Wir gratulieren Dr. Stefan Ritter ganz herzlich zur erfolgreichen Promotion!
In seiner Dissertation „Germination as a Modulation Tool to Improve Legumes as Substrate for an Optimized Lactic Acid Fermentation“ hat Stefan untersucht, wie sich durch gezielte Keimung die Eigenschaften von Hülsenfrüchten verbessern lassen – um Aroma und Verträglichkeit zu optimieren und Flatulenzen zu reduzieren.

Mit dieser Arbeit hat er einen wertvollen Beitrag zur Weiterentwicklung pflanzlicher Fermentationsprozesse geleistet und damit das Forschungsteam am Lehrstuhl für Brau- und Getränketechnologie bereichert.

Wir freuen uns mit ihm über diesen Erfolg und wünschen ihm für die Zukunft alles Gute, viel Freude und Erfolg bei seinen kommenden Projekten.

Inhalt

In seiner Dissertation hat Stefan Ritter untersucht, wie sich durch gezielte Keimung die Eigenschaften von Lupinen und Ackerbohnen so verändern lassen, dass sie sich besser für proteinreiche Erfrischungsgetränke eignen. Ziel war es, die Flatulenz-fördernden Oligosaccharide abzubauen, die Proteinlöslichkeit zu erhöhen und das Aroma zu verbessern.

Er entwickelte dafür eine Vorbehandlungsstrategie, bei der die Substrate vor der Milchsäurefermentation moduliert wurden. So konnten alle getesteten Milchsäurebakterienstämme gut wachsen, was die Auswahl geeigneter Stämme erleichterte. Anschließend wurden die Fermentationsparameter optimiert, wobei Temperatur und Fermentationsdauer entscheidenden Einfluss auf das Aroma- und Geschmacksprofil hatten.

Die Arbeit zeigt, dass sich durch die Kombination von Keimung und gezielter Milchsäurefermentation die sensorischen Eigenschaften von Hülsenfrüchten deutlich verbessern lassen, während gleichzeitig die Proteinlöslichkeit steigt und Flatulenz-fördernde Bestandteile reduziert werden.

Wissenschaftliche Veröffentlichungen am BGT

Ritter, S. W., Thiel, Q. P., Gastl, M. I., Becker, T. M.: Optimizing the fermentation parameters in the Lactic Acid Fermentation of Legume-based Beverages–a statistically based fermentation. Microbial Cell Factories (23), 2024

doi:https://doi.org/10.1186/s12934-024-02522-x

Background

The market for beverages is highly changing within the last years. Increasing consumer awareness towards healthier drinks led to the revival of traditional and the creation of innovative beverages. Various protein-rich legumes were used for milk analogues, which might be also valuable raw materials for refreshing, protein-rich beverages. However, no such applications have been marketed so far, which might be due to unpleasant organoleptic impressions like the legume-typical “beany” aroma. Lactic acid fermentation has already been proven to be a remedy to overcome this hindrance in consumer acceptance.

Results

In this study, a statistically based approach was used to elucidate the impact of the fermentation parameters temperature, inoculum cell concentration, and methionine addition on the fermentation of lupine- and faba bean-based substrates. A total of 39 models were found and verified. The majority of these models indicate a strong impact of the temperature on the reduction of aldehydes connected to the “beany” impression (e.g., hexanal) and on the production of pleasantly perceived aroma compounds (e.g., β-damascenone). Positively, the addition of methionine had only minor impacts on the negatively associated sulfuric compounds methional, dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide. Moreover, in further fermentations, the time was added as an additional parameter. It was shown that the strains grew well, strongly acidified the both substrates (pH ≤ 4.0) within 6.5 h, and reached cell counts of > 9 log10 CFU/mL after 24 h. Notably, most of the aldehydes (like hexanal) were reduced within the first 6–7 h, whereas pleasant compounds like β-damascenone reached high concentrations especially in the later fermentation (approx. 24–48 h).

Conclusions

Out of the fermentation parameters temperature, inoculum cell concentration, and methionine addition, the temperature had the highest influence on the observed aroma and taste active compounds. As the addition of methionine to compensate for the legume-typical deficit did not lead to an adverse effect, fortifying legume-based substrates with methionine should be considered to improve the bioavailability of the legume protein. Aldehydes, which are associated with the “beany” aroma impression, can be removed efficiently in fermentation. However, terminating the process prematurely would lead to an incomplete production of pleasant aroma compounds.

Ritter, S., Luber, C., Gastl, M., Becker, T.: Identification of promising lactic acid bacteria for the fermentation of lupine- and faba bean-based substrates to produce refreshing protein-rich beverages—A strain screening. Food Frontiers, 2024, 1-28

doi:https://doi.org/10.1002/fft2.452

Lupines and faba beans are rising stars among legumes as sources of valuable, vegan plant-based proteins. To enter new application areas like the production of protein-rich refreshing beverages, the typical beany aroma impression has to be overcome, and the sensory appearance has to be improved, as it can be accomplished with lactic acid fermentation. An extensive strain screening of 70 lactic acid bacteria from 16 genera was performed to identify suitable strains to transform substrates made from lupines and faba beans into refreshing beverages and to improve their sensory characteristics. By analyzing carbohydrate utilization, production of organic acids and aroma compounds, and sensory appearance, 22 strains for lupine and eight strains for faba bean were preselected. Subsequently, the most suitable strains (five for lupine and three for faba beans) were identified by a trained sensory panel, and finally their growth kinetics were discussed. Generally, the aroma profile varied highly with the utilized strain. However, by selecting suitable strains, the beany impression can be highly reduced and pleasant aroma impressions (e.g., fruity and buttermilk) can be added. Most strikingly, it was proven that using germinated lupines and faba beans instead of raw ones can bypass the usual growth restriction, and the strain selection can be focused exclusively on sensory aspects. This opens the option to use strains usually excluded for the fermentation of legumes due to their lack of utilization of the legume-typical α-galactosides.

Ritter, S., Enßling, S., Becker, T.: Identification of key aroma compounds of faba beans (Vicia faba) and their development during germination - a SENSOMICS approach. Food Chemistry (435), 2024

doi:10.1016/j.foodchem.2023.137610

Faba beans are a promising source of valuable plant protein. However, their aroma impression is often a hindrance for the use in a broad range of food products. To develop mitigation strategies, a deeper insight into the faba bean aroma is required. Therefore, for the first time, the SENSOMICS concept was applied. First, 52 aroma active compounds in raw and malted faba beans were identified and semi-quantitatively preselected by aroma extract dilution analysis. Afterwards, the aroma compounds were quantified, odor activity values were calculated, and the 17 prominent odors were selected and used in the reconstitution of the faba bean aroma. Seven statistically significant key aroma compounds 3-methylbutanoic acid, (E)-non-2-enal, hexanal, methional, 3-methylbutanal, sotolon, and 2-methylbutan-1-ol were identified in omission experiments. Finally, their development upon malting was studied. To conclude, by knowing the key aroma compounds, specific mitigation strategies can be developed, which facilitates the broader use of faba beans.

Ritter, S., Gastl, M., & Becker, T. Impact of Germination on the Protein Solubility and Antinutritive Compounds of Lupinus angustifolius and Vicia faba in the Production of Protein-Rich Legume-Based Beverages. Journal of Agricultural and Food Chemistry (2023)
https://doi.org/10.1021/acs.jafc.3c01249

Lupines and faba beans are protein-rich legumes, which can be utilized as a plant-based substitute for animal proteins in human nutrition in general and in the beverage industry in particular. However, their application is hampered by low protein solubility in the acidic pH range and by antinutrients such as flatulence-causing “raffinose family oligosaccharides” (RFOs). Germination is known in the brewing industry for increasing enzymatic activities and mobilizing storage compounds. Therefore, germinations of lupines and faba beans were performed at different temperatures, and their impact on protein solubility, the concentration of free amino acids, and degradation of RFOs, alkaloids, and phytic acid was evaluated. In general, changes were comparable for both legumes but less pronounced in faba beans. Germination depleted the RFOs entirely in both legumes. The protein size distribution was found to be shifted toward smaller fractions, the concentrations of free amino acids multiplied, and protein solubility increased. No substantial reductions in the binding capacity of phytic acid toward iron ions were observed, but a release of free phosphate in lupines was detected. The results prove that germination is an applicable process for refining lupines and faba beans for use not only in refreshing beverages or milk alternatives but also in other food applications.

Ritter, S., Nobis, A., Gastl, M., Becker, T.: Evaluating raffinose family oligosaccharides and their decomposition products by ion chromatography – a method development and advanced repeatability study. Talanta Open 5, 2022

doi:10.1016/j.talo.2022.100086

During the germination of legumes, raffinose family oligosaccharides (RFOs) are decomposed into mono- and disaccharides. As legumes are a traditional part of the human nutrition, storage carbohydrates are generally incorporated in the daily meals and can cause flatulence or even abdominal pain. However, their decomposition products can be metabolized without any difficulty. To date, no validated method is available to quantify the main decomposition products, glucose, and galactose simultaneously with the RFOs and the starch decomposition product maltose in a single measurement without derivatization. To provide a suitable method and fill the existing knowledge gap, a highly sensitive ion chromatography method was established. By using an optimized gradient, the separation of the RFOs, namely raffinose, stachyose, and verbascose, from their decomposition products, including glucose, galactose, fructose, and saccharose was accomplished. An advanced repeatability study proved that the method could be used for up to 4 days until the sample or eluent degradation made further measurement unfeasible. To improve the repeatability while avoiding to overload the chromatogram with several internal standards, a mathematical approach was presented to cope with different decomposition characteristics of the analytes and the internal standard. This study presents a modified and validated method allowing the measurement of all relevant carbohydrates in the germination of legumes. By using only a single method, a high number of samples can be processed. Therefore, a deeper and more detailed insight into the changes in the carbohydrate spectrum during the germination of legumes becomes feasible.

Ritter, S., Gastl, M., Becker, T.: The modification of volatile and nonvolatile compounds in lupines and faba beans by substrate modulation and lactic acid fermentation to facilitate their use for legume‐based beverages — A review. Comprehensive Reviews in Food Science and Food Safety, 2022, 1-38

doi:10.1111/1541-4337.13002

Lupines and faba beans are promising ingredients for the beverage industry. They contain high amounts of protein and can be grown in different climate zones and agricultural areas. Therefore, these legumes appear as ideal raw material for vegan, functional, and sustainable beverages. Nevertheless, the sensory characteristic of legumes is generally not accepted in beverages. Therefore, the market contribution of legume-based beverages is currently only marginal. This review highlights known major flavor aspects of lupines and faba beans and the possibilities to improve these by germination, heat treatment, enzymatic treatment, and subsequent lactic acid fermentation. First, the main aroma and taste compounds are described. Thereby, the “beany” aroma is identified as the most relevant off-flavor. Second, the nutrients and antinutrients of these legumes regarding to their use as food and as substrate for lactic acid fermentation are reviewed, and possibilities to modulate the substrate are summarized. Finally, the modification of the sensory profile by lactic acid fermentation is outlined. To conclude, it seems likely that the nutritional and flavor attributes in legume-based beverages can be improved by a combined process of substrate modulation and fermentation. In a first step, antinutrients should be decomposed and proteins solubilized while transforming the solid grains into a liquid substrate. Due to such substrate modulation, a broader variety of strains could be employed and the fermentation could be based exclusively on their impact on the flavor. By applying the concept of combining a substrate modulation with a subsequent fermentation, the use of legumes in beverages could be facilitated and new products like vegan, protein-rich, refreshing beverages could be marketed.

17. Oktober 2025

Fabian Lauck

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