A.J.B. van Boxtel

Wageningen University, Wageningen, Gelderland, Netherlands

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Publications (46)68.46 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: This work concerns the degradation of the nutritional compounds glucoraphanin (GR) and vitamin C (Vc), and the inactivation of the enzyme myrosinase (MYR) in broccoli (Brassica oleracea var. italica) during drying with air temperatures in the range of 30–60 °C. Dynamic optimization is applied to find the optimized temperature trajectories that minimize degradation and inactivation. Simulation and experimental results for optimized temperature trajectories are compared to constant inlet air temperature drying at 40 and 50 °C. The results show that with the optimized temperature trajectories the retention of GR, MYR and Vc improved significantly. Moreover, the experiments show that degradation and inactivation during drying is slower than expected from kinetic studies. The deviation is explained from the difference in the physical state of the samples used in the drying experiments, i.e. original plant tissue versus the grounded state of the plant tissue used in the experiments for the kinetic studies. The results indicate that besides temperature and moisture content the physical state is also an important aspect in the degradation of nutritional compounds and enzymes.
    LWT - Food Science and Technology. 11/2014; 59(1):189–195.
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    ABSTRACT: The analyses of algae biorefinery performance are commonly based on fixed performance data for each processing step. In this work, we demonstrate a model-based combinatorial approach to derive the design-specific upstream energy consumption and biodiesel yield in the production of biodiesel from microalgae. Process models based on mass and energy balances and conversion relationships are presented for several possible process units in the algae processing train. They allow incorporating the effects of throughput capacity and process conditions, which is not possible in the data-based approach. Therefore, the effect of choices in the design on the overall performance can be quantified. The process models are organised in a superstructure to evaluate all combinations of routings. First, this is done for selected fixed design conditions, which is followed by optimisation of the process conditions for each route by maximising the net energy ratio (NER), based on upstream energy consumption and biodiesel yield. A scenario based on current energy production and state-of-the art techniques for algae processing is considered. The optimised process conditions yield NER values which are up to about 30% higher than those for fixed process conditions. In addition, the approach allows a quantitative bottleneck analysis for each process route. The model-based approach proves to be a versatile tool to guide the design of efficient microalgae processing systems.
    Algal Research. 07/2014; 5:140–157.
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    ABSTRACT: In this work, the Flory Huggins Free Volume theory is used to interpret the sorption isotherms of broccoli from its composition and using physical properties of the components. This theory considers the mixing properties of water, biopolymers and solutes and has the potential to describe the sorption isotherms for varying product moisture content, composition and temperature. The required physical properties of the pure components in food became available in recent years and allow now the prediction of the sorption isotherms with this theory. Sorption isotherm experiments have been performed for broccoli florets and stalks, at two temperatures. Experimental data shows that the Flory Huggins Free Volume (FHFV) theory represents the sorption isotherm of fresh and blanched broccoli samples accurately. The results also show that blanching affects the sorption isotherm due to the change of composition via leaching solutes and the change of interaction parameter due to protein denaturation.
    Food Biophysics 01/2014; 9(1). · 1.64 Impact Factor
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    ABSTRACT: To evaluate microalgae production in large scale open ponds under different climatologic conditions, a model-based framework is used to study the effect of light conditions, water temperature and reactor design on trends in algae productivity. Scenario analyses have been done for two algae species using measured weather data of the Netherlands and Algeria. The effects of temperature control, photo-inhibition and using monthly or yearly fixed biomass concentrations are estimated by a sensitivity analysis. The calculation-based results show that climate conditions such as solar irradiation and temperature dynamics play an important role in open raceway ponds. In moderate climate zones low and high temperatures over a season suppress growth. At high latitudes this effect is important as light levels vary much during the day and between seasons. Optimal biomass concentrations in ponds depend on location, pond depth and algae species. Pond design, location and algae species interact and productivity cannot be based solely on general or assumed efficiencies. It is essential to select algae species that have a suitable growth rate, light absorption coefficient and the ability to grow over a broad temperature range. The presented approach gives a framework to validate specific cultivation systems.
    Algal Research. 10/2013;
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    ABSTRACT: Microalgae productivity in tubular photobioreactors depends on algae species, location, tube diameter, biomass concentration, distance between tubes and for vertically stacked systems, the number of horizontal tubes per stack. A simulation model for horizontal and vertically stacked horizontal tubular reactors was made to quantify the effect of these decision variables on production yield. The model uses reactor dimensions, dynamic sunlight patterns over the day and year, and growth characteristics of algae species as inputs. Scenario studies were done to study the effect of decision variables on reactor performance in The Netherlands, France and Algeria. Results indicate that the areal biomass productivity in vertically stacked photobioreactors is 25–70% higher than in plain horizontal systems. Reactor design is location specific because light conditions differ. In The Netherlands, the best horizontal distance between tubes is 0.05 m for horizontal and 0.25 m for vertical systems. For France and Algeria, the best horizontal distance between vertical systems is 0.20 m and 0.15 m respectively. System performance can be improved further by using light reflection materials on the ground surface. Improving the transparency properties of tube material does not significantly affect areal productivity.
    Applied Energy. 01/2013; 105:395-406.
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    ABSTRACT: This work presents an approach to compute dryer energy efficiency using air flowrate step responses and establish a link between drying energy efficiency and process controllability. The approach is based on the temperature drop between the dryer inlet and outlet air under adiabatic conditions and so decouples water evaporation from heat loss and product heating effects on dryer temperature drop. As such, the computation is accurate even for dryers with significant heat losses where the traditional use of actual temperature drop measurements is grossly inaccurate. The approach is tested and verified on two experimental case studies involving significant heat losses: the first, a continuous fluidized-bed dryer (from literature); the second, a conventional and zeolite wheel-assisted batch dryer designed in the current study.
    Drying Technology 01/2013; 31(16). · 1.81 Impact Factor
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    ABSTRACT: Cells react to various forms of physical phenomena that promote and maintain the formation of tissues. The best example of this are cells of musculoskeletal origin, such as mesenchymal stem cells (MSCs), which consistently proliferate or differentiate under cues from hydrostatic pressure, diffusive mass transport, shear stress, surface chemistry, mechanotransduction, and molecular kinetics. To date, no other cell type shows greater receptiveness to macroscopic and microscopic cues, highlighting the acute sensitivity of MSCs and the importance of physical principles in tissue homeostasis. In this review, we describe the literature that has shown how physical phenomena govern MSCs biology and provide insight into the mechanisms and strategies that can spur new biotechnological applications with tissue biology.
    Trends in Biotechnology 09/2012; 30(11):583-90. · 9.66 Impact Factor
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    ABSTRACT: One of the challenges in genetic network reconstruction is finding experimental designs that maximize the information content in a data set. In this work, the information value of mRNA transcription time course experiments was used to compare experimental designs. The study concerns the dynamic response of genes in the XlnR regulon of Aspergillus niger, with the goal to find the best moment in time to administer an extra pulse of inducing D-xylose. Low and high D-xylose pulses were used to perturb the XlnR regulon. Evaluation of the experimental methods was based on simulation of the regulon. Models that govern the regulation of the target genes in this regulon were used for the simulations. Parameter sensitivity analysis, the Fisher Information Matrix (FIM) and the E-modified criterion were used to assess the design performances. The results show that the best time to give a second D-xylose pulse is when the D-xylose concentration from the first pulse has not yet completely faded away. Due to the presence of a repression effect the strength of the second pulse must be optimized, rather than maximized. The results suggest that the modified E-criterion is a better metric than the sum of integrals of absolute sensitivity for comparing alternative designs.
    IEEE/ACM transactions on computational biology and bioinformatics / IEEE, ACM 04/2012; · 2.25 Impact Factor
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    ABSTRACT: Aspergillus niger is an important organism for the production of industrial enzymes such as hemicellulases and pectinases. The xylan-backbone monomer, d-xylose, is an inducing substance for the coordinate expression of a large number of polysaccharide-degrading enzymes. In this study, the responses of 22 genes to low (1 mM) and high (50 mM) d-xylose concentrations were investigated. These 22 genes encode enzymes that function as xylan backbone-degrading enzymes, accessory enzymes, cellulose-degrading enzymes, or enzymes involved in the pentose catabolic pathway in A. niger. Notably, genes encoding enzymes that have a similar function (e.g., xylan backbone degradation) respond in a similar manner to different concentrations of d-xylose. Although low d-xylose concentrations provoke the greatest change in transcript levels, in particular, for hemicellulase-encoding genes, transcript formation in the presence of high concentrations of d-xylose was also observed. Interestingly, a high d-xylose concentration is favorable for certain groups of genes. Furthermore, the repressing influence of CreA on the transcription and transcript levels of a subset of these genes was observed regardless of whether a low or high concentration of d-xylose was used. Interestingly, the decrease in transcript levels of certain genes on high d-xylose concentrations is not reflected by the transcript level of their activator, XlnR. Regardless of the d-xylose concentration applied and whether CreA was functional, xlnR was constitutively expressed at a low level.
    Applied and Environmental Microbiology 02/2012; 78(9):3145-55. · 3.95 Impact Factor
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    ABSTRACT: This work presents a mixed integer nonlinear programming (MINLP) formulation for the design of energy-efficient multistage adsorption dryers within constraints on product temperature and moisture content. Apart from optimizing temperatures and flows, the aim is to select the most efficient adsorbent per stage and product to air flow configuration. Superstructure models consisting of commonly used adsorbents such as zeolite, alumina, and silica-gel are developed and optimized for a two-stage, low-temperature, adsorption drying system. Results show that the optimal configuration is a hybrid system with zeolite as the first-stage adsorbent and silica-gel as the second-stage adsorbent in counter-current flow between drying air and product. A specific energy consumption of 2,275 kJ/kg is achieved, which reduces to 1,730 kJ/kg with heat recovery by a heat exchanger. Compared to a conventional two-stage dryer at the same drying temperature, this represents a 59% reduction in energy consumption. The optimal system ensures the exhaust air temperature of the first-stage regenerator is high enough to regenerate the second-stage adsorbent so no utility energy is spent in the second stage. A higher second-stage adsorbent wheel speed favors energy performance as it becomes optimized for energy recovery while the first is optimized for dehumidification. Although this work considers three candidate adsorbents in a two-stage system, the same reasoning can be applied to systems with more stages and adsorbents. The developed superstructure optimization methodology can, by extension, be applied to optimize multistage hybrid drying systems in general for any objective.
    Drying Technology - DRY TECHNOL. 01/2012; 30(8):873-883.
  • X. Jin, R. G. M. van der Sman, A. J. B. van Boxtel
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    ABSTRACT: Moisture diffusion in porous broccoli florets and stalks is modeled using the free volume and Maxwell-Eucken theories. These theories are based on the mobility of water and concern the variation of the effective diffusion coefficient for a wide range of temperature and moisture content during product drying. Mass and heat transport, shrinkage, and vitamin C degradation during drying of broccoli are simulated by a spatial model. The effective diffusion coefficient varies strongly with product moisture content and temperature. Vitamin C degradation is high at moisture contents around 2 kg water/kg dry matter. The influence of the size of broccoli on the drying rate is evaluated for several types of broccoli florets and stalks.
    Drying Technology 12/2011; 29(16):1963-1971. · 1.81 Impact Factor
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    ABSTRACT: Low-temperature drying is important for heat-sensitive products, but at these temperatures conventional convective dryers have low energy efficiencies. To overcome this challenge, an energy efficiency optimization procedure is applied to a zeolite adsorption dryer subject to product quality. The procedure finds a trade-off between the improved drying capacity due to dehumidification and energy expenditure due to regeneration while incorporating product drying properties. By optimizing the regeneration air inlet temperature, drying air, adsorbent, and regeneration air flow rates as well as sensible and latent heat recovery from the regenerator exhausts, the energy efficiency is improved by up to 45 % compared to the state-of-the-art. The high mass transfer effect of high temperatures is utilized in the regenerator to boost dehumidification while isolating the heat-sensitive dried product from the quality-degrading effect.
    Chemical Engineering & Technology 09/2011; 34(10):1723 - 1732. · 1.37 Impact Factor
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    ABSTRACT: The nutritional requirements of stem cells have not been determined; in particular, the amino acid metabolism of stem cells is largely unknown. In this study, we investigated the amino acid metabolism of human mesenchymal stem cells (hMSCs), with focus on two questions: Which amino acids are consumed and/or secreted by hMSCs and at what rates? To answer these questions, hMSCs were cultured on tissue culture plastic and in a bioreactor, and their amino acid profile was analyzed. The results showed that the kinetics of hMSCs growth and amino acid metabolism were significantly higher for hMSCs in tissue culture plastic than in the bioreactor. Despite differences in culture conditions, 8 essential and 6 nonessential amino acids were consumed by hMSCs in both tissue culture plastic and bioreactor cultures. Glutamine was the most consumed amino acid with significantly higher rates than for any other amino acid. The metabolism of nonessential amino acids by hMSCs deviated significantly from that of other cell lines. The secretion of alanine, glycine, glutamate, and ornithine by hMSCs showed that there is a strong overflow metabolism that can be due to the high concentrations of amino acids provided in the medium. In addition, the data showed that there is a metabolic pattern for proliferating hMSCs, which can contribute to the design of medium without animal serum for stem cells. Further, this study shows how to implement amino acid rates and metabolic principles in three-dimensional stem cell biology.
    Tissue Engineering Part A 09/2011; 18(5-6):654-64. · 4.64 Impact Factor
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    ABSTRACT: Conventionally, energy-saving techniques in drying technology are sequential in nature. First, the dryer is optimized without heat recovery and then, based on the obtained process conditions, heat recovery possibilities are explored. This work presents a methodology for energy-efficient adsorption dryer design that considers sensible and latent heat recovery as an integral part of drying system design. A one-step pinch-based optimization problem is formulated to determine the operating conditions for optimal energy performance of such an integrated system subject to product quality. Because the inlet and target stream properties of the heat recovery network are determined by the adsorption drying conditions, they are unknown a priori and thus are determined simultaneously within the overall optimization using the pinch location method. Energy balances are written above and below the various pinch point possibilities and the optimal pinch point is that which minimizes the amount of external heating utility required while satisfying drying and thermodynamic constraints. Results for a single-stage zeolite adsorption drying process with simultaneous heat recovery optimization show a 15% improvement in efficiency compared to a sequentially optimized system. The improvement is traceable to alterations in enthalpy-related variables like temperatures and flow rates. The discrepancy in optimal operating conditions between the sequential and simultaneous cases underscores the need to change system operating conditions when retrofitting for heat recovery because previous optimal conditions become suboptimal when heat recovery is introduced. Also, compared to a conventional dryer (without an adsorption process) operating under similar conditions, energy consumption is reduced by about 55%.
    Drying Technology 09/2011; 29(12):1459-1471. · 1.81 Impact Factor
  • Computational Methods in Systems Biology, 9th International Conference, CMSB 2011, Paris, France, September 21-23, 2011. Proceedings; 01/2011
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    ABSTRACT: The internal moisture distribution that arise in food products during drying, is a key factor for the retention of quality attributes. To reveal the course of moisture content in a product, internal moisture profiles in broccoli florets are measured by MRI imaging during drying experiments with controlled air flow and temperature. The 3D images concern a matrix size of 64×64×64 elements. Signal intensity is converted to product moisture content with a linear relationship, while taking a minimum detectable moisture content of 0.3 kg water/ kg dry matter into account. Moisture content as a function of time is presented for a 2D cross sectional area in the middle of a broccoli sample.The average moisture contents for the cross sectional area obtained from the MRI imaging are compared with spatial model simulations for the moisture distribution. In that model the effective diffusion coefficient is based on the Free Volume Theory. This theory has the advantage that the changed mobility of water in the product during drying is taken into account and the theory also predicts the moisture transport in the porous broccoli floret. Key parameters for the Free Volume Theory are estimated by fitting to the experimental MRI results and the effective diffusion coefficient is given as a function of the product water content.
    Procedia Food Science. 01/2011; 1:640-646.
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    ABSTRACT: The effect of drying conditions on the color of tarragon (Artemisia dracunculus L.) leaves was studied. Tarragon leaves were dried at temperatures of 40 to 90°C with a constant airflow of 0.6m/s. The samples were collected at 7%, 10%, 20%, and 30% moisture content wet basis for evaluation of the color change. The color parameters of fresh and dried leaves were measured by a colorimeter. The individual parameters of L*a*b* and L*C*h° color systems were evaluated and h° proved to be the best parameter to monitor color change. The smallest change of the color parameters was observed at 40°C, in which temperature was low, and also at 90°C, when drying time was short. The biggest change occurred at the temperatures of 50 to 70°C. Most of the color change happened before the material reaches 35% moisture content. The combination of drying time and temperature defines the change of color. Keywords Artemisia dracunculus –Color–Drying–French Tarragon–Russian Tarragon
    Food and Bioprocess Technology 01/2011; 4(7):1281-1287. · 4.12 Impact Factor
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    ABSTRACT: In this paper the dynamics of the transcription-translation system for XlnR regulon in Aspergillus niger is modeled. The model is based on Hill regulation functions and uses ordinary differential equations. The network response to a trigger of D-xylose is considered and stability analysis is performed. The activating, repressive feedback, and the combined effect of the two feedbacks on the network behavior are analyzed. Simulation and systems analysis showed significant influence of activating and repressing feedback on metabolite expression profiles. The dynamics of the D-xylose input function has an important effect on the profiles of the individual metabolite concentrations. Variation of the time delay in the feedback loop has no significant effect on the pattern of the response. The stability and existence of oscillatory behavior depends on which proteins are involved in the feedback loop. The dynamics in the regulation properties of the network are dictated mainly by the transcription and translation degradation rate parameters, and by the D-xylose consumption profile. This holds true with and without feedback in the network. Feedback was found to significantly influence the expression dynamics of genes and proteins. Feedback increases the metabolite abundance, changes the steady state values, alters the time trajectories and affects the response oscillatory behavior and stability conditions. The modeling approach provides insight into network behavioral dynamics particularly for small-sized networks. The analysis of the network dynamics has provided useful information for experimental design for future in vitro experimental work.
    BMC Systems Biology 01/2011; 5 Suppl 1:S14. · 2.98 Impact Factor
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    ABSTRACT: Evaluation of the potential of algae production for biofuel and other products at various locations throughout the world requires assessment of algae productivity under varying light conditions and different reactor layouts. A model was developed to predict algae biomass production in flat panel photobioreactors using the interaction between light and algae growth for the algae species Phaeodactylum tricornutum and Thalassiosira pseudonana. The effect of location, variable sunlight and reactor layout on biomass production in single standing and parallel positioned flat panels was considered. Three latitudes were studied representing the Netherlands, France and Algeria. In single standing reactors the highest yearly biomass production is achieved in Algeria. During the year biomass production fluctuates the most in the Netherlands, while it is almost constant in Algeria. Several combinations of path lengths and biomass concentrations can result in the same optimal biomass production. The productivity in parallel place flat panels is strongly influenced by shading and diffuse light penetration between the panels. Panel orientation has a large effect on productivity and at higher latitudes the difference between north–south and east–west orientation may go up to 50%.
    Applied Energy - APPL ENERG. 01/2011; 88(10):3342-3353.

Publication Stats

215 Citations
68.46 Total Impact Points

Institutions

  • 1997–2014
    • Wageningen University
      • • Division of Biomass Refinery and Process Dynamics
      • • Laboratory of Systems and Synthetic Biology
      • • Cluster of Food Sciences
      Wageningen, Gelderland, Netherlands
  • 1999
    • Tea Research Foundation of Central Africa
      Mashaba, Masvingo, Zimbabwe