individu-
als. Some plants, growing near cement factory and
exposed to cement dust pollution, exhibited higher
antioxidant properties than control plants, but other
species have a lower defense system against cement
dust pollution and lower antioxidant potential than
appropriate control plants (Mutlu et al. 2009). There-
fore, higher antioxidant capacities of birch sap from
the industrial area can be explained as a high toler-
ance of birch to environmental pollution, manifested
by an increased content of antioxidants protecting the
plant against different environmental stresses. There-
fore, in theory, variations in antioxidant responses
throughout the life cycle occur, making the plant more
or less susceptible to seasonal variations in diverse
environmental stressors.
Variations in the levels of antioxidants may also
occur during the aging of the plant (Ferreira and Do-
mingos 2012). The authors chose the trees randomly
so this can be an explanation for large differences in
maximum and minimum values of these parameters at
one location. It is difficult to compare results obtained
in our study to others because there is little informa-
tion about antioxidants in birch saps or researchers
used different methods to estimate the antioxidant
capacity with different standards, incubation time and
concentrations. Kûka et al. (2013) detected the anti-
oxidant concentration of Latvian birch saps at 0.35
mgL-1 of quercetin equivalent.
It is known that the concentrations of phenolic
compounds in many plants are strictly correlated with
their antioxidant properties (Piluzza and Bullitta 2011,
Jeong et al. 2013). Observed differences between the
phenolic content in analyzed saps showed that phe-
nolic compounds were important antioxidant compo-
nents. Concentration of folic acid along with antioxi-
dant properties (Joshi et al. 2001) is much higher in
saps from the industrial region, which means that in
all methods used for antioxidant detection, authors
observed statistically significant difference in their
concentration in saps from the industrial region com-
pared with saps from the traffic and suburban areas.
The formation and level of antioxidants may be
seasonality marked in response to changes in the
environmental conditions. This is plausible because
the seasonality is reflected in solar irradiation, pho-
toperiod, temperature, relative humidity and actions of
other meteorological factors. Some authors also ob-
served that antioxidants concentration can be a re-
sponse to the meteorological characteristics of each
season of the year (Ferreira and Domingos 2012). The
differences in the antioxidant concentration between
localities can be explained by some differences in the
course of weather in 2015 during flow season in dif-
ferent regions of Poland as well as the microclimate
(Meteoblue Weather 2016).
Analyzing the sugar concentration, authors ob-
served that the saps contained mainly fructose and glu-
cose, however, sucrose was also found in lower amounts.
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Sugar proportions were similar to those found in north-
ern Europe and in Poland (Kûka et al. 2013, Ùuczaj et al.
2014). Sugar, protein and mineral concentrations obtained
by other authors were shown in Table 4.
These results are also similar to those detected
by Korean researchers for white birch sap (Jeong et
al. 2012). They detected that its sugar content varied
from 3.6 to 4.3gL-1 and from 4.9 to 6.6gL-1 for glu-
cose and fructose, respectively. In results presented
in this paper, glucose concentration was slightly high-
er for silver birch sap from Zalesie and Ostrowiec.
Polish silver birch sap contains more glucose and fruc-
tose than birch sap produced in Lithuania and in Fin-
land (Kûka et al. 2013). Glucose and fructose concen-
trations in downy birch sap is approximately 30% low-
er than in saps from Polish and Latvian silver birch
(Table 4). In contrast to these results, Ùuczaj et al.
(2014) did not detect significant differences in sugar
concentrations between silver birch and downy birch
saps. It can be explained by the fact that the amount
of sugars in tree saps depends on many parameters.
The tree sap sugar concentrations can be affected by
the time of day, stage of flow cycle (beginning/end of
the flow), tree size, age and soil fertility, basal area of
ray issue and weather conditions in the year, or even
shifts in gas contents in the atmosphere.
Sucrose concentration in white birch sap detect-
ed by Jeong et al. (2013) was 0.07 gL-1. For these sap,
sucrose concentration was at least four times higher
than for silver birch sap localized in Rzeszow and
Ostrowiec, and almost ten times higher than for sap
from Zalesie. However, authors observed a great var-
iability between individuals. On the other hand, su-
crose concentration for downy birch was five times
lower than those detected by Jeong et al. (2013)
(Table 4). For Latvian birch, the sucrose concentra-
tion was about 0.58 gL-1, which is twice higher than
for B. pendula from the industrial and traffic areas and
slightly lower  around 10%  than for sap from sub-
urban area (Kûka et al. 2013). Statistically significant
differences in glucose and sucrose concentrations be-
tween species are attributed to species factors.
Protein concentrations in our saps are at least twice
higher than those detected for Lithuanian birch saps
(Kûka et al. 2013). Japanese researchers also detected
a very low protein concentration for saps from white
and silver birches at a level of 15-35 mgL-1 depending
on the harvesting time (Jiang et al. 2001) (Table 4). As
Ùuczaj et al. (2014) said, relatively high values of sug-
ars in Polish saps suggest that Poland may be a suita-
ble place for developing the tree sugar industry.
Birch sap contains over a dozen minerals (Harju
and Hylden 1990). In many scientific works, the au-
thors indicated that among minerals copper reached
Parameter Object Analytical result s Reference
Glucose
(g·L -1
)
B. pendula 3.6 to 4.3 Jeong et al. (2012)
B. pendula 9.3± 3.9 Ùuczaj et al. (2014)
B. pendula 3.55-4.96 Bilek et al.
(
2015b
)
B.
p
endula 4.46±0.04 Kûka et al.
(
2013
)
B. pubescens 1.99-3.016 Bilek et al. (2015b)
B. pubescens 9.6±2.9 Ùuczaj et al. (2014)
B. platyphylla var.
japonica
2.5 Jeong et al. (2013)
Fructo se
(g·L -1
)
B. pendula 4.9 to 6.6 Jeong et al. (2012)
B. pendula 5.39± 0.05 Kûka et al. (2013)
B. pendula 12.1± 4.9 Ùucza
j
et al.
(
2014
)
B.
p
endula 4.03-4.77 Bilek et al.
(
2015b
)
B. pubescens 13.5±3.3 Ùuczaj et al. (2014)
B. pubescens 1.83-2.77 Bilek et al. (2015b)
B. platyphylla var.
japonica
3.3 Jeong et al. (2013)
Sucrose
(g·L -1
)
B. pendula 0.07 Jeong et al. (2013)
B. pendula 0-1.509 Bilek et al. (2 015b)
B. pendula 0.58± 0.01 Kûka et al. (2013)
B. pendula 3.2± 2.4 Ùucza
j
et al.
(
2014
)
B. pubescens 3.1±1.4 Ùuczaj et al. (2014)
Protein
(mg·L -1
)
B. pendula 127±2 Kûka et al. (2013)
B. platyphylla var.
japonica
15-35 Jiang et al. (2001)
B. verruco sa 15-28 Jiang et al. (2001)
Ca
(mg·L -1
)
B. pendula 41.0-53.3 Kûka et al. (2013)
B.pendula 5.52 -17.28 Bilek et al. (2015)
B.
p
ubescens 15.12±4.74 Bilek et al.
(
2015
)
B. platyphylla var.
japonica
25.82±0.12 Jeong et al. (2013)
Betula sp. 42  150 Vincçvièa-Gaile (2014)
Cu
(mg·L -1
)
B.
p
endula 0.15-0.39 Bilek et al.
(
2015
)
B. pendula 0-0.04 Kûka et al. (2013)
B. pubescens 0.48±0.42 Bilek et al. (2015)
B. platyphylla var.
japonica
0.82±0.10 Jeong et al. (2013)
Betula sp. 0.02-0.03 Vincçvièa -Gaile (2014)
Fe
(mg·L -1
)
B. pendula 0-0.1 Kûka et al. (2013)
B. platyphylla var.
japonica
0.61±0.09 Jeong et al. (2013)
Betula sp. 0.05-0.11 Vincçvièa-Gaile (2014)
K
(mg·L -1
)
B. pendula 10.56-23.76 Bilek et al. (2015)
B. pendula 41.1-66.4 Kûka et al. (2013)
B.
p
ubescens 18.08±18.85 Bilek et al.
(
2015
)
B. platyphylla var.
japonica
30.10±4.81 eong et al. (2013)
Betula sp. 54  142 Vincçvièa-Gaile (2014)
Mg
(mg·L -1
)
B. pendula 4.42-14.36 Bilek et al. (2015)
B. pubescens 13.82±5.55 Bilek et al. (2015)
B. platyphylla var.
japonica
11.90±0.15 Jeong et al. (2013)
Betula sp. 0 Vincçvièa-Gaile (2014)
Mn
(mg·L -1
)
B. pendula 0.5-0.52 Kûka et al. (2013)
B. platyphylla var.
japonica
2.36±0.02 Jeong et al. (2013)
Betula sp. 0.11-6.16 Vin cçvièa-Gaile (2014)
Na
(
m
g
·L-1
)
B. pendula 0.56-0.59 Bile k et al. (2015)
B.
p
ubescens 0.55±0.62 Bilek et al.
(
2015
)
B. platyphylla var.
j
a
p
onica
7.51±0.36 Jeong et al. (2013)
Betula sp. 0 Vincçvièa-Gaile (20 14)
Ni
(mg·L -1)
B. pendula 0-0.03 Kûka et al. (2013)
Betula sp. 0.02-0.16 Vincçvièa-Gaile (2014)
Zn
(mg·L -1)
B. pendula 0.88-1 .85 Bilek et al. (2015)
B. pubescens 1.29±0.17 Bilek et al. (2015)
B. platyphylla var.
j
a
p
onica
3.82±0.47 Jeong et al. (2013)
Betula sp. 0.9-4.96 Vincçvièa-G aile (2014)
P (mg·L -1) Betula sp. 3 - 41 Vincçvièa-Gaile (2014)
S (mg·L -1) Betula sp. 5  12 Vincçvièa-Gaile (2014)
Cr (mg·L
-1) Betula sp. 0.02 Vincçvièa-Gaile (2014)
Co (mg· L-1) Betula sp. 0.05 Vincçvièa-G aile (2014)
Table 4. Concentration of sugars, proteins and selected mine-
rals in birch saps
Jeong et al. (2013)
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ISSN 2029-9230
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2017, Vol. 23, No. 2 (45)

the lowest concentrations, whereas calcium and po-
tassium reached the highest ones (Kûka et al. 2013,
Vincçvièa-Gaile 2014, Bilek et al. 2015a) (Table 4). Harju
and Hylden (1990) noted the concentrations of man-
ganese, phosphorus and zinc exceeded 1 mgL-1. Pre-
sented results are in accordance with them, however,
we observed the great variability among individual
trees as well as the sites. It concerned mainly sodi-
um, what was also detected by Bilek et al. (2015a).
Bilek et al. (2015a) compared the mineral com-
pounds of the sap with the recommended daily allow-
ance for adults. According to their results, one liter
of silver birch sap covers up to 40% of daily copper
requirements, zinc up to 17%, calcium up to 2%, mag-
nesium up to 3-4% and sodium up to 0.04%. The
authors obtained different results such as about 11%,
30%, 18%, 8% and 0.05%, respectively.
The high variability could be affected by environ-
mental and anthropogenic factors. In polluted areas,
concentrations of certain minerals in plants increase
(Vincçvièa-Gaile 2014). The authors noted that the
highest iron and phosphorus concentrations were in
the sap harvested from the traffic and industrial sites.
High concentrations of heavy metals (HM) may neg-
atively affect living organisms, the ecosystems and
human health. HMs presented in soils may be trans-
ported through the food chain to the human body and
have a significant toxic effect to people (Butkus and
Baltrënaitë 2007, Yan et al. 2012). Harju and Hylden
(1990) found increased concentrations of Pb, Zn, Ag
and Cd in birch sap collected in polymetallic damps
in south western Finland. Generally, in study areas the
concentration of minerals was higher in soil collected
near steel mill (Ostrowiec) and the lowest ones in soil
from suburban area (Zalesie) but authors did not de-
tect any connection between mineral concentrations
in soils and in saps. Among HMs only a few ones were
detected in saps. These results confirm that transport
of many HMs from soil to plant is not very active
(Kandziora-Ciupa et al. 2015). Lead is characterized by
poor bioavailability and therefore it was not found in
saps. Also very toxic cadmium was not transported
from soils to saps. Copper and zinc as trace elements
are essential for proper metabolism, growth and de-
velopment of plants, but in the highest concentrations
are toxic (Wierzbicka 2015). Authors noted that in soil
these elements were presented but their concentrations
in the saps were low. These results are very impor-
tant for potential consumer because, regardless of the
heavy metal soil contamination, birch sap is resistant
to toxic minerals.
Conclusion
Taking into account its chemical composition,
birch sap should be considered as a low-calorie diet
supplement, a good substitute for water: medium and
high mineralized, which should contain at least 150 mg
per litre of macronutrients like Ca, K and Mg. In re-
spect of minerals, antioxidant and nutrient properties
the downy birch sap is just as valuable as the sap of
silver birch. Variation in chemical compounds may be
caused by the type of habitats and inter-individual
variability. It seems that birch sap is quite resistant
to heavy metals present in soil. Heavy metals concen-
trations in soil, as well as other environmental stress-
es such as pollutants of traffic origin may cause high-
er antioxidant activity of birch sap. When preparing
to sap harvesting, the potential soil and air pollution
in sampling site should be taken into account.
Acknowledgement
The work was partly supported by Cross-border
Cooperation Programme Poland-Belarus-Ukraine
2007-2013, IPBU.03.01.00-18-452/11-00 and by the
Polish Ministry of Science and Higher Education (No
3020/PBU/0755/11/13/2014/2). Responsibility for the
content of this publication lies solely with the authors
and cannot, under any circumstances, be considered to
reflect the position of the European Union in any way.
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Accepted 30 September 2016
°
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ISSN 2029-9230
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2017, Vol. 23, No. 2 (45)