Biology subjects

Lievens, B.

Publications and source records attributed to Lievens, B..

5 recordsLinked to original sources

bioRxiv2022

Development of a tractable model system to mimic wood-ageing of beer on a lab scale

Wood-ageing of conventionally fermented beers is gaining increased attention in the production of sour beers with a noteworthy balance between sourness, wood aroma and flavour complexity. Besides the extraction of wood-derived compounds into the beer, wood-aged sours owe their layered flavour profile to the activity of a variety of wild microorganisms that reside in the barrels or that emerge from the brewing or maturation environment. However, until now wood-ageing of craft beers largely remains a process of trial and error that often generates unexpected or undesirable results. Therefore, to better understand the process and develop control strategies to improve the consistency, predictability and overall quality of the resulting beer, more insight is needed into the interactions between the wood, the microorganisms and the maturing beer. Nevertheless, as studying these interactions on an industrial scale is highly challenging, the objective of this study was to develop a reproducible and easy-to-manipulate experimentally tractable system that can be used to study wood-ageing of beer on a lab scale. Barrel-ageing was mimicked in a 0.5 liter glass jar filled with beer and closed off by a wooden disk. Furthermore, the system was equipped with a synthetic community composed of four bacterial species (Acetobacter malorum, Gluconobacter oxydans, Lactobacillus brevis and Pediococcus damnosus) and four fungal species (Brettanomyces bruxellensis, Candida friedrichii, Pichia membranifaciens and Saccharomyces cerevisiae) that represented key microbes previously identified in wood-ageing experiments with 225-liter barrels. In order to test the hypothesis that the barrel-ageing process of beer can be replicated in the simplified in-vitro system, the system was subjected to 60 days of ageing and microbial community dynamics and beer chemistry were compared with a 38-week industrial barrel-ageing experiment using the same beer. Beer samples were collected at regular time points and subjected to both qPCR assays targeting the eight selected species and chemical analysis. Results revealed that in vitro ageing showed similar trends in the temporal dynamics of the microbial populations and beer chemistry as those observed during 38-weeks of barrel-ageing in 225-liter barrels. Furthermore, results were found to be highly reproducible. Altogether, the in-vitro system was found to be a robust and reproducible system that has great potential to perform more in-depth research about the intricate interactions between microbes, wood and maturing beer and to develop control strategies to improve the consistency, predictability and overall quality of the resulting beer.

microbiology↗

bioRxiv2022

Beer ethanol and iso-α-acid level affect microbial community establishment and beer chemistry throughout wood maturation of beer

Sour beers produced by barrel-aging of conventionally fermented beers are becoming increasingly popular. However, as the intricate interactions between the wood, the microbes and the beer are still unclear, wood maturation often leads to inconsistent end products with undesired sensory properties. Previous research on industrial barrel-aging of beer suggests that beer parameters like the ethanol content and bitterness play an important role in the microbial community composition and beer chemistry, but their exact impact still remains to be investigated. In this study, an experimentally tractable lab-scale system based on an in-vitro community of four key bacteria (Acetobacter malorum, Gluconobacter oxydans, Lactobacillus brevis and Pediococcus damnosus) and four key yeasts (Brettanomyces bruxellensis, Candida friedrichii, Pichia membranifaciens and Saccharomyces cerevisiae) that are consistently associated with barrel-aging of beer, was used to test the hypotheses that beer ethanol and bitterness impact microbial community composition and beer chemistry. Experiments were performed using different levels of ethanol (5.2 v/v%, 8 v/v% and 11 v/v%) and bitterness (13 ppm, 35 ppm and 170 ppm iso--acids), and beers were matured for 60 days. Samples were taken after 0, 10, 20, 30 and 60 days to monitor population densities and beer chemistry. Results revealed that all treatments and the maturation time significantly affected the microbial community composition and beer chemistry. More specifically, the ethanol treatments obstructed growth of L. brevis and G. oxydans and delayed fungal growth. The iso--acid treatments hindered growth of L. brevis and stimulated growth of P. membranifaciens, while the other strains remained unaffected. Beer chemistry was found to be affected by higher ethanol levels, which led to an increased extraction of wood-derived compounds. Furthermore, the distinct microbial communities also induced changes in the chemical composition of the beer samples, leading to concentration differences in beer- and wood-derived compounds like 4-ethyl guaiacol, 4-ethyl phenol, cis-oak lactone, vanillin, furfural and 5-methyl furfural. Altogether, our results indicate that wood-aging of beer is affected by biotic and abiotic parameters, influencing the quality of the final product. Additionally, this work provides a new, cost-effective approach to study the production of barrel-aged beers based on a simplified microbial community model.

microbiology↗

bioRxiv2022

Meta-analysis of the black soldier fly (Hermetia illucens) microbiota based on 16S rRNA gene amplicon sequencing

Black soldier fly larvae (BSFL) belong to the most widely reared insect species as an alternative protein source at industrial scale. Bacteria in the larval gut can provide benefits for the animal, though some bacteria can also be pathogenic for the insect. Accurate characterization of the BSFL microbiota is important for the production of BSFL in terms of yield and microbiological safety. In this study, 16S ribosomal RNA gene sequence data sets from 11 studies were re-analysed to gain better insights in the BSFL gut microbiota, potential factors that influence their composition, and differences between the gut and the whole larvae microbiota. A core gut microbiota was found consisting of members of Enterococcus, Klebsiella, Morganella, Providencia, and Scrofimicrobium. Further, the factors "Study", "Age" and "Feed" significantly affected the microbiota gut composition. When compared to whole larvae, a significantly lower number of observed zero-radius Operational Taxonomic Units and a lower diversity was found for gut samples, suggesting that the larvae harboured additional microbes on their cuticle or in the insect body. Universal choices in insect sample type, primer selection and bio-informatics can strengthen future meta-analyses and improve our understanding of the BSFL gut microbiota towards the optimization of insect production.

microbiology↗

bioRxiv2020

Microbiological safety of industrially reared insects for food: Identification of bacterial endospores and targeted detection of foodborne viruses

Edible insects are characterised by high microbial numbers of which the bacterial endospores fraction can survive (thermal) processing. It is unknown, however, which bacterial species occur as endospore in edible insects and what impact they have on food safety. Additionally, edible insects have never been explored for the presence of foodborne viruses so far. In this study, we found that the bacterial endospore fraction in a collection of mealworm and cricket samples obtained from commercial insect producers can comprise a large amount of Bacillus cereus group members that can pose insect or human health risks. Monitoring and effective mitigation of these risks are urged. By contrast, none of the foodborne viruses hepatitis A virus, hepatitis E virus and norovirus genogroup II were detected in the sample collection. Therefore, food safety risks originating from these viral pathogens can be concluded to be low.

microbiology↗

bioRxiv2019

Comparative genome analysis of Lactobacillus mudanjiangensis, an understudied member of the Lactobacillus plantarum group

The genus Lactobacillus is known to be extremely diverse and consists of different phylogenetic groups that show a diversity roughly equal to the expected diversity of a typical bacterial genus. One of the most prominent phylogenetic groups within this genus is the Lactobacillus plantarum group which contains the understudied Lactobacillus mudanjiangensis species. Before this study, only one L. mudanjiangensis strain, DSM 28402T, was described but without whole-genome analysis. In this study, three strains classified as L. mudanjiangensis, were isolated from three different carrot juice fermentations and their whole-genome sequence was determined, together with the genome sequence of the type strain. The genomes of all four strains were compared with publicly available L. plantarum group genome sequences. This analysis showed that L. mudanjiangensis harbored the second largest genome size and gene count of the whole L. plantarum group. In addition, all members of this species showed the presence of a gene coding for a putative cellulose-degrading enzyme. Finally, three of the four L. mudanjiangensis strains studied showed the presence of pili on scanning electron microscopy (SEM) images, which were linked to conjugative gene regions, coded on plasmids in at least two of the strains studied. Author summaryLactobacillus mudanjiangensis is an understudied species within the Lactobacillus plantarum group. Since its first description, no other studies have reported its isolation. Here, we present the first four genome sequences of this species, which include the genome sequence of the type strain and three new L. mudanjiangensis strains isolated from fermented carrot juice. The genomes of all four strains were compared with publicly available L. plantarum group genome sequences. We found that this species harbored the second largest genome size and gene count of the whole L. plantarum group. Furthermore, we present the first scanning electron microscopy (SEM) images of L. mudanjiangensis, which showed the formation of pili in three strains that we linked to genes related to conjugation. Finally, we found the presence of a unique putative cellulose-degrading enzyme, opening the door for different industrial applications of these Lactobacillus strains.

microbiology↗