BME VBK, Department of Applied Biotechnology and Food Science
the quality of gluten-free products
Introducing the research area
are non-starch polysaccharides classified to the hemicelluloses (more
specifically to pentosans),
which are primarily cell wall constituents of cereal grains (mainly rye and
wheat) . They have a significant nutritional importance as a dietary fiber
and a bioactive
. Their unique property is that they are able to cross-link in oxidative
media, so they can be used to create cross-linked structures . During my
work I studied the possibility of this in gluten-free model systems for
partial substitution of the missing gluten network.
Brief introduction of the research
research work was carried out in the BUTE ABÉT
Research Group of Cereal Science and Food Quality supervised by Dr. Sándor
The main research activities of the group include the examination of the
composition and functional properties of plant (cereal) components (mainly
proteins, carbohydrates and fibers), allergen analysis and reference material
development, and the development of measuring instruments and functional food
History and context of the
has been part of human nutrition for thousands of years. Its versatile use is
associated with the gluten proteins
in the kernel. Under the influence of hydration and mechanical work
(kneading), the gluten proteins create a complex cross-linked structure, the
so called gluten network, which results in a flexible and extensible dough
with gas retention capability. The consumption of wheat and other cereals with
similar protein compositions, such as rye, barley or triticale is not possible
for nearly 1% of the population due to various disorders (e.g. celiac disease
In their case, currently, strict lifelong gluten-free diet is the only
treatment . Since the role of wheat in our diet is of paramount importance,
it is not easy for some consumers to switch to a gluten-free diet. During the
hydration of gluten-free flours (e.g. rice, corn), the material system
characteristic of the structure of the wheat dough is not developed.
Therefore, the technological behavior of the dough (viscosity, gas retention,
etc.) and the improvement of end product properties are generally achieved by
the use of composite flours or hydrocolloids.
Although gluten-free bakery products are now available in a big variety, most
of them still lag behind the nutritional value, technological and organoleptic
qualities of wheat products; therefore the demand for better quality products
remains significant .
The research goals, open questions
possible solution for improving nutritional value and partial replacement of
gluten may be the enrichment of gluten-free raw materials with dietary fibers,
so called arabinoxylans (AX), which can be cross-linked by the formation of an
oxidative medium based on enzyme reactions.
(POx) can be a promising alternative to chemical oxidizing agents and to the
more widely used glucose oxidase of similar function, thanks to its improved
efficiency and broader substrate specificity. POx catalyzes the oxidation of a
number of mono- and
derivatives and H2O2.
By the formation of H2O2, the feruloyl groups of AXs may
oxidize and thus cross-link between the individual molecules (Figure 1).
Figure 1: Supposed mechanism of AX crosslinking
The aim of my work was to investigate the effect of fiber addition and enzyme
treatment on the rheological properties of gluten-free dough/suspension and on
the structure of macromolecules and micromorphological properties. In
addition, my goal was to examine the effects of treatments on the quality of
the final product in simple yeast leavened as well as sourdough leavened test
my work, I sought to find out whether crosslinking of AX molecules has taken
place and to what extent affect the properties of gluten-free model matrices
and end products.
Materials and their characterization
During the experiments, buckwheat
flours were used as model matrices; the addition experiment was performed
using experimental arabinoxylan (AX) isolate and pyranose oxidase produced at
The chemical composition of the flours (moisture, ash, protein, fat, dietary
fiber) was determined by standard methods. The contents of flour and isolate
AX were measured by gas
Examination of rheological properties
is a discipline for describing the flow and deformation properties of
materials. The rheological behavior is determined by the interactions between
the molecules that make up the system. A number of measuring instruments,
mainly based on empirical principles, have been developed to study these in
the field of food and cereal analysis .
measurement techniques were used to test the mixing and viscous properties of
millet and buckwheat-based dough systems. These instruments measure the
resistance to the kneading arm or mixing blade as a function of time. By
plotting the measurement points the profile characteristic of the given sample
is shown and the characteristic parameters of the curves can be determined.
Baking tests provide direct information on the organoleptic and technological
properties of the final product. These measurements typically require high
amount of sample, but in our case AX isolate and enzyme were only available in
limited amounts. Therefore, I adapted the micro-scale baking method for
gluten-free flours that I had developed for wheat flour. Because gluten-free
loaves are more compact and flattened in the absence of gluten network, I
increased the amount of flour required from 10 g to 15 g to form a crumb with
an evaluable surface area. Measurements were made using a simple yeast method
and the addition of gluten-free dried sourdough. According to the literature,
the lower pH provided by the sourdough favors the formation of cross-links
between AX molecules in rye breads. In addition, sourdough
might have many other positive effects (increased solubility of proteins,
formation of flavors and flavorings, softer crumb, etc.). To characterize the
test loaves, I determined the baking loss (expressed as a percentage of water
lost during baking) and the volume. In addition, I studied the crumb hardness
using a texture analyzer. I also took pictures of the loaves and their
cross-sections, which were evaluated using digital image
Characterization of raw materials
expected, white flours were a chemically simpler material system, mainly
containing the starchy endosperm. As a result, they can be characterized by
significantly lower fiber and / or AX content, i.e. less reactive groups than
wholemeal flours (Figure 2).
Figure 2: Chemical composition of millet and buckwheat flours
Examination of the rheological properties of model doughs
most cases, AX addition caused a significant reduction in the consistency of
the doughs. During the enzymatic treatment of dough systems containing added
AX, higher consistency was measured than with untreated AX dosed dough. All
these suggested cross-linking between AX molecules. However, I observed that
the formation of oxidative media without AX addition also caused changes in
the properties of the dough (Figure 3).
Figure 3: Consistency of white buckwheat flour based doughs measured by micro-doughLAB
The H2O2 produced by the enzyme does not specifically affect the individual
flour constituents; for example, it may induce the formation of intermolecular
bonds between proteins, but occurrence of AX-protein interactions between the
feruloyl groups of AXs and protein tyrosyl groups cannot be excluded, either.
Significant changes were also observed in the viscous properties as a result
of AX dosing and enzyme treatment, which were in harmony with previous results
(Figure 4). In most cases, the use of POx in systems both with AX and without
AX had an effect on viscous behavior. For the latter, the oxidation of starch
was assumed .
Figure 4: Viscosity of white millet flour based suspensions measured by RVA at
Investigation of molecular and micromorphological properties
Further experiments were carried out to support the results of rheological
studies. On the basis of these results, it could be concluded that there had
been an increase in the size of the AX molecules, which was also supported by
the reduction of free ferulic acid content by enzyme treatment (Figure 5).
Figure 5: Size distribution of AX molecules and free ferulic acid contents
measured in white millet doughs
The amount of soluble protein fractions also decreased significantly as a
result of enzyme treatment, which indicated the formation of aggregates or
macromolecular complexes (Figure 6).
Figure 6: Chromatograms of soluble and insoluble protein fractions of white
The size distribution of starch molecules also showed an increase in size,
which confirmed the oxidation of starch molecules (Figure 7).
Figure 7: Chromatograms of starch of white millet doughs
The micromorphological structure of the dough has also been modified, during
which the enzyme treatment causes AX to appear as a binder in the space
between the starch particles.
Figure 8: SEM images of the micromorphological structure of white millet dough
summary, the modification of proteins and starch molecules, as well as their
interaction with AX molecules, may have played a role in changes in
Results of end product tests
addition reduced the baking loss due to the water-binding ability of soluble
AX molecules. At the same time, the crumb of the loaves became softer. In the
sourdough systems, the specific volume was reduced by AX, while in the case of
yeast leavened loaves it did not change it at all, or merely slightly. On the
basis of the results it was proven that the effect of AX and enzyme treatment
has a visible impact on the quality of the final products (Figure 9).
Figure 9: Crumb structure, baking loss, specific volume and hardness of yeast
leavened and sourdough millet breads
Expected impact and further
This research work has been carried out with our partner institution
(University of Natural Resources and Life Sciences in Vienna) in the frame of
OTKA (ANN 114554) joint project, and we plan to continue this work in the next
application cycle. The results have been published in one of the most
prestigious journals in the field, the Food Hydrocolloids (IF: 5,832, Q1). In
the continuation of the research, I would also like to study the molecular
processes in the final products, as well as to carry out experiments with
additional gluten-free materials. I plan to publish the further results in a
similarly prestigious journal.
List of corresponding own publications
[S1] Németh, R., Bender, D., Jaksics, E., Calicchio, M., Langó, B.,
D’Amico, S., Török, K., Schoenlechner, R., Tömösközi, S., 2019. Investigation
of the effect of pentosan addition and enzyme treatment on the rheological
properties of millet flour based model dough systems. Food Hydrocolloids. 94,
381–390. IF: 5,832
[S2] Bender, D., Németh, R., Cavazzi, G., Turoczi, F., Schall, E.,
D’Amico, S., Török, K., Lucisano, M., Tömösközi, S., Schoenlechner, R., 2018.
Characterization of rheological properties of rye arabinoxylans in buckwheat
model systems. Food Hydrocolloids. 80, 33–41. IF: 5,832
[S3] Langó, B., Fehér, A. G., Bicskei, B. Z., Jaksics, E., Németh, R.,
Bender, D., D’Amico, S. Schoenlechner, R., Tömösközi, S. (2018). The Effect of
Different Laboratory-scale Sample Preparation Methods on the Composition of
Sorghum (Sorghum bicolor L .) and Millet ( Panicum miliaceum L .) Milling
Fractions. Periodica Polytechnica Chemical Engineering, 62(4), 426–431.
https://doi.org/10.3311/PPch.12846, IF: 0.877
[S4] Tömösközi, Sándor, Németh, Renáta, Roznár, Petra, Denisse, Bender,
Jaksics, Edina, Turóczi, Fanni, Török, Kitti, Regine, Schönlechner (2018).
sikérfehérjéket nem tartalmazó (gluténmentes) termékek táplálkozási és
technológiai minőségének fejlesztése. Magyar Kémiai Folyóirat – Kémiai
(1997-) 124: 3 pp. 101-107, 7 p. http://doi.org/10.24100%2FMKF.2018.03.101,
[S5] Bender, D., Németh, R., Wimmer, M., Götschhofer, S., Biolchi, M.,
Török, K., Tömösközi, S., D’Amico, S., Schoenlechner, R. (2017). Optimization
of Arabinoxylan Isolation from Rye Bran by Adapting Extraction Solvent and Use
of Enzymes. Journal of Food Science, 00(0), 1–7. IF: 1,815
[S6] Bender, D., Schmatz, M., Novalin, S., Németh, R., Chrysanthopoulou,
F., Tömösközi, S., Török, K., Schoenlechner, R., Amico, S. D. (2017). Chemical
and rheological characterization of arabinoxylan isolates from rye bran.
Chemical and Biological Technologies in Agriculture, 4(14), 1–8., IF:0
 Buksa, K., Praznik, W., Loeppert, R., & Nowotna, A. (2016).
Characterization of water and alkali extractable arabinoxylan from wheat and
rye under standardized conditions. Journal of Food Science and Technology,
 Mendis, M., & Simsek, S. (2014). Arabinoxylans and human health. Food
Hydrocolloids, 42(P2), 239–243.
 Decamps, K., Gryp, G., Joye, I. J., Courtin, C. M., & Delcour, J. A.
(2014). Impact of pyranose oxidase from Trametes multicolor, glucose oxidase
from Aspergillus niger and hydrogen peroxide on protein agglomeration in wheat
flour gluten-starch separation. Food Chemistry, 148, 235–239.
 Lebwohl, B., Ludvigsson, J. F., & Green, P. H. R. (2015). Celiac disease
and non-celiac gluten sensitivity. BMJ, 351, h4347.
 Pellegrini, N., & Agostoni, C. (2015). Nutritional aspects of gluten-free
products. Journal of the Science of Food and Agriculture, 95(12), 2380–2385.
 Dap, T., Poji, M., Hadna, M., & Torbica, A. (2011). The Role of Empirical
Rheology in Flour Quality Control. In I. Akyar (Ed.), Wide Spectra of Quality
Control (pp. 335–360).
 Pereira, J. M., Evangelho, J. A., Moura, F. A., Gutkoski, L. C., Zavareze,
E. R., & Dias, A. R. G. (2017). Crystallinity, thermal and gel properties of
oat starch oxidized using hydrogen peroxide. International Food Research
Journal, 24(4), 1545–1552.