Vol.4, No.5B, 130-135 (2013) Agricultural Sciences
Mulberry fruit as an antioxidant component in muesli
Joanna Kobus-Cisowska, Anna Gramza-Michalowska, Dominik Kmiecik, Ewa Flaczyk,
Józef Korczak
Faculty of Food Science and Nutrition, Poznan University of Life Sciences, 31 Wojska Polskiego Str., 60-624 Poznan, Poland;
*Corresponding Author: joannak@up.poznan.pl
Received 2013
The aim of the study was to develop the tech-
nology of muesli via analyzing the addition of
white mulberry fruit. The first step involved the
selection of ingredients from bioactive com-
pounds. Next, the technology of production was
developed. Then, the antioxidant activity of new
muesli with potentially pro-health model sys-
tems was estimated. Muesli was characterized in
terms of its basic nutritional value, and antioxi-
dant potential. The ability to inactivate DPPH
and ABTS radicals was estimated. In addition,
the amount of fat in muesli was calculated. As
part of this calculation, fatty acid composition
and content of primary and secondary oxidation
products were ascertained. The last stage of the
project included sensory analysis of the resul-
tant products. Our studies showed that the new
product-muesli had high nutritional value, high
antioxidant potential and a positive fatty acid
composition. And sensory analysis showed that
the product was attractive.
Keywords: Mulberry; Morus Alba; Muesli;
Antioxidant Properties; Bioactive Food
There is an increasing awareness of diseases associ-
ated with diet. Numerous analyses have shown that foods
containing phytochemicals with antioxidant compounds
have a strong protective effect against major diseases; for
example cardiovascular diseases, diabetes, cancer, obesity
and many others [1-3]. Most antioxidant compounds in
food are derived from different plants and belong to vari-
ous classes of compounds with a wide variety of physical
and chemical properties – carotenoids, dietary glutathione
polyphenols, and vitamins. Moreover, these compounds
also play a significant role in the assurance of high quality
food, including mainly fat containing food, by the inhibi-
tion of oxidative changes to this fat. Lipid oxidation is a
highly deteriorative process in foods, which lead first of
all to unacceptable properties for the customer and most
importantly a loss in nutritional value [4-7].
The mechanism of polyphenol activity is highly differ-
entiated. They might act as reducing substances, com-
pounds blocking free radicals, chelating metal ions, cata-
lysts of oxidation reaction, inhibitors of the activity of
enzymes contributing to free radical creation, e.g. xan-
thine oxidase, lipoxygenases or protein kinase. In addi-
tion, they may reduce reactive oxygen species to more
stable forms [7-9].
The most commonly grown species in the Morus ge-
nus are white mulberry, black mulberry, and red mul-
berry [10,11]. Mulberries (Morus alba) have long been
used in traditional medicine to improve eyesight, lower
blood pressure, prevent diabetes, protect the liver,
strengthen joint and treat fever. Fruits, leaves, sprouts as
well as bark are currently used in production processes,
and various forms of final products, including syrups,
jams, ice-cream, vinegar or alcohol, are produced from
them [11,12]. As may be concluded from numerous re-
ports, the fruits of the white mulberry (Morus alba L.),
due to their characteristic composition and properties,
may additionally profitably affect the human organism.
Mulberry fruits are rich in organic acids such as malic
acid, citric acid, and tartaric acid [3,10,12]. This fruit
contains essential fatty acids, as well as vitamins and
polyphenols which are effective antioxidants [11].
The present study aimed to develop a technology for
producing muesli with the fruit of the white mulberry.
This object was achieved by:
• Selection of materials containing potentially bioac-
tive compounds,
• Development of production technology by detailing
the percentage of each fraction,
• Evaluation of the antioxidant activity of the resulting
muesli with potentially pro-health model systems.
2.1. Material
Ingredients used for muesli preparation were purchased
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J. Kobus-Cisowska et al. / Agricultural Sciences 4 (2013) 1 30-135 131
in local stores, with a minimum three months of shelf- life.
These included: oatmeal (Kupiec Sp. z o.o., Krzymów,
Poland), linseed (Sante, Warsaw, Poland), granulated oat
bran (Sante, Warsaw, Poland), dried appled (Paula,
Kalisz, Poland), dried cranberry (Bakalland, Warsaw,
Poland), dried mulberry fruits (Bio Planet, Leszno, Po-
All solvents were of analytical grade unless otherwise
specified. 2,2-Diphenyl-1-picrylhydrazyl. (DPPH.), 6-
hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid
(Trolox), and Folin-Ciocalteau reagent were purchased
from Sigma-Aldrich (St. Louis, MO, USA). The other
chemicals were obtained from Merck (Darmstadt, Ger-
many) and POCH (Gliwice, Poland).
2.2. Muesli Preparation
A base muesli formulation, taken from the literature [9]
and slightly modified was used as a reference and was
prepared in the laboratory (sample A). Muesli samples
(with apple and cranberry - sample B and with an addi-
tion of apple, cranberry and mulberry fruit-sample C)
were prepared according to Table 1.
2.3. Chemical Characteristics of Muesli:
Protein, Total Dry Matter, Lipids, Ash,
Fatty Acid Composition
All analyses were performed on these 3 samples in 3
replications according to method AOAC [13]. The mois-
ture of samples was determined by drying at 103 ± 2℃
until they reached a constant weight. Protein content was
determined by the Kjejdal method (N × 6.25), in Kjeltec
2200 (Foss Tecator, Sweden). Fat content was deter-
mined using the method of multiple constant extraction
with petroleum ether, which was next evaporated, and
the weighing method was used in the fat content exami-
nation. A Soxtec HT6 apparatus manufactured by Foss
Tecator (Sweden) was used for the extraction. Ash con-
tent was examined by incineration in a muffle furnace –
Naberterm S 27- at a temperature of 535℃, with air ac-
Table 1. Composition of muesli flakes.
Ingredients: sample A: sample B: sample C:
oatmeal 300 g 300 g 300 g
oat bran (granulated) 90 g 90 g 90 g
linseed 60 g 60 g 60 g
dried cranberry - 60 g 60 g
dried apple - 60 g 60 g
dried mulberry - - 110 g
The percentage composition of fatty acids was deter-
mined using a gas chromatograph with an FID detector
(Agilent Technologies 7820A GC) according to method
described in PN-EN ISO [14]. The method involved dis-
solution of a fat sample with hexane, and its further
trans-esterification using sodium methanol solution.
2.4. Antioxidant Activity
The of total phenolic content (TPC) in muesli was de-
termined by visible spectrophotometry based on a col-
orimetric oxidation/reduction reaction according to Cheung
et al. [15]. Ferulic acid was the standard employed in this
work. The absorbance of the sample was measured at λ =
725 nm using a SPECORD® 40 (Analytik Jena AG,
Germany). Based on the construction of a standard curve,
TPC data for the preparations from muesli were ex-
pressed as mg ferulic acid equivalents/g dry extract.
The free-radical-scavenging potentials of muesli were
tested in a methanolic (80%) and water solution of DPPH
as described by Amarowicz et al. [16]. The extent of
discoloration of the solution indicated the scavenging
efficacy of the added substance. Absorbance was meas-
ured at λ = 517 nm (SPECORD® 40, Analytik Jena).
The ability of ABTS radical cation deactivation was
examined according to the method described by Re et al.
[17]. The examination involved determination of the de-
gree of scavenging of ABTS + radical cations formed
from ABTS by oxidation with potassium persulfate. The
scavenging was measured spectrophotometrically at a
wave length of 734 nm (SPECORD® 40, Analytik Jena,
Germany). Antioxidant ability with ABTS radical cation
application was calculated per Trolox for a standard
curve, and the result was given as mg of Trolox/1 g d.m.
of an extract.
2.5. Oxidative Stability Determination
Lipid extraction
The process was run with the Folch mixture (chloro-
form: methanol 2:1 v/v). After the separation phase,
chloroform was evaporated in a vacuum evaporator and
the lipid fraction was obtained [18].
Pero xi d e val ue
The peroxide value (PV) was determined by titration
with 0.02 M sodium thiosulfate and was expressed in
meq O2/kg [19].
Anisidine value
The determination was performed based on PN-ISO
[20]. The method is based on the reaction of aldehydes
present in the sample with a p-anisidine solution in
ice-cold acetic acid and on the spectrophotometric ab-
sorbance measurement of the formed yellow complex at
a wave length of 350 nm (Metertek SP-830, Taiwan).
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2.6. Sensory Analysis
The descriptive panel comprised 20 assessors (14 fe-
male and 6 male, aged 22 to 54 y), who were students or
staff of the university.
Sensory assessment of the experimental samples of oat
muesli was conducted in the sensory laboratory fulfilling
the requirements provided in standard PN-ISO, [21].The
method of descriptive quantitative analysis, i.e. sensory
profiling, was used in the study. Qualitative determinants
of color, smell, taste and consistency were evaluated.
The intensity of each quality score was determined using
a 10cm structured linear scale with suitable margin deno-
tations. The color (beige, brown, red, orange, green, purple)
was evaluated on a scale from slightly intense to intense.
Marginal designations, i.e. imperceptible - intense, were
used for smell (fruit, cereal, foreign) and taste descriptors
(sweet, salty, bitter, cloying, fruity, vegetable, and for-
eign). Marginal designations: large, small, were used for
consistence descriptors (compactness, degree of steeping),
while crunchiness was assessed on a soft-hard scale. Also,
a general assessment of the product was performed. The
results obtained were replaced with numerical values
expressed in points.
2.7. Statistical Analysis
All analyses were made in at least three replications.
Average and standard deviation values were calculated
with the use of Microsoft Office Excel 2007 software.
Pearson’s correlation indexes were calculated with the
use of STATISTICATMPL 7.0 StatSoft. The significance
of differences between mean values was determined at p
0.05 applying the analysis of variance (ANOVA) fol-
lowed by Tukey’s multiple range test.
3.1. Chemical Characteristics of Muesli
The chemical characteristics of muesli are given in
Table 2.
The total protein content of muesli was between 12.05
(sample C with mulberry) and 16.43 (sample A - control),
respectively. Control muesli (sample A), which had the
lowest moisture content, had the highest total fat (9.81
%), followed by sample B with apple and cranberry (8.53)
and sample C with mulberry (6.93). The ash content of
the examined muesli was between 1.20% (sample A -
control) and 1.60 (sample C with mulberry), respectively.
A similar chemical composition for muesli was pre-
sented by Pernille at al. researches [4,5], where protein
and fat content was in a range up to 9% and 14%, re-
spectively. Also, the humidity of muesli in the study of
the above-mentioned authors was the same as in the pre-
sented experiment, i.e. at a level of 4% - 7%.
Fatty acid analysis showed that the muesli studied
contained six major fatty acids. Oleic acid, C18:1, was
the dominant fatty acid (34.68% - 36.31%) in all muesli
samples, followed by linoleic acid C18:2 (28.51% -
29.97%). Our results are in agreement with Pernille et al
[4], who reported that the fatty acids found at the highest
levels of muesli were oleic acid (around 48% - 49%) and
linoleic acid (20% - 31%). The examined muesli in the
study by Pernille et al. [5] also contained the highest
amount of oleic acid and linoleic acid, while stearic acid
and linolenic acid were noted at the level of 2% - 3% and
1% - 5%, respectively.
3.2. Antioxidant Activity
Antiradical activity towards ABTS and DPPH is pre-
sented in Figures 1 and 2.
Table 2. Chemical composition of muesli.
Index / Sample A B C
Protein 16.43 13.19 12.05
Fat 9.81 8.53 6.93
C 16:0 12.86 10.24 10.93
C 18:0 2.14 2.36 2.27
C18:1 34.68 36.26 36.31
C 18:2 29.94 28.51 29.97
C 18:3 20.29 22.45 20.28
C 20:1 0.11 0.17 0.24
Ash 1.20 1.50 1.60
Dry matter 93.65 92.89 92.67
Figure 1. Antiradical potential of muesli extract
measured with ABTS radicals.
Figure 2. Antiradical potential of muesli extract
measured with DPPH radicals.
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J. Kobus-Cisowska et al. / Agricultural Sciences 4 (2013) 1 30-135 133
The muesli sample with added mulberry fruit was
characterized by the highest activity towards ABTS: 7.71
mg Trolox/ g d.m. for water extract and 12.73 mg Trolox/
g d.m. for methanolic extract. Lower activity was noted
in the control sample where the values were 2.55 mg
Trolox/g d.m. for water extract, and 5.71 mg Trolox/g
d.m. for methanolic extract. In turn, the lowest activity
towards ABTS radical cation was demonstrated for the
sample with added cranberry and apple: 1.64 mg Trolox/
g d.m. for water extract, and 2.62 mg Trolox/g d.m. for
methanolic extract, respectively.
Similar results were obtained in the test with DPPH.
The highest values for antiradical activity were noted for
muesli with white mulberry. Methanolic extract demon-
strated a scavenging ability value of - 180.14 mM
Trolox/g d.m. of an extract, a 6-fold lower value for this
sample was noted in the case of water extract (31.70 mM
Trolox/g d.m. of an extract). The other two samples were
characterized by considerably lower values. Antiradical
activity for the control sample was at a level of 9.71 mM
Trolox/g d.m. for water extract, and 31.57 mM Trolox/g
d.m. for methanolic extract. In turn, for the sample with
added apples and cranberry it was 5.71 mM Trolox/g d.m.
for water extract, and 13.72 mM Trolox/g d.m. for
methanolic extract. Fruit addition, mainly mulberry, af-
fected the antiradical activity of muesli. Numerous pa-
pers demonstrating the beneficial antioxidative effect of
mulberry fruits are available in the literature. Chon et al.
[11] demonstrated that ethanolic extracts of mulberry
fruits scavenge radicals to the highest degree.
The total content of polyphenols is presented in Fig-
ure 3. The highest level of total polyphenols was noted
in the sample of muesli with added mulberry fruit, in
water extract, and then in methanolic extract: the level of
polyphenols was 5.65 and 3.29 mg of ferulic acid/g d.m.
of an extract, respectively. In turn, the muesli sample
with added apple and cranberry contained 1.71 mg of
ferulic acid /g d.m. for water extract, and 0.55 mg of fer-
ulic acid/g d.m. for methanolic extract.
An increase in polyphenol levels in muesli is ex-
plained by the increase in the amount of fruits which are
a source of these components. It was demonstrated in the
Figure 3. Polyphenolic content in muesli extract.
study by Ercisli and Orhan [10] that white mulberry
fruits contain as much as 181 mg in fresh mass. Similar
results comparing polyphenol content in various ana-
tomical parts of white mulberry were presented by Chon
et al. [11], who noted total polyphenol content in mul-
berry fruits at a level of 213 mg/kg. As may be con-
cluded from the study by Bae et al. (2007) mulberry fruit
extracts contained as much as 2570 µg/g of polyphenols
expressed as gallic acid. The relationship between poly-
phenolic compound content and antiradical activity was
also confirmed in this study. As demonstrated by Gundogdu
et al. [12] and Pawlowska et al. [23] rutin, chlorogenic,
gallic and caffeic acids are the predominant polyphenols
in white mulberry fruits.
3.3. Oxidative Stability Determination
Muesli is susceptible to lipid oxidation due to the high
content of unsaturated fatty acids. The oxidative proc-
esses also depend on the content of compounds which
may theoretically inhibit these unprofitable changes.
Oxidative stability was determined in the study by ex-
amination of the content of primary and secondary oxi-
dation products, and the results are presented in Table 3.
The content of primary oxidation products was in the
range of 5.78 meq O2/kg for the control sample to 9.47
meq O2/kg for the sample containing mulberry fruits.
The content of secondary oxidation products expressed
as an anisidine number was in turn nearly two-fold lower
in sample C (18.01) when compared to the reference
sample A (33.43). Various contents of primary and sec-
ondary oxidation products result probably from the dif-
ferent compositions of the examined muesli. Moreover,
as may be concluded from the study by Bae et al. [22],
active compounds of mulberry fruits considerably mod-
erate fat oxidation. It was demonstrated in model tests
that formation of secondary oxidation products was as
much as 23% higher.
3.4. Sensory Analysis
The results of sensory assessment are presented in
Figure 4. Beige color was predominant characteristic for
all samples. Purple and red colors were also noted in the
sample with apple and cranberry, while orange color was
additionally noticed in the sample with mulberry.
Table 3. Oxidative stability of muesli recorded by peroxide and
anizidine value.
Peroxide value [meq O2/kg] Anizidine value
Muesli A5.78 ± 0.76 33.43 ± 1.44
Muesli B5.92 ± 0.28 34.85 ± 1.95
Muesli C9.47 ± 0.47 18.01 ± 0.98
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J. Kobus-Cisowska et al. / Agricultural Sciences 4 (2013) 1 30-135
(a) colour of muesli
(b) taste of muesli
(c) odor of muesli, crunchiness, density and softening
Figure 4. Sensory analysis of muesli (a) colour of
muesli;(b)taste of muesli;(c)odor of muesli and
crunchiness, density, softening).
Cereal smell was predominant in all samples. Further,
a fruity smell was also perceived, which was especially
distinct in the sample with added apple and cranberry,
and mainly in the sample with added white mulberry.
Sweet and fruity taste was especially highly evaluated
in the examined samples. Also, a subtly cloying taste was
noticed, and even bitter to a small degree in the control
sample without fruits. Comparable crunchiness evalua-
tion results were obtained in the examination, however
the highest crunchiness was noted for muesli with white
mulberry – 4.66 points, then for the control sample –
4.09 points, and muesli with apple and cranberry –
3.81points (on a 1 - 10 scale, where 1 means soft muesli
flakes, and 10 – hard ones). People tend to like contrasts
in foods, and products which undergo changes in texture
during mastication are well liked [6]. As may be con-
cluded from these authors’ research, the choice of muesli
is mainly affected by a sweet taste, which may be de-
rived from dried fruits. It can be noticed in the results of
this study that sweet taste was to the highest degree de-
tectable in the sample of muesli C with added mulberry
Muesli including oat flakes, linseed, granulated bran,
cranberry, apple and white mulberry fruit was character-
ized by high nutritional value. The content of saturated
acids in muesli was at a level of about 13%, monoun-
saturated at a level of 37%, and polyunsaturated 50%.
Oleic acid was found in the highest amount, and linoleic
acid was predominant among polyunsaturated ones. The
study demonstrated less advanced oxidative changes of
the product with added white mulberry fruit. Moreover,
the examined samples exhibited antioxidative properties
measured in free radical tests with ABTS and DPPH,
which resulted from a higher content of polyphenolic
compounds also originating from dried fruits. The con-
ducted sensory analysis allowed us to notice that an ad-
dition of mulberry fruits profitably influenced the sen-
sory attractiveness of the product.
Thus, mulberry fruits may be an attractive component
of muesli due to an increase in antioxidative activity, as
well as profitable sensory properties and nutritional value.
Muesli based on oat flakes, granulated bran and linseed
with an addition of white mulberry fruits may constitute
an important element of a diet.
Financially supported by EU Project Nr POIG 01.01.02-00-061/0.
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