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BMe Research Grant |
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George A. Olah Doctoral School of Chemistry and Chemical Technology
Department of Applied Biotechnology and Food Science
Supervisor: Dr. Tömösközi Sándor
Wheat Aleurone-rich Food and Arabinoxylan Oxidation
Introducing the research area
My research focuses on the examination of a newly developed, industrially produced flour that is enriched in the aleurone layer. The applicability of the aleurone-rich flour in pasta and bread production and its effect on the nutritional values of food products were examined. Besides, the oxidative modification of its most abundant non-starch polysaccharide component, arabinoxylan (AX) was also investigated.
Brief introduction of the research place
I carried out my research at BME ABÉT Department, GEMKUT research group under the supervision of dr.Sándor Tömösközi and at ETH Zürich, Laboratory of Food Biochemistry research group under the supervision of Prof. Laura Nyström. The mainstream research activity of the Hungarian group is related to food quality, qualification and safety and to cereal science and technology. The Swiss research group focuses on the detailed composition of food, especially the food components that have beneficial effects on human health.
History and context of the research
Increased intake of dietary fibre is preventive against widespread, diet-related diseases (e.g. diabetes diet type II or CVD). With cereal fibre enrichment, it is possible to increase the nutritional values of food, however, at the same time, dietary fibre incorporation provokes a pronounced decrease in consumer acceptance hindering the increase of dietary fibre intake in the population [1].
This can be observed in the case of wheat processing, which is one of the major dietary fibre sources. Although modern milling technologies are able to produce milling products that contains different anatomical parts of the wheat kernel in different proportions, the main product of milling industry is refined flour. The fibre-rich cereal bran is considered to be a by-product and is mainly used as livestock feed or energy source. Inner layers of the bran, mainly the aleurone layer have better functionality than the whole bran. Besides, the aleurone layer contains high amounts of bioactive components and is considered to be the major contributor to beneficial health effects associated with whole grain consumption. The utilization of this nutritionally valuable fraction as food would be highly beneficial from economical point of view and could lead to better utilisation of the dietary potential of the whole grain. For this purpose, it is necessary to develop new, fibre-rich food base materials that contain the beneficial fractions of the wheat bran, and in this way, the incorporation of fibre components into the food matrix has lower impact on the decrease of consumer acceptability [2].
Besides, there is also a need for the evaluation of dietary fibre molecules individually since they all have different health-related effects and technological properties. The improvement of the techno-functionality of a given fibre component with enzymatic/chemical modification might provide valuable knowledge about the fibre component itself and can contribute to the improvement of fibre-rich fractions at the molecular level. One of these modification strategies can be the oxidation of fibre components. It can be performed by oxidative enzymes (e.g. peroxidase) or with reactive hydroxyl radicals (•OH). The cross-linking of arabinoxylan (AX), which is the most abundant cereal fibre component, by enzymatic oxidation (AX) has already been studied [3]. In contrast, the •OH oxidation of AX has not been investigated as yet. In the case of beta-glucan it was demonstrated that the •OH oxidation improved its health-related properties, namely its bile acid-binding capacity, denoting an increased blood cholesterol-reducing effect [4]. The cholesterol cannot be oxidized into carbon-dioxide and water in the human body, but can be excreted via the feces in the form of bile acids. The more bile acids the dietary fibres bind, the more they reduce the cholesterol level [5].
The research goal, open questions
The general aim of my research was to make a contribution to the development of marketable cereal fibre-rich food products and to the understanding of the structure-function relationships of cereal fibre components. For the latter purpose, the oxidative modification of AX was investigated.
The focus areas of my research:
1. the examination of the effects of aleurone-rich flour addition on pasta and bread quality (product-specific investigation, textural and sensory properties and consumer acceptance)
2. the effect of •OH oxidation on the structural properties of wheat AX
3. the effect of •OH oxidation and oxidative cross-linking on the bile-acid binding and on the technological properties of AX-flour mixtures (dough development and pasting properties)
Methods
Characterization of food model products
Pasta and bread products were made with laboratory procedures, using aleurone-rich flour and conventional wheat flour. In order to reveal the effects of the addition the new milling fraction, wheat flour-aleurone-rich flour mixtures were prepared and examined. The model products were examined with complex qualification methods: compositional measurements, product-specific examinations, instrumental texture analysis (with Texture Analyser instrument), sensory profiling (Quantitative Descriptive Analysis) and Penalty Analysis were also carried out.
Oxidation of arabinoxylan (AX)
AX was extracted from aleurone-rich flour. •OHs were generated with ascorbate driven Fenton reaction, which is the reaction of hydrogen peroxide, ascorbate and ferrous iron. AX cross-linking were induced with peroxidase/H2O2; a method well known in literature. The formation and the effect of •OHs on AX were investigated by means of electron paramagnetic resonance and viscosity measurements in aqueous AX solution. •OH-treated and enzymatically cross-linked AX samples were prepared and examined for structural (molecular size, ferulic acid content, A/X ratio), health-related (bile acid-binding capacity) and techno-functional properties AX-wheat flour mixtures.
Bile acid-binding of AX was examined with kinetic analysis of bile salt passage across a dialysis membrane (Fig. 5) [5]. The techno-functional properties were examined in wheat flour/AX blends: dough development (micro-doughLAB) and pasting properties (Rapid Visco Analyser) were investigated.
Results
Characterization of products made of aleurone-rich flour
It was shown that the aleurone-rich flour is suitable for bread and pasta production, without applying any flour improver additives. Aleurone-rich flour addition improved the nutritional balance of bread and pasta compared to conventionally consumed products through increasing the dietary fibre and protein content at the expense of readily digestible carbohydrates. Our results show that the aleurone-rich flour addition results in considerably more beneficial composition than whole-meal products (Fig. 1) [S1].
Fig. 1: Comparison of the composition of pasta made of aleurone-rich flour with conventional pasta and whole-meal pasta
The cooking and textural characterisation of pasta showed that the aleurone-rich flour addition did not provoke poor quality characteristics (lower firmness, higher adhesiveness and cooking loss) (Fig. 2) being generally observed for fibre addition. According to my assumptions, this behaviour was caused by the particular properties of aleurone-rich flour: high protein content, high fat content and fine particle size of the aleurone-rich flour might have contributed to processes that compensated the negative effects of fibre incorporation. Based on these results we suppose that the aleurone-rich flour is more applicable in value-added pasta production than wheat bran fractions or whole-grain flour. [S1; S7]
Fig. 2: Cooking loss, stickiness and firmness of pasta made from conventional pasta flour and aleurone-rich flour as the function of aleurone-rich flour content
Examining bread samples (Fig. 3), the aleurone-rich flour addition has led to a lower quality that is general in the case of fibre addition. Presumably, dietary-fibre incorporation and related substances (e.g. flavour-active phenolic compounds) were responsible for these changes in the first place. Penalty analysis showed that the too intense odour, flavour as well as bitter taste and the too weak sweet taste were associated with decreased acceptability of bread made of the aleurone-rich flour (Fig. 3). Based on the results I suggested possible ways of product development: the lack of sweet taste can be compensated with natural non-sugar sweeteners, or the bread quality could potentially be improved with fibre modification processes e.g. endoxylanase enzymes. [S2]
Fig. 3: Bread made of the mixture of aleurone-rich flour (AB) and wheat flour (WB) (left) and the properties of bread made of aleurone-rich flour that are responsible for the decrease of consumer acceptance (Penalty analysis, right). The significant properties are marked with the red circle
Oxidation of arabinoxylan
The effect of •OH oxidation on AX was investigated for the first time. It was demonstrated that •OH oxidation did not induce ferulic acid dimerization, which was reported by all of the publications working with AX oxidation [3]. Hence this type of oxidation does not induce gelation processes in aqueous AX solution, which is also a generally reported phenomenon. although the examined AX sample was capable of gel formation upon enzymatic oxidation. Instead of gelation, •OH oxidation provoked viscosity decrease in AX solution (Fig. 4), which resulted from the oxidative degradation of the polymer. The degradation could be enhanced with a higher concentration of oxidizing agents and at elevated temperatures. [S3]
Fig. 4: The effect of hydroxyl radical oxidation on the arabinoxylan solution. Along with the increase of hydroxyl radical formation (relative EPR signal), the viscosity decreases (left) and the solution loses its pseudoplastic characteristic (right)
•OH oxidation did not affect the bile acid retention of AX, while cross-linking significantly enhanced this property, presumably due to the bile salt retention-effect of the gel structure, which slows down the diffusion of bile salts (Fig. 5). This result suggests that cross-linking enhances the cholesterol-lowering effect of AX. [S4]
Fig. 5: The method of bile acid-binding capacity determination (left) and the effect of oxidation of arabinoxylan on its bile acid-binding capacity (right). The hydroxyl radical oxidation (•OH1 and •OH2 blue) does not induce any changes, while the cross-linking (POD, black) slows down the passage of bile acids through the membrane (the permeability constant decreases, right inner diagram), which suggests increased bile acid binding capacity
The effect of AX oxidation on pasting properties and on dough development of flour was presented for the first time. Cross-linked AX caused higher water absorption than the non-oxidized AX, most likely due to its gel structure, which has higher water holding capacity. In spite of this, •OH-oxidized AX caused significantly lower water absorption when added to wheat flour, probably due to its lower molecular weight.
Fig. 6: The effect of enzymatic cross-linking and hydroxyl radical oxidation of AX on the pasting properties of a flour-water slurry. The method reveals the technological behaviour of the flour
•OH-oxidized samples decreased, cross-linked AX increased the viscosity parameters during RVA measurements compared to the addition of non-oxidized AX (Fig. 6). These differences also seem to originate from the decreasing molecular weight and the gel structure. [S4]
Fig. 7: The effects of oxidative modification of arabinoxylan (hydroxyl radical (•OH) and enzymatic oxidation) on its structure, bile acid-binding capacity and on its functionality in flour systems
Expected impact and further research
Industrial realization:
Related to my research, the company Gyermelyi Zrt. introduced the pasta products made of aleuron-rich flour to the market in 2014, under the brand name DiVita. Based on my results, development of bakery products made of aleurone-rich flour can continue.
Research:
My results support the interpretation of the AX’s role in the complex flour system, as well as they might open up new prospects for the utilization of AX in food matrices. These might be the subject of future studies. The in vivo investigation of the bile acid-binding capacity of cross-linked AX is highly expedient since it might increase the health-supportive effect of AX.
Scientific presentations:
I presented my research at several Hungarian and international conferences as oral or poster presentations. My work was awarded with “Silver Award” in the 12th European Young Cereal Scientists and Technologists Workshop.
Publications, links, references
Publications (IF: impact factor):
[S1.] Bagdi, A., Szabó, F., Gere, A., Kókai, Z., Sipos, L., & Tömösközi, S. (2014). Effect of aleurone-rich flour on composition, cooking, textural, and sensory properties of pasta. LWT – Food Science and Technology, 65, pp. 762–769 IF: 2.47
[S2.] Bagdi, A., Tóth, B., Lőrincz, R., Szendi, S., Gere, A., Kókai, Z., & Tömösközi, S. (2016). Effect of aleurone-rich flour on composition, baking, textural, and sensory properties of bread. LWT – Food Science and Technology, 65, pp. 762–769 IF: 2.47
[S3.] Bagdi, A., Tömösközi, S., Nyström L. (2016) Hydroxyl radical oxidation of feruloylated arabinoxylan. Carbohydrate Polymers, Accepted, Under publication - IF: 4.22
[S4.]Bagdi, A., Tömösközi, S., Nyström L. (2016) Structural and functional characterization of oxidized feruloylated arabinoxylan from wheat. Food Hydrocolloids, 63, 219-225. - IF: 3.86
[S5.] Új típusú, funkcionális komponensekben gazdag búzaőrlemény összetételi és reológiai jellemzése. Lőrincz Réka, Bagdi Attila, Szendi Szilvia, Bucsella Blanka, Tömösközi Sándor; Élelmiszer Tudomány Technológia, LXVI. 2012. No. 3., pp. 5–12 IF: –
[S6.] Egy különleges malomipari termék az egészségtámogatás szolgálatában. Bucsella Blanka, Bagdi Attila, Szendi Szilvia, Tömösközi Sándor; Magyar Gasztroenterológia July 2012, special issue 8–13 IF: –
[S7.] Új fejlesztésű, piaci bevezetés előtt álló egészségtámogató komponensekben gazdag búzaőrlemény összetételi jellemzése. Szendi Szilvia, Bucsella Blanka, Bagdi Attila, Tóth Béla, Tömösközi Sándor – Élelmiszer - Tudomány Technológia LXVIII.:(3) pp. 15–23 (2014) IF: -
Links:
EUFIC: The role of dietary fibres.
Measurement of free radicals: electron paramagnetic resonance on the wikipedia.
References:
[1] Rakha, A. (2013). (First edit., pp. 211–230). Cambridge: Woodhead Publishing Limited.