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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    Selective separation of flavour-active compounds from strip gas using frictional diffusion
    Ammari, Ali ; Schroën, Karin G.P.H. ; Boom, Remko M. - \ 2020
    Separation and Purification Technology 251 (2020). - ISSN 1383-5866
    Beer - Flavour separation - Frictional diffusion - Gas-phase

    Attaining constant flavour composition in products that are produced batch-wise, such as beer, is not trivial given the inherent variability in fermentation. CO2 stripping is feasible but unselective. Condensation of the flavour is possible but energy intensive. We here propose the use of frictional diffusion (also called FricDiff), which is based on differences in diffusion rates in a sweep or carrier gas such as CO2 through an inert porous medium. Application of a slight counter-flow of the sweep gas can be used to adapt the selectivity between different flavours. It is shown that from a difference in diffusion rate of 25%, a selectivity of more than 10 can be obtained between ethyl acetate and isoamyl acetate, albeit at the cost of the flavour flux through the porous barrier.

    Modelling temperature effects in a membrane cascade system for oligosaccharides
    Rizki, Zulhaj ; Suryawirawan, Eric ; Janssen, Anja E.M. ; Padt, Albert van der; Boom, Remko M. - \ 2020
    Journal of Membrane Science 610 (2020). - ISSN 0376-7388
    Membrane cascades - Modelling - Nanofiltration - Oligosaccharide fractionation - Temperature effect

    Open nanofiltration of mixtures of fructo-oligosaccharides was assessed by experiment and by modelling the overall permeation behaviour of 3 different membranes. The temperature effect was modelled using the steric pore model, incorporating the molecular volumetric expansion of fructo-oligosaccharides as solutes, the decrease in the solution viscosity and the volumetric expansion of the membrane with increasing temperature. The thermal expansion of the solute was described as a linear increase in the bare molecular volume plus a non-linear decrease in its hydration number. The viscosity reduction was modelled by incorporating the temperature as a variable into an existing exponential relation derived by Chirife and Buera. The thermal expansion of membranes was described with a linear increase in the pore size and a linear decrease in its hydrodynamic resistance. Although the purity of the oligosaccharide product was hardly affected by the temperature, the yield was much lower at higher temperatures. The yield can therefore be improved by decreasing the temperature while maintaining the product purity. This behaviour was also observed in a 3-stage filtration cascade. The temperature effect is closely related to the increase in fluxes with temperature, leading to a different split of the feed into permeate and retentate. In a membrane cascade, the lower yield with higher temperatures was seen most strongly at the top stage, and much less at the middle and lower stages, which can be explained by the configuration of the cascade.

    Steering protein and salt ad- and desorption by an electrical switch applied to polymer-coated electrodes
    Fritz, P.A. ; Zhang, P. ; Bruschinski, Tom ; Sahin, S. ; Smet, L.C.P.M. de; Chan-Park, M.B. ; Boom, R.M. ; Schroën, C.G.P.H. - \ 2020
    Separation and Purification Technology 250 (2020). - ISSN 1383-5866
    Although solid-phase chromatography is a well-established method for protein separation, chemically intensive and often costly regeneration steps are needed to make reuse of the adsorbent possible. Here, we demonstrate the use of electrochemical principles as sustainable alternative. We make use of spontaneous adsorption of proteins to solid electrodes and reverse this process by applying an electric potential to regenerate the interface. This allows for adsorption of proteins to take place at 0 V difference between the electrodes, due to electrostatic interactions between the protein and the electrode surface. The desorption is then triggered by applying a potential difference (−1.2 V) between the electrodes.

    It is demonstrated that the incorporation of negatively charged polystyrene sulfonate (PSS) or positively charged polydiallyldimethylammonium chloride (PDMAC) in or on top of the respective activated carbon electrodes increases the amount of exchanged protein from 1 to 10 mg g−1, as compared to simple activated carbon electrodes. Interestingly, salt ad- and desorption occurs in opposite cycles compared to protein ad- and desorption, resulting in simultaneous concentration and desalting of the protein when 0 V is applied. On top of that, we also found that an enrichment in β-lactoglobulin could be achieved starting from whey protein isolate. These results clearly demonstrate that electrochemical technologies can be used not only for protein separation (including removal of salt), but also for protein fractionation, while not requiring solvent use.
    Influence of soaking time on the mechanical properties of rapeseed and their effect on oleosome extraction
    Romero-Guzmán, María Juliana ; Vardaka, Eirini ; Boom, Remko M. ; Nikiforidis, Constantinos V. - \ 2020
    Food and Bioproducts Processing 121 (2020). - ISSN 0960-3085 - p. 230 - 237.
    Aqueous extraction - Oil bodies - Oleosomes - Rapeseed - Rapeseed microstructure - Soaking time - Twin-screw press

    Oleosomes (or oil-bodies) are the oil storage structures of plant seeds. We typically extract oil by disrupting the oleosomes through mechanical-pressing of dry seeds and by using organic solvents. Nevertheless, it is possible to extract whole oleosomes, by breaking pre-soaked seeds. A key point to avoid oleosome damage seems to be the soaking step. Hence the aim of this work was to understand the effect of soaking time on the mechanical properties of rapeseed and its effect on oleosome extraction. The results showed that the diffusion of water through the seeds was negatively associated to the mechanical strength of the seeds. This effect occurs in 3 stages and reaches a plateau at 8 h. The extraction of oleosomes and proteins kept constant for all different treatments. However, the duration of the soaking step influences oleosome integrity, as oleosomes extracted after shorter soaking times (<8 h) yielded bigger oleosomes with extraneous proteins bounded to them. After 8 h soaking time, the mechanical properties of the seeds kept constant and oleosomes of native size and with oleosome endogenous proteins were recovered. Therefore, a minimum soaking time of 8 h is required to achieve the extraction of intact oleosomes.

    Solute inclusion and freezing rate during progressive freeze concentration of sucrose and maltodextrin solutions
    Vuist, Jan Eise ; Boom, Remko M. ; Schutyser, Maarten A.I. - \ 2020
    Drying Technology (2020). - ISSN 0737-3937
    Freeze concentration - solute inclusion - sucrose

    Progressive freeze concentration is an alternative method to concentrate aqueous industrial streams compared to evaporation or membrane separation. In this research sucrose and maltodextrin solutions were concentrated in a stirred progressive freeze concentrator. The solute inclusion in the formed ice was studied using varying stirring speeds, initial concentrations and freezing plate temperatures. Under constant freezing plate temperature, a lower limit was found for the solute inclusions with increasing stirrer speeds. To improve the freeze concentration process, a decreasing temperature ramp was applied to the freezing plate. This yielded 2 to 3 times less solute inclusions in the ice, while maintaining similar ice yields.

    Controlled oleosome extraction to produce a plant-based mayonnaise-like emulsion using solely rapeseed seeds
    Romero-Guzmán, María Juliana ; Köllmann, Nienke ; Zhang, Lu ; Boom, Remko M. ; Nikiforidis, Constantinos V. - \ 2020
    Food Science and Technology = Lebensmittel-Wissenschaft und Technologie 123 (2020). - ISSN 0023-6438
    Emulsion - Mayonnaise - Novel-ingredients - Oil-bodies - Oleosomes - Plant-based

    Oleosomes are oil storage structures in seeds, consisting of triglycerides surrounded by a protein-phospholipid mixed monolayer. They can be extracted aqueously together with other seed components such as proteins and soluble fibers. The co-extracted biomolecules can affect the properties of the extracts. Nevertheless, it is possible to control the electrostatic and hydrophobic interactions between these biomolecules and oleosomes by adjusting the extraction conditions. Hence, our aim was to adjust the extraction conditions in order to recover a natural emulsion with a specific functionality: a plant-based mayonnaise-like product, derived solely from rapeseed seeds. By varying the pH of extraction, the droplet size was customized and by increasing the number of purification steps, the right amount of co-extracted material was removed. A combination of these conditions shifted the rheological properties of the obtained natural emulsion to a range similar to the benchmark mayonnaises. This work shows that it is feasible to produce a plant-based mayonnaise with an oil content ranging from 61.7 g/100g to 72.0 g/100g through a simple and continuous oleosome extraction process by controlling the interactions between oleosomes and co-extracted material.

    Efficient single-step rapeseed oleosome extraction using twin-screw press
    Romero-Guzmán, M.J. ; Jung, L. ; Kyriakopoulou, K. ; Boom, R.M. ; Nikiforidis, C.V. - \ 2020
    Journal of Food Engineering 276 (2020). - ISSN 0260-8774
    Aqueous extraction - Natural emulsion - Oil-bodies - Oleosomes - Twin-screw press

    Oil in seeds is encapsulated in oleosomes, which are small lipid droplets surrounded by a phospholipid-protein monolayer. The currently proposed method to extract intact oleosomes includes mixing seeds with alkaline media in a ratio 1:7, batch blending and filtering. In this work, we propose the use of a twin-screw press to perform the oleosome extraction at pH 7. The results show that similarly to blender extraction, twin-screw press recovers ⁓60% of the oleosomes; however the twin-screw press is able to achieve this yield even when just pure water is used. While in the blender extraction, the yield depends on ionic strength and pH of the extraction media, when using twin-screw press, the oleosome extraction yield predominantly depends on the mechanical forces. These shear forces are able to break the cell walls and release the cellular material while maintaining the integrity of oleosomes. The oleosomes extracted with twin-screw press have similar characteristics than those obtained by the blending process. Overall, twin-screw press seems a promising alternative to scale-up the oleosome aqueous extraction, especially as neutral pH can be used and the water usage is significantly reduced. Additionally, preliminary results showed that the yield can increase up to 90 wt%.

    Particle morphology and powder properties during spray drying of maltodextrin and whey protein mixtures
    Both, E.M. ; Boom, R.M. ; Schutyser, M.A.I. - \ 2020
    Powder Technology 363 (2020). - ISSN 0032-5910 - p. 519 - 524.
    Density - Droplet size - Morphology - Pilot scale - Single droplet drying

    Application behavior of spray dried powders such as reconstitution behavior and flowability is indirectly influenced by powder particle morphology. We here investigated the influence of the drying conditions and composition for whey protein (WP), maltodextrin (MD) and their mixtures on particle morphology during pilot-scale spray drying. Even though all powders showed a variety of morphologies, MD powders contained more wrinkled particles and had high bulk density, whereas pure WP powders contained more hollow particles. Mixture powders (75:25 WP:MD) show more hollow particles with increasing inlet temperature, with a lower bulk density. The observed morphologies for different formulations corresponded roughly to previous observations during sessile single droplet drying, but the results indicate that the morphology is also influenced by the faster pilot-scale drying, which was not evident in the slower single droplet drying.

    Dextrose equivalence of maltodextrins determines particle morphology development during single sessile droplet drying
    Siemons, I. ; Politiek, R.G.A. ; Boom, R.M. ; Sman, R.G.M. van der; Schutyser, M.A.I. - \ 2020
    Food Research International 131 (2020). - ISSN 0963-9969
    Glass transition - Maltodextrins - Morphology - Rheology - Single droplet drying

    Particle morphology development during spray drying is critical to powder properties. The aim of this study was to investigate whether the dextrose equivalence (DE) of maltodextrins can be used as an indicator for the final particle morphology. Maltodextrins were characterized on glass transition temperature (Tg) and viscosity, where low DE-value maltodextrins exhibited higher Tg and viscosity than high DE maltodextrins (≥21). A new custom-built sessile single droplet dryer was used to analyse morphology development of minute maltodextrin droplets (R0 ~ 100 μm) at 60 °C and 90 °C. Droplets with low DE showed early skin formation (2–5 s) and developed smoothly shaped particles with large cavities. Rheology on low DE maltodextrin films at dry matter of 82% (w/w) suggested that drying droplets acquired elasticity after locking providing resistance against surface compression. After locking morphology development is probably halted as the glassy state is approached. On the contrary, rheology on high DE maltodextrin (≥21) films at dry matter of 93% (w/w) suggested that drying droplets with high DE developed viscous skins, which are susceptible to surface deformations, leading to wrinkling, folding or creasing particle morphologies. The results demonstrated that DE-value may be used as an indicator for particle morphology development when interpreted in view of the process conditions.

    Enhanced nutritional value of chickpea protein concentrate by dry separation and solid state fermentation
    Xing, Qinhui ; Dekker, Susanne ; Kyriakopoulou, Konstantina ; Boom, Remko M. ; Smid, Eddy J. ; Schutyser, Maarten A.I. - \ 2020
    Innovative Food Science and Emerging Technologies 59 (2020). - ISSN 1466-8564
    Air classification - Autochthonous microbes - Pediococcus spp. - Techno-functional properties - α-Galactosides

    A sustainable dry processing method to obtain nutritional and functional chickpea products was developed, yielding protein concentrates suited to prepare products without additives. Chickpeas were milled and air-classified into protein and starch-enriched concentrates. Subsequently, spontaneous solid state fermentation (SSF) with daily back-slopping was performed at 37 °C. The dominant autochthonous lactic acid bacteria (LAB) strains in chickpea flour and enriched fractions were Pediococcus pentosaceus and Pediococcus acidilactici. Strains were selected on their ability to metabolise flatulence-causing α-galactosides. SSF reduced the pH of the doughs in 24h from 6.6 to 4.2. After 72 h, concentrations of raffinose and stachyose were reduced by 88.3–99.1%, while verbascose became undetectable. Moreover, phytic acid reduced with 17% while total phenolic contents increased with 119%. Besides the observed differences in smell, texture and colour, the sourdoughs showed 67% higher water-holding capacity. This natural route to produce chickpea concentrates thus increases both the nutritive and technical functionality. Industrial relevance Increasing the sustainability of our food production is required to meet the demand for food of our growing world population. A processing route combining dry fractionation and solid state fermentation is developed to prepare chickpea concentrates with improved nutritional properties. This route is more sustainable as the use of water and thus energy-intensive drying steps are minimised. Moreover, it provides more natural ‘clean-label’ foods, i.e., foods with less additives and minimally processed. Solid state fermentation is used to reduce the presence of anti-nutritional factors, i.e., α-galactosides and phytic acid. Autochthonous LAB were accumulated via back-slopping and employed as starter culture as an alternative to the use of a commercial starter culture. Chickpea sourdoughs with enhanced nutritional quality of chickpea were obtained. The sourdough may be used directly to fortify cereal products like chickpea protein enriched bread or can be dried into a chickpea ingredient for many other applications as well.

    Water redistribution determined by time domain NMR explains rheological properties of dense fibrous protein blends at high temperature
    Schreuders, Floor K.G. ; Bodnár, Igor ; Erni, Philipp ; Boom, Remko M. ; Goot, Atze Jan van der - \ 2020
    Food Hydrocolloids 101 (2020). - ISSN 0268-005X
    Blends of different plant proteins can form excellent basis for meat analogues by subjecting those to shear and heating. We here want to obtain more information of the internal structure of pea protein-gluten and soy protein-gluten blends, by using the polymer blending law to explain rheological responses. For this polymer blending law the water distribution over the two phases is the blend was obtained with time domain 1H NMR measurements using the NMR measurements of individual protein phases and on the blend. By matching the relaxation rate (R2) of the individual phases with those of the blend, the water distribution over the two phases could be obtained. Water is preferentially taken up by the soy or pea protein phase leaving less water for gluten, which effect strongly changes the volume fractions of the phases. Rheological properties of the separate phases as function of their hydration resulted in higher apparent modulus for the wheat gluten phase, and a lower one for the pea and soy protein phase. From the results, it was concluded that both blends show signs of a bi-continuous morphology. The SPI-WG blend showed an intermediate value between bi-continuous and SPI continuous. PPI-WG at lower temperatures showed a bi-continuous structure, while at higher processing temperatures and time was probably WG continuous.
    Multi-criteria design of membrane cascades: Selection of configurations and process parameters
    Rizki, Zulhaj ; Janssen, Anja E.M. ; Claassen, G.D.H. ; Boom, R.M. ; Padt, A. van der - \ 2020
    Separation and Purification Technology 237 (2020). - ISSN 1383-5866
    Modelling membrane cascade - Multi-criteria optimization - Set-up selection

    Membrane cascades can fractionate fructooligosaccharides into 3 different fractions with varying degrees of polymerization (DP). In contrast to the traditional membrane system, membrane cascades have flexibility in configuration and setup for each stage. Apart from the improvement flexibility of the cascades provides, it raises problems related to multiple performance indicators and multiple process parameters. Therefore, new design criteria are required. We have designed an optimization approach for this multi-criteria problem. Eight configurations of cascaded membranes were built, measured and simulated to develop a design strategy. The performance of the separation process was evaluated by 10 different indicators: purities and yields for 3 different fractions and 4 separation factors between molecules with an adjacent DP. We found that the proposed configurations exceeded the performance of the previously reported 3-stage membrane cascade. Within those configurations, the cascade designs were able to increase the purity of (1) monosaccharides to 47% from 9%, (2) DP3 to 34% from 24% and (3) DP ≥ 5 to 77% from 34%. We also report a procedure to select a single optimum combination that compromises all performance indicators. This procedure systematically calculated the weights, which were then used to rank all feasible combinations and select the best one. In addition, a backward analysis using sensitivity coefficients was performed to pinpoint critical process parameters. Knowing these parameters, more targeted and more efficient improvements could be made. This approach is applicable for most integrated systems with multi-process variables and multi-performance indicators combining process modelling and multi-criteria decision making.

    Heat-induced changes in microstructure of spray-dried plant protein isolates and its implications on in vitro gastric digestion
    Rivera del Rio, Andrea ; Opazo-Navarrete, Mauricio ; Cepero-Betancourt, Yamira ; Tabilo-Munizaga, Gipsy ; Boom, Remko M. ; Janssen, Anja E.M. - \ 2020
    Food Science and Technology = Lebensmittel-Wissenschaft und Technologie 118 (2020). - ISSN 0023-6438
    Gastric digestion - In vitro digestion - Pea protein isolate - Protein digestibility - Soy protein isolate - Spray-dried protein isolates

    The quickly expanding field of plant-based food, generally uses protein concentrates or isolates as protein source. It is however not clear to what extent the intensive processing of these raw materials affects their digestibility. We here report on the in vitro gastric digestibility of the structures present in unheated and heated dispersions of spray-dried protein isolates of soybean and yellow pea. Unheated dispersions consist primarily of insoluble individual spray-dried particles, agglomerates of these and only a small fraction of soluble protein. Pepsin activity was followed in real-time through microscopic observations, showing the disassociation of agglomerates and inward-breakdown of individual particles, which are otherwise stable at gastric pH and ionic strength. This demonstrates that solubility is not necessarily an incentive for gastric protein digestion. Heating does not significantly affect the overall digestibility of protein isolate dispersions. Nevertheless, heating disrupts the structure of spray-dried particles, increasing the amount of smaller and better digestible particles that remain suspended after centrifugation. Conversely, heat-induced aggregates remain in the pellet and are up to 50% less digestible than their unheated counterparts. This impaired digestibility is counterbalanced by a reduced proportion of poorly-digestible species in the full system (up to 11% for soy and 23% for pea).

    Drying kinetics and viscoelastic properties of concentrated thin films as a model system for spray drying
    Both, E.M. ; Tersteeg, S.M.B. ; Boom, R.M. ; Schutyser, M.A.I. - \ 2020
    Colloids and Surfaces. A: Physicochemical and Engineering Aspects 585 (2020). - ISSN 0927-7757
    Maltodextrin - Morphology - Rheology - Structural arrest - Whey protein

    Controlling the development of the particle morphology during spray drying is of large importance to obtain high quality powders. During drying of skin-forming materials it is still unknown how the rheological properties of the skin develop as a function of time, moisture content and temperature. We here studied films prepared from whey protein – maltodextrin mixtures as a model system for spray drying. The rheological properties were assessed by oscillatory shear measurements at relevant high dry matter contents (66–82 w/w%). During drying, the films high in whey protein became brittle and had slower evaporation compared to films high in maltodextrin. Rheological analysis showed that for whey protein rich systems (with higher ratio than 25:75 WP:MD) the films were in structural arrest at the dry matter contents measured. Maltodextrin films on the other hand showed typical viscoelastic polymer behavior, although as little as 1% addition of whey protein altered its viscoelastic properties drastically. The viscoelastic properties could be related to vacuole formation during single droplet drying: samples that undergo structural arrest at a lower dry matter content (high in whey protein), form less and larger vacuoles compared to samples that undergo structural arrest only at high concentration (high in maltodextrin).

    The effect of monovalent (Na+, K+) and divalent (Ca2+, Mg2+) cations on rapeseed oleosome (oil body) extraction and stability at pH 7
    Romero-Guzmán, Maria Juliana ; Petris, Vasileios ; Chirico, Simone De; Bari, Vincenzo di; Gray, David ; Boom, Remko M. ; Nikiforidis, Constantinos V. - \ 2020
    Food Chemistry 306 (2020). - ISSN 0308-8146
    Extraction - Natural emulsion - Oil bodies - Oleosomes - Rapeseed

    Oleosomes are storage vehicles of TAGs in plant seeds. They are protected with a phospholipid-protein monolayer and extracted with alkaline aqueous media; however, pH adjustment intensifies the extraction process. Therefore, the aim of this work was to investigate the extraction mechanism of rapeseed oleosomes at pH 7 and at the presence of monovalent and divalent cations (Na+, K+, Mg2+ , and Ca+2). The oleosome yield at pH 9.5 was 64 wt%, while the yield at pH 7 with H2O was just 43 wt.%. The presence of cations at pH 7, significantly enhanced the yield, with K+ giving the highest yield (64 wt.%). The cations affected the oleosome interface and their interactions. The presence of monovalent cations resulted in aggregation and minor coalescence, while divalent cations resulted in extensive coalescence. These results help to understand the interactions of oleosomes in their native matrix and design simple extraction processes at neutral conditions.

    Model development for conductive thin film drying processes
    Qiu, Jun ; Boom, Remko M. ; Schutyser, Maarten A.I. - \ 2020
    Journal of Food Engineering 268 (2020). - ISSN 0260-8774
    Conductive drying - Drum drying - Heat transfer - Process modelling - Thin film

    A heat-transfer governed model is proposed to describe drying in a lab-scale conductive thin film dryer, which was designed to investigate the drying kinetics relevant to drum drying. The model calculations were compared to experimental data from drying experiments with maltodextrin DE12 and potato starch, considering the three distinct periods (heating, boiling and conductive drying) of the lab-scale process. The model uses measured temperatures and evaporation rate during the boiling period as input to calculate the decrease in moisture content during the drying process. Model calculations were evaluated by determining the root-mean-square-error (RMSE) values. The RMSE were very small (<0.24) indicating that the model was successful in describing the film drying process. During the last drying period, the starch films exhibited a higher initial heat transfer resistance (~0.0004 (m2∙K)/W) compared to maltodextrin (~0.0002 (m2∙K)/W). This reflects the formation of larger vapour bubbles in the boiling period impeding the heat transfer for starch films. Subsequently, the model was modified to describe a pilot-scale drum drying process for maltodextrin suspensions. The initial heat transfer coefficient for drum drying of maltodextrin was obtained from the lab-scale experiments. The simulations indicated residual moisture contents and optimal drying times for different drying conditions.

    Water redistribution determined by Time Domain NMR explains rheological properties of dense fibrous protein blends at high temperature
    Schreuders, Floor ; Bodnár, Igor ; Erni, Philipp ; Boom, Remko ; Goot, Atze Jan van der - \ 2019
    A Systematic Parameter Study on Film Freeze Concentration
    Vuist, J.E. ; Schutyser, M.A.I. ; Boom, R.M. - \ 2019
    A Systematic Parameter Study on Film Freeze Concentration
    Vuist, J.E. ; Boom, R.M. ; Schutyser, M.A.I. - \ 2019
    A Systematic Parameter Study on Film Freeze Concentration
    Vuist, Jan Eise ; Schutyser, Maarten ; Boom, Remko - \ 2019
    In: 29th European Symposium on Computer Aided Process Engineering. - Elsevier B.V. (Computer Aided Chemical Engineering ) - ISBN 9780128186343 - p. 1501 - 1506.
    freeze concentration - modelling - solute inclusion

    Film freeze concentration is an alternative method to concentrate aqueous streams compared to suspension freeze concentration. Major advantage is that the equipment is less complex and thus capital costs are in principle lower. In our research we investigated especially how hydrodynamics, applied freezing temperatures and solution properties influence inclusion of solutes in ice and ice yield during film freeze concentration. For this we carried out both lab-scale experiments and CFD simulations. Model solutions of sucrose and maltodextrin were concentrated in a stirred vessel by growth of an ice layer at the bottom freezing plate. For varying stirring speeds, feed concentrations and freezing plate temperature profiles we determined the solute inclusion in the grown ice and the ice yield. When increasing stirrer speeds a decreasing amount of solute included in ice was found at constant freezing plate temperature. This can be explained because the transport of the solute molecules in the boundary layer is diffusion limited. An increase in shear above the surface reduces the thickness of this layer and therefore less solute is included in ice at high shear rates. CFD simulations were carried out to describe the hydrodynamics near the surface and to relate the shear rate to the impeller Reynolds number. Moreover, the CFD simulations could explain the increased solute inclusions for higher concentrations of sucrose as higher viscosities lead to significant reduction of shear rates close to the ice layer. The CFD simulations will facilitate easier translation of the obtained results for a differently designed film freeze concentration system. Sucrose and maltodextrin appeared to behave very similar with respect to inclusion behaviour, which may be explained from their similar diffusivities. Ice growth rate is found another important factor and is very much influence by applied freezing temperatures. Our experiments showed that there is a critical ice growth rate. If this ice growth rate is exceeded more solutes will be included in the ice layer. In this case the solute molecules will not have the chance to move away from the ice boundary. The next step in our research is modelling of the ice growth rate as function of the freezing plate temperature to optimise both ice yield and solute inclusion.

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