Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Understanding and governing learning in sustainability transitions : A review
Mierlo, Barbara van; Beers, Pieter J. - \ 2018
Environmental Innovation and Societal Transitions (2018). - ISSN 2210-4224 - 15 p.
Collaborative learning - Interactive learning - Organizational learning - Social learning - Sustainability transition

Many transitions scholars underscore the importance of learning in sustainability transitions, but the associated learning processes have hardly been conceptualised. The diverse, well-established research fields related to learning are broadly ignored or loosely applied. In this paper, we systematically explore four interesting learning traditions in terms of their value for gaining an in-depth understanding of learning in sustainability transitions and their relevance for fostering learning, by connecting them to key features of transitions. The selected learning traditions from different disciplinary backgrounds provide valuable insights. None of them sufficiently addresses the complexity of transitions. They include, however, a diversity of relevant learning contexts. We conclude that they have value for investigating new areas such as learning in socio-technological regimes and in later phases of a transition, while enlightening forms of learning that have not yet been fully recognised in transition studies, such as superficial learning, unlearning, and learning to resist change.

CRISPR-Cas genome engineering of esterase activity in Saccharomyces cerevisiae steers aroma formation
Dank, Alexander ; Smid, Eddy J. ; Notebaart, Richard A. - \ 2018
BMC Research Notes 11 (2018)1. - ISSN 1756-0500 - 1 p.
Aroma - CRISRP-Cas9 - Esterase - Saccharomyces cerevisiae

OBJECTIVE: Saccharomyces cerevisiae is used worldwide for the production of ale-type beers. This yeast is responsible for the production of the characteristic fruity aroma compounds. Esters constitute an important group of aroma active secondary metabolites produced by S. cerevisiae. Previous work suggests that esterase activity, which results in ester degradation, may be the key factor determining the abundance of fruity aroma compounds. Here, we test this hypothesis by deletion of two S. cerevisiae esterases, IAH1 and TIP1, using CRISPR-Cas9 genome editing and by studying the effect of these deletions on esterase activity and extracellular ester pools.

RESULTS: Saccharomyces cerevisiae mutants were constructed lacking esterase IAH1 and/or TIP1 using CRISPR-Cas9 genome editing. Esterase activity using 5-(6)-carboxyfluorescein diacetate (cFDA) as substrate was found to be significantly lower for ΔIAH1 and ΔIAH1ΔTIP1 mutants compared to wild type (WT) activity (P < 0.05 and P < 0.001, respectively). As expected, we observed an increase in relative abundance of acetate and ethyl esters and an increase in ethyl esters in ΔIAH1 and ΔTIP1, respectively. Interestingly, the double gene disruption mutant ΔIAH1ΔTIP1 showed an aroma profile comparable to WT levels, suggesting the existence and activation of a complex regulatory mechanism to compensate multiple genomic alterations in aroma metabolism.

Simultaneous determination of aflatoxin B1, fumonisin B1 and deoxynivalenol in beer samples with a label-free monolithically integrated optoelectronic biosensor
Pagkali, Varvara ; Petrou, Panagiota S. ; Makarona, Eleni ; Peters, Jeroen ; Haasnoot, Willem ; Jobst, Gerhard ; Moser, Isabella ; Gajos, Katarzyna ; Budkowski, Andrzej ; Economou, Anastasios ; Misiakos, Konstantinos ; Raptis, Ioannis ; Kakabakos, Sotirios E. - \ 2018
Journal of Hazardous Materials 359 (2018). - ISSN 0304-3894 - p. 445 - 453.
Aflatoxin B - Beer - Deoxynivalenol - Fumonisin B - Monolithically integrated Mach-Zehnder interferometers

A label-free optical biosensor for the fast simultaneous determination of three mycotoxins, aflatoxin B1 (AFB1), fumonisin B1 (FB1) and deoxynivalenol (DON), in beer samples is presented. The biosensor is based on an array of ten Mach-Zehnder interferometers (MZIs) monolithically integrated along with their respective broad-band silicon light sources onto a single chip. Multi-analyte determination is accomplished by functionalizing the sensing arms of individual MZIs with mycotoxin-protein conjugates. Assay is performed by pumping over the chip mixtures of calibrators or samples with a mixture of specific monoclonal antibodies, followed by reaction with a secondary anti-mouse IgG antibody. Reactions are monitored in real-time by continuously recording the MZI output spectra, which are then subjected to Discrete Fourier Transform to convert spectrum shifts to phase shifts. The detection limits achieved for AFB1, FB1 and DON were 0.8, 5.6 and 24 ng/ml, respectively, while the assay duration was 12 min. Recovery values ranging from 85 to 115% were determined in beer samples spiked with known concentrations of the three mycotoxins. In addition, beers of different types and origin were analysed with the biosensor developed and the results were compared with those provided by established laboratory methods, further supporting the accuracy of the proposed device.

Global-change effects on early-stage decomposition processes in tidal wetlands-implications from a global survey using standardized litter
Mueller, Peter ; Schile-Beers, Lisa M. ; Mozdzer, Thomas J. ; Chmura, Gail L. ; Dinter, Thomas ; Kuzyakov, Yakov ; Groot, Alma V. de; Esselink, Peter ; Smit, Christian ; Alpaos, Andrea D'; Ibáñez, Carles ; Lazarus, Magdalena ; Neumeier, Urs ; Johnson, Beverly J. ; Baldwin, Andrew H. ; Yarwood, Stephanie A. ; Montemayor, Diana I. ; Yang, Zaichao ; Wu, Jihua ; Jensen, Kai ; Nolte, Stefanie - \ 2018
Biogeosciences 15 (2018)10. - ISSN 1726-4170 - p. 3189 - 3202.

Tidal wetlands, such as tidal marshes and mangroves, are hotspots for carbon sequestration. The preservation of organic matter (OM) is a critical process by which tidal wetlands exert influence over the global carbon cycle and at the same time gain elevation to keep pace with sea-level rise (SLR). The present study assessed the effects of temperature and relative sea level on the decomposition rate and stabilization of OM in tidal wetlands worldwide, utilizing commercially available standardized litter. While effects on decomposition rate per se were minor, we show strong negative effects of temperature and relative sea level on stabilization, as based on the fraction of labile, rapidly hydrolyzable OM that becomes stabilized during deployment. Across study sites, OM stabilization was 29% lower in low, more frequently flooded vs. high, less frequently flooded zones. Stabilization declined by ∼ 75% over the studied temperature gradient from 10.9 to 28.5°C. Additionally, data from the Plum Island long-term ecological research site in Massachusetts, USA, show a pronounced reduction in OM stabilization by &gt; 70% in response to simulated coastal eutrophication, confirming the potentially high sensitivity of OM stabilization to global change. We therefore provide evidence that rising temperature, accelerated SLR, and coastal eutrophication may decrease the future capacity of tidal wetlands to sequester carbon by affecting the initial transformations of recent OM inputs to soil OM.

Tracking polysaccharides through the brewing process
Fangel, Jonatan U. ; Eiken, Jens ; Sierksma, Aafje ; Schols, Henk A. ; Willats, William G.T. ; Harholt, Jesper - \ 2018
Carbohydrate Polymers 196 (2018). - ISSN 0144-8617 - p. 465 - 473.
Beer - Enzymes - Glycan arrays - Malt - Polysaccharides - Wort

Brewing is a highly complex stepwise process that starts with a mashing step during which starch is gelatinized and converted into oligo- and/or monosaccharides by enzymes and heat. The starch is mostly degraded and utilised during the fermentation process, but grains and hops both contain additional soluble and insoluble complex polysaccharides within their cell walls that persist and can have beneficial or detrimental effects on the brewing process. Previous studies have mostly been restricted to analysing the grain and/or malt prior to entering the brewing process, but here we track the fates of polysaccharides during the entire brewing process. To do this, we utilised a novel approach based on carbohydrate microarray technology. We demonstrate the successful application of this technology to brewing science and show how it can be utilised to obtain an unprecedented level of knowledge about the underlying molecular mechanisms at work.

Realistische ecologische doelen voor macrofauna in Noord-Brabantse beken
Verdonschot, R. ; Beers, M. ; Samuels, J. ; Brugmans, B. ; Moeleker, M. ; Scheepens, M. ; Laan, I. van der; Verdonschot, P. - \ 2018
H2O online (2018). - 8
In Noord-Brabant worden de ecologische doelen voor de beekmacrofauna vaak niet gehaald. Om de oorzaken hiervan te identificeren, is onderzocht welke kenmerkende soorten voor langzaam stromende laaglandbeken er in het gebied voorkomen en welke verdwenen of nooit aangetroffen zijn. Er is bekeken welke eisen deze soorten stellen aan hun milieu en er is een inschatting gemaakt van de knelpunten voor deze soorten. Een belangrijk knelpunt was een te hoge organische belasting, maar in de bovenlopen speelde ook een typologisch probleem; trajecten met een van nature beperkt verhang werden steevast slecht gewaardeerd.
Taxonomy of the family Arenaviridae and the order Bunyavirales : update 2018
Maes, Piet ; Alkhovsky, Sergey V. ; Bào, Yīmíng ; Beer, Martin ; Birkhead, Monica ; Briese, Thomas ; Buchmeier, Michael J. ; Calisher, Charles H. ; Charrel, Rémi N. ; Choi, Il Ryong ; Clegg, Christopher S. ; Torre, Juan Carlos de la; Delwart, Eric ; DeRisi, Joseph L. ; Bello, Patrick L. Di; Serio, Francesco Di; Digiaro, Michele ; Dolja, Valerian V. ; Drosten, Christian ; Druciarek, Tobiasz Z. ; Du, Jiang ; Ebihara, Hideki ; Elbeaino, Toufic ; Gergerich, Rose C. ; Gillis, Amethyst N. ; Gonzalez, Jean Paul J. ; Haenni, Anne Lise ; Hepojoki, Jussi ; Hetzel, Udo ; Hồ, Thiện ; Hóng, Ní ; Jain, Rakesh K. ; Jansen van Vuren, Petrus ; Jin, Qi ; Jonson, Miranda Gilda ; Junglen, Sandra ; Keller, Karen E. ; Kemp, Alan ; Kipar, Anja ; Kondov, Nikola O. ; Koonin, Eugene V. ; Kormelink, Richard ; Korzyukov, Yegor ; Krupovic, Mart ; Lambert, Amy J. ; Laney, Alma G. ; LeBreton, Matthew ; Lukashevich, Igor S. ; Marklewitz, Marco ; Markotter, Wanda ; Martelli, Giovanni P. ; Martin, Robert R. ; Mielke-Ehret, Nicole ; Mühlbach, Hans Peter ; Navarro, Beatriz ; Ng, Terry Fei Fan ; Nunes, Márcio Roberto Teixeira ; Palacios, Gustavo ; Pawęska, Janusz T. ; Peters, Clarence J. ; Plyusnin, Alexander ; Radoshitzky, Sheli R. ; Romanowski, Víctor ; Salmenperä, Pertteli ; Salvato, Maria S. ; Sanfaçon, Hélène ; Sasaya, Takahide ; Schmaljohn, Connie ; Schneider, Bradley S. ; Shirako, Yukio ; Siddell, Stuart ; Sironen, Tarja A. ; Stenglein, Mark D. ; Storm, Nadia ; Sudini, Harikishan ; Tesh, Robert B. ; Tzanetakis, Ioannis E. ; Uppala, Mangala ; Vapalahti, Olli ; Vasilakis, Nikos ; Walker, Peter J. ; Wáng, Guópíng ; Wáng, Lìpíng ; Wáng, Yànxiăng ; Wèi, Tàiyún ; Wiley, Michael R. ; Wolf, Yuri I. ; Wolfe, Nathan D. ; Wú, Zhìqiáng ; Xú, Wénxìng ; Yang, Li ; Yāng, Zuòkūn ; Yeh, Shyi Dong ; Zhāng, Yǒng Zhèn ; Zhèng, Yàzhōu ; Zhou, Xueping ; Zhū, Chénxī ; Zirkel, Florian ; Kuhn, Jens H. - \ 2018
Archives of Virology 163 (2018)8. - ISSN 0304-8608 - p. 2295 - 2310.
In 2018, the family Arenaviridae was expanded by inclusion of 1 new genus and 5 novel species. At the same time, the recently established order Bunyavirales was expanded by 3 species. This article presents the updated taxonomy of the family Arenaviridae and the order Bunyavirales as now accepted by the International Committee on Taxonomy of Viruses (ICTV) and summarizes additional taxonomic proposals that may affect the order in the near future.
Development and in-house validation of a rapid and simple to use ELISA for the detection and measurement of the mycotoxin sterigmatocystin
Oplatowska-Stachowiak, Michalina ; Reiring, Claudine ; Sajic, Nermin ; Haasnoot, Willem ; Brabet, Catherine ; Campbell, Katrina ; Elliott, Christopher T. ; Salden, Martin - \ 2018
Analytical and Bioanalytical Chemistry 410 (2018)12. - ISSN 1618-2642 - p. 3017 - 3023.
Enzyme-linked immunosorbent assay - Food safety - Immunoassay - Mycotoxin
Sterigmatocystin (STG) is a highly toxic secondary fungal metabolite structurally closely related to the well-known carcinogenic aflatoxins. Its presence has been reported in grains and grain-based products as well as in other foodstuffs like nuts, green coffee beans, spices, beer and cheese. Due to the lack of suitable data on the occurrence of STG, in 2013, the European Food Safety Authority (EFSA) could not characterise its risk for human health and recommended that more data on STG in food and feed needed to be collected. In order to provide a new tool for the specific detection of STG, a competitive enzyme-linked immunosorbent assay (ELISA) was developed, optimised and validated in this study based on a sensitive monoclonal antibody specific to STG with no cross-reactivity with aflatoxins. The sample preparation method for rice, wheat and maize was based on a modified QuEChERS (quick, easy, cheap, effective, rugged and safe) approach. The assay was validated for the detection of STG in rice, wheat and maize in accordance with the guidelines for validation of semi-quantitative screening methods included in Commission Regulation (EU) 519/2014. The screening target concentration (STC) was set at 1.5 μg/kg. The cutoffs for rice, wheat and maize were 1.2, 1.2 and 1.3 μg/kg and the false suspected rates were 0.34, 1.15 and 0.78%, respectively. Good correlation was found between the results obtained by the STG ELISA and LC-MS/MS method for naturally contaminated rice samples. This validated method can be applied as a sensitive and high-throughput screening for the presence of STG in a range of agricultural commodities. [Figure not available: see fulltext.]
Beers, G. - \ 2017
IoF2020 Internet of Food & Farm - 11 p.
Stripping of Flavour-Active Compounds from Aqueous Food Streams: Effect of Liquid Matrix on Vapour-Liquid Equilibrium in a Beer-like Solution
Ammari, A. ; Schroen, C.G.P.H. - \ 2017
World Academy of Science, Engineering and Technology 11 (2017)11. - ISSN 2070-3740 - 1 p.
In brewing industries, stripping is a downstream process to separate volatiles from beer. Due to physiochemical similarities between flavour components, the selectivity of this method is not favourable. Besides, the presence of non-volatile compounds such as proteins and carbohydrates may affect the separation of flavours due to their retaining properties. By using a stripping column with structured packing coupled with a gas chromatography, in this work, the overall mass transfer coefficient along with their corresponding equilibrium data was investigated for a model solution consist of water, ethanol, ethyl acetate and isoamyl acetate. Static headspace analysis also was employed to derive equilibrium data for flavours in the presence of beer dry matter. As it was expected ethanol and dry matter showed retention properties; however, the effect of viscosity in mass transfer coefficient was discarded due to the fact that the viscosity of solution decreased during stripping. The effect of ethanol and beer dry matter were mapped to be used for designing stripping could.
Fostering business and software ecosystems for large-scale uptake of IoT in food and farming
Verdouw, C.N. ; Wolfert, J. ; Beers, G. ; Sundmaeker, Harald ; Chatzikostas, Grigoris - \ 2017
- 7 p.
The Internet of Things (IoT) is expected to be a real game changer that will drastically improve productivity and sustainability in food and farming. However, current IoT applications in this domain are still fragmentary and mainly used by a small group of early adopters. The Internet of Food and Farm 2020 Large-Scale Pilot (IoF2020) addresses the organizational and technological challenges to overcome this situation by fostering a large-scale uptake of IoT in the European food and farming domain. The heart of the project is formed by a balanced set of multi-actor trials that reflect the diversity of the food and farming domain. Each trial is composed of well-delineated use cases developing IoT solutions for the most relevant challenges of the concerned subsector. The project conducts 5 trials with a total of 19 use cases in arable, dairy, fruits, vegetables and meat production. IoF2020 embraces a lean multi-actor approach that combines the development of Minimal Viable Products (MVPs) in short iterations with the active involvement of various stakeholders. The architectural approach supports interoperability of multiple use case systems and reuse of IoT components across them. Use cases are also supported in developing business and solving governance issues. The IoF2020 ecosystem and collaboration space is established to boost the uptake of IoT in Food and Farming and pave the way for new innovations.
IoT European Large-Scale Pilots – Integration, Experimentation and Testing
Guillén, Sergio ; Sala, Pilar ; Fico, Giuseppe ; Arredondo, María Teresa ; Cano, Alicia ; Posada, Jorge ; Gutiérrez, German ; Palau, Carlos ; Votis, Konstantinos ; Verdouw, C.N. ; Wolfert, J. ; Beers, G. ; Sundmaeker, H. ; Chatzikostas, Grigoris ; Ziegler, Sébastian ; Hemmens, Christopher ; Holst, Marita ; Stahlbröst, Anna ; Scudiero, Lucio ; Reale, C. ; Krco, S. ; Drajic, D. ; Eisenhauer, M. ; Jahn, M. ; Valino, J. ; Gluhak, A. ; Brynskov, M. ; Vermesan, O. ; Fischer, F. ; Lenz, O. - \ 2017
In: Cognitive Hyperconnected Digital Transformation Internet of Things Intelligence Evolution / Vermesan, O., Bacquet, J., River Publishers - ISBN 9788793609112 - p. 221 - 282.
Agricultural sector development : guidelines for Aid & Trade Support in Dutch PSD-partner countries
Westenbrink, Geert ; Beers, George ; Joosten, Frank ; Dijkxhoorn, Youri ; Broek, Joep van den; Lee, Jan van der; Groot, Nico de - \ 2017
The Hague : Ministry of Agriculture, Nature and Food Quality of the Netherlands. - 41
Onconventionele gisten: de sleutel tot bierinnovatie?
Smid, Eddy - \ 2017

Vandaag de dag zijn laag-alcoholische dranken en alcoholvrije bieren populairder dan ooit. Hierdoor wordt het aanbod van speciale soorten bier steeds groter. Dit maakt ook de weg vrij voor de ontwikkeling van smaakvolle, fruitige biersoorten met een laag alcoholpercentage.

Low-alcohol beverages and alcohol-free beers are more trending than ever before. Conventionally, brewers’ yeast is used as pure culture to convert the wort sugars into alcohol, carbon dioxide and flavors. In her PhD research project, Irma van Rijswijck investigated the potential of non-conventional yeast species using various inoculation strategies.

Brewing fruity light beers using a different kind of yeast
Rijswijck, Irma van - \ 2017

Specialty beers are becoming increasingly popular, but often contain a relatively high alcohol percentage. By using different kinds of yeast, it is possible to brew low-alcohol beer, with a rich and fruity taste. A Wageningen PhD candidate, Irma van Rijswijck, discovered this.

Reframing the future : the role of reflexivity in governance networks in sustainability transitions
Sol Ir, Jifke ; Wal, Merel M. van der; Beers, Pieter Jelle ; Wals, Arjen - \ 2017
Environmental Education Research (2017). - ISSN 1350-4622 - p. 1 - 23.
commitment - reflexivity - reframing - regional governance networks - social learning - Sustainability - transitions - trust
Regional sustainability networks in the Netherlands are rooted in regional culture and have an emphasis on social learning and effective collaboration between multiple actors. The national ‘Duurzaam Door’ (Moving Forward Sustainably) Policy Programme regards these networks as generative governance arrangements where new knowledge, actions and relations can co-evolve together with new insights in governance and learning within sustainability transitions. In order to understand the dynamics of the learning in these networks we have monitored emergent properties of social learning between 2014 and 2016. Our focus is particularly on the interrelated role of trust, commitment, reframing and reflexivity. Our aim is to better understand the role and the dynamics of these emergent properties and to see which actors and roles can foster the effectiveness of social learning in regional transitions towards more sustainable ways of living. We used a retrospective analysis with Reflexive Monitoring in Action (RMA), which we combined with the Most Significant Change approach. We found that reflexivity in particular is a critical property at moments that can make or break the process.
Performance of non-conventional yeasts in co-culture with brewers’ yeast for steering ethanol and aroma production
Rijswijck, Irma M.H. van; Wolkers - Rooijackers, Judith C.M. ; Abee, Tjakko ; Smid, Eddy J. - \ 2017
Microbial Biotechnology 10 (2017)6. - ISSN 1751-7907 - p. 1591 - 1602.

Increasing interest in new beer types has stimulated the search for approaches to extend the metabolic variation of brewers’ yeast. Therefore, we tested two approaches using non-conventional yeast to create a beer with lower ethanol content and a complex aroma bouquet. First, the mono-culture performance was monitored of 49 wild yeast isolates of Saccharomyces cerevisiae (16 strains), Cyberlindnera fabianii (9 strains) and Pichia kudriavzevii (24 strains). Interestingly, both C. fabianii and P. kudriavzevii isolates produced relatively more esters compared with S. cerevisiae isolates, despite their limited fermentation capacity. Next, one representative strain of each species (Sc131, Cf65 and Pk129) was applied as co-culture with brewers’ yeast (ratio 1:1). Co-cultures with Cf65 and Pk129 resulted in a beer with lower alcohol content (3.5, 3.8 compared with 4.2% v/v) and relatively more esters. At higher inoculum ratios of Cf65 over brewers’ yeast, growth inhibition of brewers’ yeast was observed, most likely caused by competition for oxygen between brewers’ yeast and Cf65 resulting in a reduced level of ethanol and altered aroma profiles. With this study, we demonstrate the feasibility of using non-conventional yeast species in co-cultivation with traditional brewers’ yeast to tailor aroma profiles as well as the final ethanol content of beer.

Mycotoxin profiling of 1000 beer samples with a special focus on craft beer
Peters, Jeroen ; Dam, Ruud van; Doorn, Ronald van; Katerere, David ; Berthiller, Franz ; Haasnoot, Willem ; Nielen, Michel W.F. - \ 2017
PLoS One 12 (2017)10. - ISSN 1932-6203 - 27 p.

Currently beer is booming, mainly due to the steady rise of craft breweries worldwide. Previous surveys for occurrence of mycotoxins in beer, were mainly focussed on industrial produced beer. The present survey reports the presence of mycotoxins in craft beer and how this compares to industrial produced beer. More than 1000 beers were collected from 47 countries, of which 60% were craft beers. A selection of 1000 samples were screened for the presence of aflatoxin B1, ochratoxin A (OTA), zearalenone (ZEN), fumonisins (FBs), T-2 and HT-2 toxins (T-2 and HT-2) and deoxynivalenol (DON) using a mycotoxin 6-plex immunoassay. For confirmatory analysis, a liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed and applied. The 6-plex screening showed discrepancies with the LC-MS/MS analysis, possibly due to matrix interference and/or the presence of unknown mycotoxin metabolites. The major mycotoxins detected were DON and its plant metabolite deoxynivalenol-3-β-D-glucopyranoside (D3G). The 6-plex immunoassay reported the sum of DON and D3G (DON+D3G) contaminations ranging from 10 to 475 μg/ L in 406 beers, of which 73% were craft beers. The popular craft beer style imperial stout, had the highest percentage of samples suspected positive (83%) with 29% of all imperial stout beers having DON+D3G contaminations above 100 μg/L. LC-MS/MS analysis showed that industrial pale lagers from Italy and Spain, predominantly contained FBs (3-69 μg/L). Besides FBs, African traditional beers also contained aflatoxins (0.1-1.2 μg/L). The presence of OTA, T-2, HT-2, ZEN, β-zearalenol, 3/15-acetyl-DON, nivalenol and the conjugated mycotoxin zearalenone 14-sulfate were confirmed in some beers. This study shows that in 27 craft beers, DON+D3G concentrations occurred above (or at) the Tolerable Daily Intake (TDI). Exceeding the TDI, may have a health impact. A better control of brewing malts for craft beer, should be put in place to circumvent this potential problem.

Co-cultivation of non-conventional yeast with Saccharomyces cerevisiae to increase the aroma complexity of fermented beverages
Rijswijck, Irma M.H. van - \ 2017
University. Promotor(en): Eddy Smid; Tjakko Abee. - Wageningen : Wageningen University - ISBN 9789463436250 - 145

Yeast are used as workhorses to convert hopped wort into beer. Conventionally, such yeasts belong to the genus Saccharomyces and most research on fermentation of wort for the production of beer has focussed on the species Saccharomyces cerevisiae and Saccharomyces pastorianus. Recently, there is an increasing interest in unravelling features of non-conventional yeast species for beer innovation. In this thesis, features of yeast isolates belonging to the species: Cyberlindnera fabianii, Pichia kudriavzevii and S. cerevisiae (all isolated from fermented masau (Ziziphus mauritiana) fruits in Zimbabwe), were studied with focus on aroma production. Additionally, a novel approach was used to apply these yeasts in co-cultivation with Brewers’ yeast (S. cerevisiae) for beer innovation.

The characteristics and quality of the beer are mainly determined by aroma compounds in the final product such as esters, alcohols, aldehydes and acids. Yeast use various metabolic pathways such as glycolysis, the fermentative pathway, the tricarboxylic acid (TCA) cycle and the Ehrlich pathway to produce aroma compounds or the precursors for the synthesis thereof (Chapter 1). Among the aroma compounds, esters are of major importance, especially since they are perceived by the human olfactory system at very low concentrations. In general, esters are desirable compounds in beers due to their fruity flavour. Examples are isoamyl acetate (banana), isobutyl acetate (fruity, sweet), phenylethyl acetate (rose, apple, honey), ethyl acetate (sweet pear), ethyl hexanoate (apple, aniseed) and ethyl octanoate (sour apple). Together with an extensive range of other volatile organic compounds (VOCs) these compounds were previously profiled using headspace solid-phase-micro-extraction gas-chromatography mass-spectrometry (GCMS). Interestingly, comparative profiling of aromas showed that C. fabianii produces significantly higher amounts of isoamyl acetate and ethyl acetate compared to S. cerevisiae.

It has been suggested in literature that products of the Ehrlich pathway, so called “fusel alcohols”, can function as signalling molecules for invasive growth upon nitrogen limitation. This suggested that nutrient limitation could affect growth performance and production of aroma compounds. Therefore, in Chapter 2, the metabolic and morphological response of S. cerevisiae, C. fabianii and P. kudriavzevii was analysed upon nitrogen and/or glucose limitation on semi-solid (agar) media. All three yeasts showed a change in growth mode upon nitrogen and/or glucose limitation. Scanning electron microscopy was used to unravel the cell organisation of C. fabianii and P. kudriavzevii grown under nitrogen limitation. This revealed the power of cell-cell adhesion for penetrative growth and the formation of meta-filaments or pseudo-hyphae to extend the cell surface area. Such changes in growth mode may be of relevance for solid-state fermentation processes, such as fruit fermentations, by enhanced substrate penetration of yeast. Notably, a significant increase in the production of esters (ethyl acetate, ethyl propanoate, isobutyl acetate and isopentyl acetate) by C. fabianii and P. kudriavzevii was found under conditions of nitrogen limitation. Understanding the relationship between nitrogen limitation and ester formation gives more insight into the ability to steer ester formation by nutrient availability in wort fermentations.

The amount and type of esters are important determinants of the final flavour characteristics of the beer. Therefore, the diversity in ester production between the three yeast species was investigated by studying enzymatic reactions involved in the production (synthesis) of esters and their degradation (hydrolysis) and to link this to volatile organic compound profiles (Chapter 3). The amount and type of esters depends on substrate availability and a combination of enzyme activities supporting the synthesis and hydrolysis of the different esters formed. Esters are generally formed by a condensation reaction of an alcohol with ac(et)yl CoA by a so-called alcohol acetyltranferase (AATse). The products formed can generally be subdivided into two groups; acetate esters and medium chain fatty acid (MCFA) esters. Alcohols are formed by reduction of aldehydes by alcohol dehydrogenases (ADH) using either the fermentative or Ehrlich pathway. Comparative analysis of the specific ADHs and acetate ester hydrolysing activity and subsequently linking these data with the distinct aroma profiles of the three yeasts revealed that the acetate ester hydrolysing activity is a key step in determining the final pool size of acetate esters found in the fermentation broths (Chapter 3). Under the experimental conditions, C. fabianii showed the lowest acetate ester hydrolysing activity correlating with higher extracellular levels of acetate esters indicating the suitability of this yeast for use in co-cultures with brewers’ yeast with the objective to enable the enrichment of acetate esters in the fermentation process (Chapters 4 and 5).

Nowadays, there is large interest of consumers in specialty beers such as beers low in alcohol (health awareness) and/or richer is fruity flavours (specialty beers), and this has significantly stimulated the quest for new methods, practices and yeast strains to produce such beers. In chapter 4 an innovative approach is described using co-cultivations of brewers’ yeast and C. fabianii to steer wort fermentation performance. Various ratios of brewers’ yeast over C. fabianii were inoculated in wort. A dose response relationship was observed, where a higher initial dose of C. fabianii leads to lower alcohol production and a more complex aroma bouquet. Interestingly, specific esters, i.e. ethyl acetate (sweet pear), ethyl octanoate (sour apple), ethyl decanoate (waxy, sweet apple), ethyl 9-decenoate (fruity, fatty) and ethyl dodecanoate (fruity, waxy), were found in higher levels in co-cultivation compared to both mono-cultivations indicating metabolic interactions. The reduced ethanol production in the co-culture could be explained by inhibition of Brewers’ yeast performance by C. fabianii in the co-cultivations. Further investigations revealed that this growth inhibition is caused by competition for oxygen between brewers’ yeast and C. fabianii. Depletion of oxygen caused inhibition of growth of brewers’ yeast since it needs oxygen to synthesize ergosterol that is required for cell membrane synthesis under anaerobic conditions (Chapter 4).

The interaction between brewers’ yeast and C. fabianii in co-cultivation can be described using dynamic modelling (Chapter 5). A dynamic model was developed based on brewers’ yeast and C. fabianii in mono-cultivation and fitted to experimental data. The two models were combined and the same parameter settings were used to predict the fermentation outcome of brewers’ yeast and C. fabianii in co-cultivation. The model was experimentally validated using inoculation ratios of 1:10 and 1:100 brewers’ yeast over C. fabianii. Additionally, the use of dynamic modelling supported the hypothesis that competition for oxygen between brewers’ yeast and C. fabianii results in inhibition of brewers’ yeast fermentation performance. Interestingly, prediction of aroma formation in co-cultivation, especially that of specific esters, appeared to be more challenging due to metabolic interactions resulting in MCFA-esters contributing to fruity aromas, and this aspect requires further study.

The results and findings obtained in the experimental chapters (Chapter 2-5) are further discussed in Chapter 6. Unravelling features of non-conventional yeast generates novel opportunities for beer innovation. Application of C. fabianii in co-cultivation with brewers’ yeast in wort fermentation offers a novel approach in product innovation resulting in low alcohol beers with enriched aroma bouquet . Finally, the developed dynamic model may be used to predict fermentation outcomes of brewers’ yeast with other non-conventional yeast species.

XYLEM NAC DOMAIN1, an angiosperm NAC transcription factor, inhibits xylem differentiation through conserved motifs that interact with RETINOBLASTOMA-RELATED
Zhao, Chengsong ; Lasses, Theres ; Bako, Laszlo ; Kong, Danyu ; Zhao, Bingyu ; Chanda, Bidisha ; Bombarely, Aureliano ; Cruz-Ramírez, Alfredo ; Scheres, Ben ; Brunner, Amy M. ; Beers, Eric P. - \ 2017
New Phytologist 216 (2017)1. - ISSN 0028-646X - p. 76 - 89.
Arabidopsis thaliana - Angiosperm - Differentiation - LXCXE - NAC domain - Retinoblastoma - Xylem

The Arabidopsis thaliana gene XYLEM NAC DOMAIN1 (XND1) is upregulated in xylem tracheary elements. Yet overexpression of XND1 blocks differentiation of tracheary elements. The molecular mechanism of XND1 action was investigated. Phylogenetic and motif analyses indicated that XND1 and its homologs are present only in angiosperms and possess a highly conserved C-terminal region containing linear motifs (CKII-acidic, LXCXE, E2FTD-like and LXCXE-mimic) predicted to interact with the cell cycle and differentiation regulator RETINOBLASTOMA-RELATED (RBR). Protein-protein interaction and functional analyses of XND1 deletion mutants were used to test the importance of RBR-interaction motifs. Deletion of either the LXCXE or the LXCXE-mimic motif reduced both the XND1-RBR interaction and XND1 efficacy as a repressor of differentiation, with loss of the LXCXE motif having the strongest negative impacts. The function of the XND1 C-terminal domain could be partially replaced by RBR fused to the N-terminal domain of XND1. XND1 also transactivated gene expression in yeast and plants. The properties of XND1, a transactivator that depends on multiple linear RBR-interaction motifs to inhibit differentiation, have not previously been described for a plant protein. XND1 harbors an apparently angiosperm-specific combination of interaction motifs potentially linking the general differentiation regulator RBR with a xylem-specific pathway for inhibition of differentiation.

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