Wir gratulieren Dr. rer. nat. Julia Steiner herzlich zum erfolgreichen Abschluss ihrer Promotion!
In ihrer Arbeit „Extraction of water-insoluble 1,3-1,4-β-D-Glucan and Arabinoxylan from Brewer’s Spent Grain using Hydrothermal Treatment“ hat sie die nachhaltige Nutzung von Brauereinebenprodukten untersucht und damit einen wichtigen Forschungsbeitrag geleistet.

Als wertvolles Mitglied unseres Teams hat Julia über mehrere Jahre die Arbeit am Lehrstuhl für Brau- und Getränketechnologie unterstützt und bereichert. Wir freuen uns mit ihr über diesen Erfolg und wünschen ihr für die Zukunft alles Gute und viel Erfolg.

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In ihrer Dissertation untersucht Julia Steiner die Extraktion von ernährungsphysiologisch wertvollen Ballaststoffen aus Biertreber, einem Nebenprodukt der Bierherstellung, mit Hilfe der hydrothermalen Spaltung. Ziel ist es, Biertreber aufzuwerten und die gewonnenen Polysaccharide – insbesondere 1,3-1,4-β-D-Glucan und Arabinoxylan – für die Lebensmittelindustrie nutzbar zu machen.

Die Arbeit umfasst eine detaillierte Analyse der Zusammensetzung von Biertreber, eine Untersuchung verschiedener hydrothermaler Prozessbedingungen sowie die Entwicklung präziser Quantifizierungsmethoden für die extrahierten Ballaststoffe. Besonderes Augenmerk liegt auf der Erzielung definierter Molmassenbereiche, die für gesundheitsbezogene Wirkungen relevant sind, sowie auf der Minimierung unerwünschter Nebenprodukte wie HMF und Furfural.

Die Ergebnisse zeigen, dass durch gezielte Prozesssteuerung hohe Ausbeuten an löslichen β-Glucan- und Arabinoxylan-Fraktionen erzielt werden können, wobei eine Balance zwischen Gesamtausbeute und gewünschten Molmassenbereichen entscheidend ist. Die Arbeit liefert damit wertvolle Erkenntnisse für eine nachhaltige und ressourcenschonende Nutzung von Biertreber in der Lebensmittelindustrie.

Mehr Informationen finden Sie auf mediaTUM: https://mediatum.ub.tum.de/1769112?query=julia+steiner&show_id=1771233&srcnodeid=1769112

Wissenschaftliche Veröffentlichungen am BGT

Steiner, J.; Kupetz, M.; Becker, T.: Advancing Quantification of Water-Extractable Arabinoxylan in Beer: A High-Throughput Approach. Polymers
(2023) 15, 3959.

https://doi.org/10.3390/polym15193959

Water-extractable arabinoxylan (WEAX) may cause major problems during clarification processes in a brewery owing to its ability to form gel networks. However, high WEAX contents can also enhance the nutritional quality of the final product as they play an important role in the human diet. Therefore, precise quantification of WEAX is required. Current methods are very time- and resource-consuming as well as limited in the number of samples and in some cases provide low accuracy. Thus, a reproducible high-throughput method for the quantification of WEAX optimized for beer was developed, reaching recovery rates (RRs) of almost 100%. The assay is based on Douglas’s colorimetric method. Hydrolysis was conducted using glacial acetic acid to induce the formation of red color complexes resulting from the interaction between pentose degradation products and phloroglucinol. The method was successfully transferred to a multi-mode microplate reader to minimize the loss of color intensity over time and to obtain a high throughput. By using 96-well plates, up to 40% of the previous analysis time could be saved, and a larger number of samples could be analyzed in one batch. The collected data determined xylose as an optimal calibration standard due to high accuracy and reproducibility. The respective AX control standards showed RR within the range of 95–105% without exception. To validate and show the ruggedness of the modified method, WEAX concentration in seven commercial German beers (e.g., lager, pilsner, wheat beer, non-alcoholic beer) was quantified. Interfering hexose sugars that lead to measurement errors when analyzing samples with high amounts of fermentable sugars (e.g., non-alcoholic beer produced by limited fermentation) were eliminated by Saccharomyces diastaticus fermentation. Further investigations were carried out by means of LC-MS in order to obtain additional information about the reddish product in the hydrolyzed samples. In this context, C16H12O6 could be identified as one of numerous condensation products, contributing to the coloring. The collected data showed the impact of diverse factors on the measured AX concentration and helped optimize the experimental procedure for a high sample throughput with precise and highly reproducible results. The proposed quantification method should be primarily used in completely fermented finished beer to emphasize the time aspect. Wort samples and non-alcoholic beer produced by limited fermentation can be also analyzed, but only after fermentation with S. diastaticus.

Lehnhardt, F., Steiner, J., Gastl, M., Becker, T.: Prediction Power and Accuracy of Forced Ageing – Matching Sensory and Analytical Results for Lager Beer. BrewingScience (73), 2018, 39-48

doi:10.23763/BrSc18-05lenhardt

The most common way to predict the shelf life and sensory stability of lager beer is via forced ageing at elevated temperature (40 °C). However, practical results often indicate that forced ageing alters the flavour profile unlike natural ageing. To assess the prediction power of forced ageing using both sensorial and analytical approaches, a lager and a pilsner beer were stored for up to 17 months at 20 °C (natural ageing) and at 40 °C for up to 9 days (forced ageing). The beers were tested by sensory analyses (DLG 5-Point Scheme [Deutsche Landwirtschafts-Gesellschaft e. V], acceptancy, and ageing descriptors). In addition, volatile compounds were measured by solid-phase microextraction (SPME) after on-fibre derivatization with o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA). Based on (i) sensory analyses (DLG rating and acceptancy test) and (ii) the sum of analytical ageing indicators, it was shown that forced ageing over 4 days at 40 °C was able to well predict natural ageing of 3–5 months. Quantitative descriptive analysis (QDA) revealed a difference in the aroma profile of the two ageing processes. Furthermore, it was found that gas chromatography-olfactometry (GC-O) was able to determine whether samples were aged; although it was not suitable for the prediction of the degree of ageing. Between natural and forced ageing, no clear correlation between the detected aroma active indicators was found. Principal components analysis (PCA) of chosen ageing compounds (i.e., their tendency to increase linearly with ageing) revealed that 4 days of forced ageing was not able to satisfactorily predict all ageing indicators. Nevertheless, some indicators increased linearly in both ageing processes and so could be used for prediction. Therefore, breweries should be aware of the sensory and analytical discrepancies between forced and natural ageing and should critically reconcile the different prediction methods.

Steiner, J., Kupetz, M., Becker, T.: Influence of Hydrothermal Treatment of Brewer’s Spent Grain on the Concentration and Molecular Weight Distribution of 1,3-1,4-β-D-Glucan and Arabinoxylan. Foods, 2023

doi:10.3390/foods12203778 

Brewer’s spent grain (BSG) is the most abundant residual in the brewing process. Non-starch polysaccharides such as 1,3-1,4-β-D-glucan (β-glucan) and arabinoxylan (AX) with proven beneficial effects on human health remain in this by-product in high amounts. Incorporating the valuable dietary fiber into the food industry could contribute to a healthy diet. However, a major challenge is extracting these dietary fibers (i.e., β-glucan and AX) from the solid residue. In this study, hydrothermal treatment (HT) was applied to dissolve the remaining water-insoluble carbohydrates from BSG with the aim to extract high amounts of β-glucan and AX. Particular focus was placed on the molecular weight (MW) range above 50 kDa and 20 kDa, respectively, as these are considered to have health-promoting effects. Different treatment temperatures, reaction times, and internal reactor pressures were tested to determine the best process settings to achieve high yields of β-glucan and AX and to examine the influence on their molecular weight distribution (MWD). Overall, 85.1% β-glucan and 77.3% AX were extracted corresponding to 6.3 g per kg BSG at 160 °C and 178.3 g kg−1 at 170 °C, respectively. However, less than 20% of both fiber substances were in the desirable MW range above 50 kDa and 20 kDa, respectively. When lower temperatures of 140 and 150 °C were applied, yields of only 3.0 g kg−1 β-glucan and 128.8 g kg−1 AX were obtained, whereby the proportion of desirable fiber fractions increased up to 45%. Further investigations focused on the heat-induced degradation of monosaccharides and the formation of undesirable by-products (i.e., HMF and furfural) that might pose a health risk.

Steiner, J., Franke, K., Kießling, M., Fischer, S., Töpfl, S., Heinz, V., & Becker, T.: Influence of hydrothermal treatment on the structural modification of spent grain specific carbohydrates and the formation of degradation products using model compounds. Carbohydrate Polymers , 2017

doi:10.1016/j.carbpol.2017.12.038

Brewer’s spent grain (BSG) constitutes various valuable carbohydrates that may contribute to a healthy diet. These components may be obtained from BSG via hydrothermal treatment (HT), a procedure for dissolving water-inextricable carbohydrates. The objective of this study was to investigate HT as an environmentally friendly technology for extracting high-molecular-weight fiber with proven beneficial effects on human health. Cellulose, β-glucan, and arabinoxylan (AX) served as model substances and were subjected to auto-hydrolysis at different temperatures and reaction times. The results were evaluated in terms of structural and chemical characteristics. When the treatment temperature was increased, the original weight-average molar mass of AX (370 kDa) and β-glucan (248 kDa) decreased gradually (<10 kDa), and the molar mass distribution narrowed. Further investigations focused on the heat-induced formation and elimination of monosaccharides and undesirable by-products. The concentrations of by-products were successfully described by kinetic models that can be used to optimize the hydrolysis process.

Steiner, J.; Procopio, S.; Becker, T.: Brewer’s spent grain: source of value-added polysaccharides for the food industry in reference to the health claims. European Food Research and Technology 241 (3), 2015, 303-315

doi:10.1007/s00217-015-2461-7

Brewer’s spent grain (BSG) is the most abundant by-product of the brewing industry, constituting approximately 85 % (w/w) of the total by-products generated during beer production. Rich in cellulose and non-cellulosic polysaccharides, lignin, and proteins, BSG provides extra nutritional value, thereby arousing the interest of the food industry. Annually, around 3.4 million t of BSG are produced within the European Union, and Germany contributes approximately 2 million t. BSG is reused either substantial or energetic. However, its main application has been limited to animal feeding. Based on the intense global pressure toward green environmental technology and increasing regulations in the feed sector, alternative application fields have gained importance. Because of its high protein and fiber contents, BSG can be an attractive source for value-added products in human nutrition. The focus is on the reported health effects of (1–3,1–4)-β-d-glucan and arabinoxylan (AX). Several scientific studies have shown that barley (1–3,1–4)-β-d-glucan reduces blood cholesterol levels. A cause and effect relationship has been established between the consumption of AX from wheat endosperm and the reduction of postprandial glycemic responses. The intention of this review is to focus on the extraction of (1–3,1–4)-β-d-glucan and AX from BSG as a source of value-added compounds for use as a nutraceutical. In view of AX and (1–3,1–4)-β-d-glucan yield, different methods of extraction are presented. Finally, technological trends and future perspectives to expand this market are discussed, focusing on promising strategies such as the use of pressurized hot water extraction.

20. Oktober 2025

Fabian Lauck

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