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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    An approach towards improving safety and hygiene control practices in emerging dairy chains : the case of Tanzania
    Ledo, James - \ 2020
    Wageningen University. Promotor(en): P.A. Luning; K.A. Hettinga, co-promotor(en): W.J.J. Bijman. - Wageningen : Wageningen University - ISBN 9789463955140 - 205
    Production and high throughput quantification of fucoxanthin and lipids in Tisochrysis lutea using single-cell fluorescence
    Gao, Fengzheng ; Teles (Cabanelas, ITD), Iago ; Ferrer-Ledo, Narcís ; Wijffels, René H. ; Barbosa, Maria J. - \ 2020
    Bioresource Technology 318 (2020). - ISSN 0960-8524
    Chlorophyll - Fluorescence-activated cell sorting (FACS) - Fucoxanthin - Polar/neutral lipids - Single-cell

    This work aimed to investigate the accumulation of fucoxanthin and lipids in Tisochrysis lutea during growth (N+) and nitrogen-starvation (N−) and to correlate these products with single-cell emissions using fluorescence-activated cell sorting (FACS). Fucoxanthin content decreased 52.94% from N+ to N− in batch cultivation; increased 40.53% as dilution rate changed from 0.16 to 0.55 d−1 in continuous cultivation. Total lipids (N−) were constant (~250 mg/g), but the abundance of neutral lipids increased from 4.87% to 40.63%. Nile red can stain both polar and neutral lipids. However, in vivo, this differentiation is limited due to an overlapping of signals between 600 and 660 nm, caused by neutral lipids concentrations above 3.48% (W/W). Chlorophyll autofluorescence (720 nm) was reported for the first time as a proxy for fucoxanthin (R2 = 0.90) and polar lipids (R2 = 0.98). FACS can be used in high throughput quantification of pigments and lipids and to select and sort cells with high-fucoxanthin/lipids.

    Implications of differences in safety and hygiene control practices for microbial safety and aflatoxin M1 in an emerging dairy chain : The case of Tanzania
    Ledo, James ; Hettinga, Kasper A. ; Kussaga, Jamal B. ; Luning, Pieternel A. - \ 2020
    Food Control 118 (2020). - ISSN 0956-7135
    Critical sampling location - Customised assessment tool - Fresh milk - Microbial contamination - Moulds

    The varying performance of safety and hygiene control practices by chain actors can influence the consistent production of milk of good quality and safety in dairy chains. Therefore, the study aimed to investigate if differences in safety and hygiene control practices translate into distinctions in milk quality and safety at the farm, and to analyse the implications for actors further in the Tanzanian dairy chain. A previously developed diagnostic tool, customised for emerging dairy chains, was applied to assess and differentiate the performance of safety and hygiene control practices of actors from the farm to local retail shops. Based on interviews and on-site visits, each safety and hygiene control practice were differentiated into a poor, basic, intermediate or standard level. Milk samples were collected with a 7-day interval over three-time points to determine total bacterial counts (TBC), coliforms and Staphylococcus aureus. Besides, aflatoxin M1 (AFM1) occurrence was determined in farm milk as an indication of feed storage and monitoring practices. Data showed that none of the chain actors attained the standard level on any of the safety and hygiene control practices. Cluster analysis of on-farm safety and hygiene control practices generated two clusters, which differed mainly on the scores for udder and teat care, and disease detection practices. Differences in safety and hygiene control practices observed among farmers did not translate into differences in milk quality and safety. The analysis for AFM1 showed that 22% exceeded the maximum limit of the United States Food and Drug Authority Standard. Also, the microbial data showed that the farm milk already exceeded maximum limits of the East Africa Community (EAC) standard to the extent that no continued growth was observed further in the chain. The study demonstrates that improvements in milk quality and safety would require multiple practices to be upgraded to the standard level. Research is needed to advance the performance of control practices towards compliance with international standard requirements.

    Fluorescence spectroscopy and chemometrics for simultaneous monitoring of cell concentration, chlorophyll and fatty acids in Nannochloropsis oceanica
    Sá, Marta ; Bertinetto, Carlo G. ; Ferrer-Ledo, Narcís ; Jansen, Jeroen J. ; Wijffels, Rene ; Crespo, João G. ; Barbosa, Maria ; Galinha, Claudia F. - \ 2020
    Scientific Reports 10 (2020)1. - ISSN 2045-2322 - 10 p.

    Online monitoring of algal biotechnological processes still requires development to support economic sustainability. In this work, fluorescence spectroscopy coupled with chemometric modelling is studied to monitor simultaneously several compounds of interest, such as chlorophyll and fatty acids, but also the biomass as a whole (cell concentration). Fluorescence excitation-emission matrices (EEM) were acquired in experiments where different environmental growing parameters were tested, namely light regime, temperature and nitrogen (replete or deplete medium). The prediction models developed have a high R2 for the validation data set for all five parameters monitored, specifically cell concentration (0.66), chlorophyll (0.78), and fatty acid as total (0.78), saturated (0.81) and unsaturated (0.74). Regression coefficient maps of the models show the importance of the pigment region for all outputs studied, and the protein-like fluorescence region for the cell concentration. These results demonstrate for the first time the potential of fluorescence spectroscopy for in vivo and real-time monitoring of these key performance parameters during Nannochloropsis oceanica cultivation.

    A customized assessment tool to differentiate safety and hygiene control practices in emerging dairy chains
    Ledo, James ; Hettinga, Kasper A. ; Luning, Pieternel A. - \ 2020
    Food Control 111 (2020). - ISSN 0956-7135
    Aflatoxins - Dairy chain actors - Dairy farmers - Fresh milk - Hygienic milking - Microbial

    In emerging dairy chains, inconsistent product quality and safety are recurring issues. The need for improvement in hygiene and safety control practices to meet rapidly growing demands for dairy products quality and safety is imperative. However, existing assessment tools do not consider specific situations in emerging dairy chains, where practices are often performed below standard requirements, which presents an inaccurate picture when these tools would be used. This study presents the development of a customized tool to assess and differentiate levels of safety and hygiene control practices in emerging dairy chains. The tool consists of indicators to analyse control practices and four corresponding grids to assess and differentiate the levels of the safety and hygiene control practices at the farm, during transportation, milk collection, and at local retail points crucial for microbial and chemical (i.e. aflatoxin) safety. The customized tool was piloted in Tanzania to assess on-farm practices, as an example of an emerging dairy chain, using interviews, farm visits and audio-visual assisted observations. Thirty-eight small and three large-scale farmers were interviewed, and their control practices observed. The responses were scored based on the grids and the scores were used for data analysis to identify patterns among the farmers. Overall, the customized assessment tool was able to accurately differentiate safety and hygiene practices of the farmers into three distinct clusters. The majority of the small-scale dairy farmers were performing practices at poor to basic level with very few practices at an intermediate level. The large-scale farmers were operating mainly at intermediate to standard level but with basic level performance on milk safety monitoring method, udder and teat care, and personal hygiene practices. Overall, incremental changes are required for on-farm practices to adequately mitigate microbial and aflatoxin contamination of fresh milk. Furthermore, the obtained profiles on farmers safety and hygiene control practices provide input for the development of training programs tailored to the knowledge and skills needs of groups of farmers with similar performance levels. Further research is needed to provide insight into the relationship between the level of control practices and milk safety outcomes.

    Monitoring of eicosapentaenoic acid (EPA) production in the microalgae Nannochloropsis oceanica
    Sá, Marta ; Ferrer-Ledo, Narcís ; Wijffels, Rene ; Crespo, João G. ; Barbosa, Maria ; Galinha, Claudia F. - \ 2020
    Algal Research 45 (2020). - ISSN 2211-9264
    Chemometric modelling - Eicosapentaenoic acid (EPA) - Fluorescence spectroscopy - Nannochloropsis oceanica - Omega-3 fatty acid

    With the increase awareness for a healthier food regime and greener environmental processes, microalgae are being looked as a solution for a sustainable production of polyunsaturated fatty acids, such as omega-3 eicosapentaenoic acid (EPA). Nannochloropsis oceanica is an oleaginous microalga, well-known for the ability of EPA accumulation, although higher lipid productivities are still required to make the process competitive. Therefore, three cultivation parameters were tested in the present work (temperature, light cycles and nitrogen supply) in order to study the EPA profile in the polar and neutral fractions of the cells. In addition, an online monitoring tool based on a fluorescence spectroscopy technique was developed with the aim of increasing process knowledge at real time. The results of this work show that nitrogen depletion induces the highest variability in EPA accumulation in the neutral fraction (triacylglycerols). However, to increase the EPA content in the polar fraction a different strategy needs to be implemented, such as decreasing the cultivation temperature or the light available per cell. Chemometric models were developed through PCA (Principal Component Analysis) and PLS (Projection to Latent Structures), using only fluorescence spectra as inputs, enabling the monitoring of EPA in both fractions separately. High explained variance was observed (above 85%) in both fractions, with R2 above 0.81 and slopes above 0.93 for both validation and training data sets. Lower values of cross-validation and prediction errors were observed (between 0.29 and 0.49% g/gDW). The results obtained show that fluorescence spectroscopy is a powerful technique for online monitoring of non-fluorophore molecules, such as EPA, in complex process like microalgae cultivation.

    Persistent challenges in safety and hygiene control practices in emerging dairy chains: The case of Tanzania
    Ledo, James ; Hettinga, Kasper A. ; Bijman, Jos ; Luning, Pieternel A. - \ 2019
    Food Control 105 (2019). - ISSN 0956-7135 - p. 164 - 173.
    Dairy system - Formal dairy chain - Informal dairy chain - Milk safety - On-farm practices - Support programs

    In emerging economies, the demand for milk and milk products is growing speedily, leading to rapidly evolving dairy chains. However, milk quality and safety are not yet up to standard, despite substantial efforts to support actors in these emerging dairy chains. The aim of this study was therefore to get insight in possible causes of persisting poor milk safety and hygiene practices. The Tanzanian dairy chain was taken as a case for an emerging dairy chain, because of its evolving nature and potential for growth. Depicting the organization of the dairy system involved a value chain analysis using focus group discussions and interviews with chain actors (in total 71). Face-to-face in-depth interviews and systematic on-site observations at actor locations in two different regions provided insights into current safety and hygiene control practices from the farm to the processor. Furthermore, 22 farmers were interviewed to examine how they perceived existing support programs in assisting their safety and hygiene practices. Data showed that the organization of control activities and enforcement of requirements on dairy quality is not uniform across the dairy chain. Overall, safety and hygiene practices were basic or rudimentary. Preventive practices related to animal health care, hygiene, and feed storage control, were mostly lacking. Milk cooling is not a common practice along the dairy chain, monitoring of milk safety and quality parameters is limited, particularly for pathogenic bacteria, indicating a risk for milk safety. Farmers perceived the support of the non-commercial program as more supportive to their on-farm safety and hygiene control practices than the commercial program. To avert public health risks of the increasing milk consumption, multiple safety and hygiene control practices require significant improvement. Support programs could more explicitly enhance awareness and competences on these safety and hygiene practices.

    Strain improvement of Nannochloropsis oceanica for the production of polyunsaturated fatty acids
    Ferrer Ledo, N. - \ 2018
    Strain improvement of microalgae for the production of omega-3 fatty acids
    Ferrer Ledo, N. - \ 2018
    Metabolic modelling and energy parameter estimation of Tetradesmus obliquus
    León-Saiki, G.M. ; Ferrer Ledo, Narcís ; Lao-Martil, David ; Veen, Douwe van der; Wijffels, René H. ; Martens, Dirk E. - \ 2018
    Algal Research 35 (2018). - ISSN 2211-9264 - p. 378 - 387.
    Compartmentalized metabolism - Flux Balance Analysis (FBA) - Maintenance requirement - Microalgae - Scenedesmus obliquus

    We developed a metabolic network describing the primary metabolism of Tetradesmus obliquus aimed to get a better understanding of metabolism to improve industrial production. The network includes 351 reactions with 183 metabolites distributed over 4 compartments: cytosol, chloroplast, mitochondria, and extracellular space. The energy requirements for biomass assembly and maintenance (Kx and mATP, respectively) were experimentally determined from batch cultures and included in the model. The determined values were 121.02 mmolATP·gDW −1 for Kx and 0.66 mmolATP·gDW −1·h−1 for the mATP. The maintenance value found for T. obliquus is, to our knowledge, one of the lowest reported in literature for microalgae. This low value is also in agreement with the photon maintenance requirement found experimentally for T. obliquus (1.18 mmolph·gDW −1·h−1). Finally, the theoretical maximum yields based on the model for biomass, triacylglycerides (TAG), and starch yield on light were calculated to be 1.15 g·molph −1, 1.05 gTAG·molph −1, and 2.69 gstarch·molph −1.

    Tropical forest canopies and their relationships with climate and disturbance: results from a global dataset of consistent field-based measurements
    Pfeifer, Marion ; Gonsamo, Alemu ; Woodgate, William ; Cayuela, Luis ; Marshall, Andrew R. ; Ledo, Alicia ; Paine, Timothy C.E. ; Marchant, Rob ; Burt, Andrew ; Calders, Kim ; Courtney-mustaphi, Colin ; Cuni-sanchez, Aida ; Deere, Nicolas J. ; Denu, Dereje ; Gonzalez De Tanago Meñaca, J. ; Hayward, Robin ; Lau Sarmiento, A.I. ; Macía, Manuel J. ; Olivier, Pieter I. ; Pellikka, Petri ; Seki, Hamidu ; Shirima, Deo ; Trevithick, Rebecca ; Wedeux, Beatrice ; Wheeler, Charlotte ; Munishi, Pantaleo K.T. ; Martin, Thomas ; Mustari, Abdul ; Platts, Philip J. - \ 2018
    Forest Ecosystems 5 (2018). - ISSN 2095-6355 - 14 p.
    Background: Canopy structure, defined by leaf area index (LAI), fractional vegetation cover (FCover) and fraction of absorbed photosynthetically active radiation (fAPAR), regulates a wide range of forest functions and ecosystem services. Spatially consistent field-measurements of canopy structure are however lacking, particularly for the tropics. Methods: Here, we introduce the Global LAI database: a global dataset of field-based canopy structure measurements spanning tropical forests in four continents (Africa, Asia, Australia and the Americas). We use these measurements to test for climate dependencies within and across continents, and to test for the potential of anthropogenic disturbance and forest protection to modulate those dependences. Results: Using data collected from 887 tropical forest plots, we show that maximum water deficit, defined across the most arid months of the year, is an important predictor of canopy structure, with all three canopy attributes declining significantly with increasing water deficit. Canopy attributes also increase with minimum temperature, and with the protection of forests according to both active (within protected areas) and passive measures (through topography). Once protection and continent effects are accounted for, other anthropogenic measures (e.g. human population) do not improve the model. Conclusions: We conclude that canopy structure in the tropics is primarily a consequence of forest adaptation to the maximum water deficits historically experienced within a given region. Climate change, and in particular changes in drought regimes may thus affect forest structure and function, but forest protection may offer some resilience against this effect.
    Strain improvement of microalgae for the production of omega-3 fatty acids
    Ferrer Ledo, N. - \ 2017
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