Research

With 31.9 million tons in 2023, Germany is one of the world's leading milk producers. Exports of dairy products are very important for the German dairy industry. It should be noted that the goods are subject to long transit times and cold storage periods, which can affect the quality and spoilage of the products. The economic damage caused by spoilage organisms in the milk processing sector amounts to between 25 and 30% worldwide.

It can be assumed that a significant proportion of the economic damage is due to contamination with Acinetobacter spp. A project funded by the Research Association of the Food Industry (Forschungskreis der Ernährungsindustrie e.V.) in collaboration with the Max Rubner Institute in Kiel aims to derive recommendations for action that will help to reduce contamination of raw milk and counteract the premature spoilage of dairy products. In addition, the rapid test developed is intended to provide a decision-making aid for the utilization of raw milk.

Acinetobacter spp. play a central role in milk and dairy products due to their lipolytic, i.e., fat-degrading, properties. Their influence on the lipid profile can affect the texture, taste, smell, and overall quality and shelf life of the product. Acinetobacter spp. can exhibit high lipolytic activity at lower storage temperatures. The aim of the project is to isolate and identify lipolytically active Acinetobacter spp. relevant to raw milk. In addition, the respective lipases are to be identified and, in the case of particularly abundant representatives, further characterized. The focus is on genetic characterization, lipolytic capacity, and the altered lipid profile resulting from lipolysis. The aim is to identify species that are particularly relevant to spoilage and to analytically evaluate their potential sensory influence. Furthermore, a PCR- or LAMP-PCR-based rapid detection method for species with high lipolytic capacity is to be developed.

The research is being conducted under the auspices of the Cluster of Excellence Understanding Written Artefacts. With the help of metagenome analyses, the microbiota of various manuscripts (preferably from parchment) will be identified and specifically characterized. This research builds on the “Kairouan Manuscript Project,” in which the first manuscripts from the 9th to 11th centuries were examined.

Parchments from various collections and libraries often show signs of damage such as discoloration, warping, or missing sections. The causes of these problems are often attributed to environmental influences and storage conditions, but also to microbial decay. Manuscripts are exposed to various stresses, such as temperature fluctuations and increased water or salt content. However, human handling of manuscripts also influences their condition and structure and forms an individual microbiome on their surface. These microorganisms can break down collagen, the structural protein of skin, and thus negatively affect its structure. Elevated temperatures and proteolysis processes during the production and storage of parchments can trigger and accelerate collagen degradation processes. Since microbial interactions are usually multi-layered and complex, metagenome analyses could provide clues about spoilage agents and general trends.

The hypotheses of this work are as follows:

• When selecting parchment manuscripts from different collections but from the same period and with similar storage conditions, the microbiota can be identified and its composition is comparable. On the other hand, differences in the microbiota can be seen depending on the production, storage, and handling of the manuscripts.
• The microbiome differs at various defect sites from each other and from intact parchment, and the damage is caused by specific microorganisms. Microbial spoilage can be attributed to certain microorganisms, whether bacteria or fungi. Furthermore, these isolates show different expression profiles in transcriptome analysis in the presence of collagen/gelatin and without.
• This deterioration can be simulated using fresh parchment and microbial isolates. Storage conditions are simulated in a controlled long-term test and microbial growth is monitored. The viability of the microorganisms is also checked under a microscope.

Most dyes for the textile industry are made from petrochemicals, which contributes to environmental pollution. On October 1, 2025, the DyeAnotherWay project was launched to remedy this situation. The aim of the project is to use microorganisms to produce renewable and therefore more environmentally friendly dyes. Fourteen universities and industrial partners from across Europe, the US, and Brazil will collaborate in this Marie Skłodowska-Curie Action program, which is funded by the European Union. The project also provides training for 12 doctoral students in the fields of biotechnology, microbiology, chemistry, textile research, and market research. One of these doctoral positions is located in the Food Microbiology working group at the Hamburg School of Food Science in the Department of Chemistry. Here, microorganisms that produce dyes are isolated and identified. The focus will be on black, blue, and red, but in the long term, the entire color palette should be covered, which is particularly interesting for printing on textiles. In addition, testing for applicability in the food sector, which has significantly stricter safety requirements, is also planned. Genome sequencing also provides information for safety assessments and metabolic pathways, enabling the customized production of bio-based dyes on an industrial scale. In collaboration with the other project partners, the aim is to identify dyes that meet the requirements of the textile and food industries.

Current research established the role of crop plants as secondary hosts for human pathogens. It is yet unknown, how these interactions and technologies applied in food processing impact on the virulence of the pathogens. The focus of our research is on the interaction of the human pathogens Listeria monocytogenes with lettuce:

• Pathogens apply similar mechanisms to adhere on/internalize in plant and human hosts. We are studying gene expression patterns of selected pathogens in the presence of plants. The localization of the bacteria on and in the plant will be correlated with the expression of selected marker genes. Genes encoding relevant structures for bacterial adhesion and internalization will be deleted and their function thus confirmed. This will be done by microscopical methods.
• Pathogens react to their host by a change in their transcriptional patterns, which might result in changed virulence. We aim at studying this adaptation of adhered and/or internalized cells in parallel to the reaction of the plant (DualRNASeq), and how that impacts on bacterial virulence. As plants harbor an autochthonous microbiota and as microorganisms interact directly and/or indirectly, this results in a network of interactions rather than in a direct effect.

Suitable strains for targeted food fermentation will be selected by applying “omics” technologies

This project is based on a finished FEI-project (AiF 19688 N). Lactococcus lactis is industrially applied as a starter organism for dairy fermentations. The strains of this species are genetically diverse because of their plasmidome. Genes encoding key enzymes enabling growth in dairy environments are also plasmid-encoded. It is current knowledge from industrial practice that some strains induce bitterness in fermented dairy products, while others do not. We investigate which genetic determinants in combination with which environmental factors, especially enhanced calcium contents such as usually found in dairy fermentations, induce enhanced bitterness. Based on own results we hypothesize that calcium has an impact on bitter peptide formation which is not due to modified transcription levels of genes encoding the enzymes/proteins of the proteolytic system.

• Fermentation von Fruchtkomponenten mit Exopolysaccharid-bildenden Milchsäurebakterien zur strukturellen Stabilisierung von Fruchtzubereitungen
  01.02.2022 – 31.01.2026, FEI, AiF 22473 N
  https://www.fei-bonn.de/gefoerderte-projekte/projektdatenbank/01if22473n.projekt
  
  
• Zweistufige Fermentation pflanzlicher Rohstoffe zur Herstellung pflanzlicher Alternativen zu Rohwurst und Rohmilchkäse.
  01.09.2021–29.02.2024, FEI, AiF 21931 N
  https://www.fei-bonn.de/gefoerderte-projekte/projektdatenbank/aif-21931-n.projekt
  
  
• Establishing a strong and lasting international training network for innovation in food and juice industries: A 4D-research approach for fruit juice processing (HiStabJuice).
  01.11.2020–28.02.2025, European Union’s Marie Skłodowska-Curie Innovative Training Network (ITN), GA No. 956257
  https://www.histabjuice.eu/
  
  
• Reduktion der Bitterkeit von fermentierten Milchprodukten mit erhöhtem Calciumgehalt durch Selektion geeigneter Starterkulturen - Einfluss milchendogener und exogener Peptidasen.
  01.10.2017–30.09.2020, FEI, AiF 19688 N
  
  
• Technologische und mikrobiologische Ansätze zum Einsatz von Starterkulturen bei der industriellen Rohschinkenherstellung.
  01.05.2013–30.06.2016, FEI, AiF 17687 N
  
  
• Optimierung der mikrobiologischen Qualität und der physiologischen Eigenschaften von verzehrfertigen Blattsalaten und Kräutern mittels innovativer technologischer Verfahren und molekularbiologischer Analysen.
  01.11.2012–31.05.2016, FEI, AiF 17122 N
  
  
• Optimierung von Nachweis und Differenzierung von Salmonella enterica, Cronobacter sakazakii und Bacillus cereus in Milch und Milcherzeugnissen durch den Einsatz von Zellwand-bindenden Phagenproteinen.
  01.11.2010–30.04.2013, FEI, AiF 16756 N
  
  
• Backwaren hergestellt mit Sauerteigen aus Amaranth, Buchweizen und Sorghum unter Verwendung universell einsetzbarer und mikrobiologisch stabiler Sauerteigstarter.
  01.04.2007–30.06.2009, FEI, AiF 15188 N