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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    Premix emulsification systems
    Nazir, A. - \ 2013
    Wageningen University. Promotor(en): Karin Schroen; Remko Boom. - S.l. : s.n. - ISBN 9789461735157 - 151
    emulgering - emulgeren - emulsies - kunstmatige membranen - vervuiling door afzetting - poriëngrootte - zeven - emulsification - emulsifying - emulsions - artificial membranes - fouling - pore size - sieves

    Emulsions are dispersions of two (or more) immiscible liquids (e.g., oil and water), and are widely used in various industries including food, cosmetics, pharmaceutics, etc. Premix membrane emulsification is an interesting technique for the controlled production of small and uniformly sized droplets. In this process, a coarse emulsion (premix) is first prepared which is then passed under mild pressure through a (microporous) membrane. Due to its high throughputs, the premix emulsification is a promising process, however, the internal fouling is the most important drawback. The research descripted in this thesis aimed to better understand the fundamental limitations in this process, and to find a solution to this, by either reducing fouling by using well-defined membranes, or by making use of a dynamic membrane in the form of packed bed. Furthermore, new designs for continuous operation for emulsification and foam formation are presented. Based on the obtained results, the proposed technologies in this thesis are expected to have significant industrial application.

    Physico-chemical and techno-functional properties of proteins isolated from the green microalgae Tetraselmis sp.
    Schwenzfeier, A. - \ 2013
    Wageningen University. Promotor(en): Harry Gruppen, co-promotor(en): Peter Wierenga; Michel Eppink. - S.l. : s.n. - ISBN 9789461734532 - 132
    algen - eiwitten - functionele eigenschappen - schuimen - emulgeren - emulsies - algae - proteins - functional properties - foaming - emulsifying - emulsions

    In this thesis, the mild isolation of an algae soluble protein isolate (ASPI) and the characterisation of its techno-functional properties are described. The ASPI was isolated from the green microalgae Tetraselmis sp. by beadmilling and subsequent anion exchange adsorption. The isolate obtained contained 59 ± 7% (w/w) protein and 20 ± 6% (w/w) carbohydrates, the latter composed for approximately one fourth of uronic acids (4.8 ± 0.4% [w/w]). In the pH range 5.5 – 6.5, in which currently used legumin seed protein isolates (e.g. soy) show low solubility, ASPI retained high solubility independent of ionic strength. In the soluble pH range, the foam stability of ASPI is superior to the foam stabilities of whey protein isolate (WPI) and egg white albumin (EWA). At pH 7, ASPI stabilized foams are 1.7 times more stable than WPI stabilized foams. Further fractionation of APSI results in foams even 3 times more stable than WPI stabilized foams. In addition, emulsions stabilised with ASPI are stable against droplet aggregation around pH 5 at low ionic strength, while emulsions stabilised by WPI are not stable at this pH. The stability of ASPI emulsions at this pH is attributed to the co-adsorption of the charged polysaccharide fraction present in ASPI. The role of the charged polysaccharides on stabilisation of the emulsions was confirmed by fractionating ASPI into protein-rich and charged polysaccharide-rich fractions. The combination of charged polysaccharides and proteins in ASPI results in good techno-functional properties that are between that of pure proteins and that of the naturally occurring protein-polysaccharide hybrid gum arabic (GA). It is concluded that ASPI represents an attractive substitute for currently used high-value food protein isolates. Due to the combination of the positive interfacial properties of its protein fraction with the broad pH stability of its charged polysaccharide fraction, ASPI possesses the positive attributes of two types of techno-functional ingredients.

    Microtechnologie voor minder vette mayonaise
    Dijke, K.C. van - \ 2010
    Chemie Magazine 2010 (2010)1. - ISSN 1572-2996 - p. 13 - 13.
    voedseltechnologie - emulsies - emulgeren - vetemulsies - vetarme producten - microtechnieken - voedselemulsies - voeding en gezondheid - food technology - emulsions - emulsifying - fat emulsions - low fat products - microtechniques - food emulsions - nutrition and health
    De Wageningse onderzoeker dr. ir. Koen van Dijke ontwikkelde een nieuw microtechnologisch concept voor de vorming van emulsies: EDGE (Edge based Droplet Generation). Het maakt de emulsificatie beter beheersbaar en energie-efficiënter. Bovendien kunnen er dubbelemulsies mee gemaakt worden voor een romige maar toch vetarme mayonaise
    Emulsification in microfluidic Y- and T-junctions
    Steegmans, M.L.J. - \ 2009
    Wageningen University. Promotor(en): Remko Boom, co-promotor(en): Karin Schroen. - [S.l. : S.n. - ISBN 9789085854579 - 150
    emulsies - emulgering - emulgeren - druppelgrootte - emulsions - emulsification - emulsifying - droplet size
    On a daily basis, we encounter many emulsion-based products such as butter or sun cream, which consist of oil droplets in water, or water droplets in oil. Traditionally, these emulsions are produced with systems that allow a high throughput, but yield a broad droplet size distribution. Therefore, the industry is interested in emulsification techniques that give more monodisperse emulsions, such as emulsification with microfluidic devices, i.e. defined geometries with channel diameters in the order of several to hundreds of micrometers.

    The goal of this thesis was to develop a new microfluidic emulsification technique that has the potential to be scaled up for the production of large volumes of monodisperse emulsion. We chose to study shear-driven microfluidic devices, i.e. T- and Y-junctions, due to their high productivity per junction and their potential for mass-parallelisation. However, reliable application of these junctions is only possible when the droplet-formation mechanism and droplet size determining parameters are fully understood. Therefore, we took a single junction both as a starting and as a focal point of this thesis.

    The thesis starts off by indicating and quantifying the parameters that determine droplet size in microfluidic T-junctions. In literature, (monodisperse) emulsification at T-junctions is studied for a broad range of channel dimensions, flow rates, and materials. However, it is not yet clear which parameters determine the droplet size. Therefore, in Chapter 2 statistical analysis is used to quantitatively relate droplet size data from various literature sources. For T-junctions it is found that emulsion droplet size of drops, discs, and plugs can be described by a two-step model consisting of a droplet growth and a droplet detachment step. This suggests that an emulsion droplet grows until a certain volume is reached, after which it starts to detach. The channel dimensions determine droplet growth, while the continuous- and the disperse-phase flow rate determine the abating time (i.e. the fast decrease of the neck resulting in detachment).

    In the remainder of this thesis microfluidic (flat) Y-junctions are discussed; they resemble T-junctions, but are hardly studied in literature. In Chapter 3, emulsification of hexadecane in various ethanol-water mixtures at different process conditions, i.e. flow rates and static interfacial tensions, is experimentally investigated. We focus on droplet formation at the Y-junction or downstream without the incipient droplet blocking the downstream channel (i.e. the dripping and the jetting regime). For Y-junctions, the droplet size is described with a force balance between the interfacial tension force and the shear force at the point where the incipient droplet is kept to the bulk by a neck. It is found that the droplet size at Y-junctions is determined by the interfacial tension, the channel dimensions, and the viscosity and flow rate of the continuous phase; but not by the flow rate of the disperse phase. This makes operation of Y-junctions intrinsically easier than T-junctions, for which the flow rates of both phases need to be (accurately) controlled.

    Where Chapter 3 concentrates on process conditions, in Chapter 4 the effect of (Y-) junction design on the droplet size is investigated. In five different Y-junction geometries and one T-junction with a depth of 5 m, hexadecane is emulsified in ethanol-water mixtures at a given static interfacial tension and at various process conditions, e.g. flow rates. For the various Y-junctions, no effect on droplet size is observed from the junction angle and the length(s) and/or the width(s) of the microchannel(s). In contrast, significant differences are observed between T- and Y-junctions.

    In Chapter 5, the force balance, found in Chapter 3, is extended by including the effect of the viscosity of the disperse phase and a broader range of viscosities and/or flow rates of the continuous phase. The force balance is mainly adapted by rewriting the shear force from the drag force on a sphere to the drag force on the cross-sectional area of the squeezed incipient droplet (head). It is found that the emulsion droplet size at Y-junctions is determined by the interfacial tension, the channel dimensions, the viscosity, density, and flow rate of the continuous phase, and the resistance with the wall. The influence of the viscosity of the disperse phase and the viscosity ratio were found negligible, just as the disperse-phase flow rate.

    The first five chapters show that droplet size at microfluidic Y-junctions is strongly influenced by the interfacial tension and therefore it is important to quantify its value under dynamic conditions. Traditional tensiometric techniques do not allow interfacial tension measurement under the conditions applied in Y-junctions: high shear and droplet formation in less than milliseconds. Therefore, in Chapter 6, (monodisperse) emulsification at microfluidic Y-junctions is proposed as a new tensiometric technique. A calibration curve is derived for hexadecane in various ethanol-water mixtures with a range of static interfacial tensions. Subsequently, this curve is used to estimate the apparent dynamic interfacial tension for solutions with the surfactants SDS or Synperonic PEF108. The apparent dynamic interfacial tension is found to be determined by the flow rates of the continuous and disperse phase, the surfactant and its concentration. In addition, we showed that surfactant transport in Y-junctions is dominated by convection.

    In Chapter 7, the thesis is concluded by comparing emulsification with microfluidic Y-junctions to other shear-driven microfluidic geometries with cross-flow membrane emulsification as a benchmark technology. Especially, the negligible effect of the flow rate and the viscosity of the disperse phase on the droplet size makes microfluidic Y-junctions unique. To illustrate the large-scale feasibility of microfluidic Y-junctions, typical emulsification device volumes and required areas to process 1 m3h-1 of disperse phase were calculated. The requirements are found to be comparable to values obtained from literature for membranes and microsieves. The energy input of the current microfluidic Y-junction design is comparable to traditional emulsification techniques, but since there is room for optimisation, we are hopeful that these values may well be reduced.

    Emulsification with microstructured systems : process principles
    Zwan, E.A. van der - \ 2008
    Wageningen University. Promotor(en): Remko Boom, co-promotor(en): Karin Schroen. - [S.l.] : S.n. - ISBN 9789085049234 - 119
    emulgering - emulgeren - emulsies - membranen - microporiën - filterbedden - druppelgrootte - kunstmatige membranen - emulsification - emulsifying - emulsions - membranes - micropores - filter beds - droplet size - artificial membranes
    The aim of this thesis is to elucidate the underlying processes and mechanisms that determine the droplet size of emulsions produced with microstructured systems, such as premix microstructure homogenization and microchannel emulsification. The ultimate goal is to describe these methods based on detailed knowledge on droplet break-up and droplet formation mechanisms. This includes, amongst others, the influence of viscosity of the (to-be) dispersed and continuous phase, interfacial tension, velocity, and the geometry of the system on droplet break-up and formation. This was done both computationally and experimentally. The insight that was generated was translated into several design rules that can be used for optimization.
    Physico-chemical and functional properties of sunflower proteins
    Gonzalez-Perez, S. - \ 2003
    Wageningen University. Promotor(en): Fons Voragen, co-promotor(en): Harry Gruppen; A.L.J. Vereijken. - [S.l.] : S.n. - ISBN 9789058089045 - 145
    zonnebloemeiwit - fysicochemische eigenschappen - denaturatie - oplosbaarheid - schuimen - schuim - emulgeren - emulsies - sunflower protein - physicochemical properties - denaturation - solubility - foaming - foams - emulsifying - emulsions
    Keywords: Sunflower protein, Helianthusannuus ,helianthinin, albumins, solubility, structure,denaturation, pH, temperature, ionic strength,phenoliccompounds,chlorogenicacid, foams, emulsions, functionality

    The research described in this thesis deals with the relation between specific sunflower proteins, their structure and their functional properties as a function of extrinsic factors as pH, ionic strength and temperature.

    Sunflower protein isolate (SI) devoid ofchlorogenicacid (CGA), the mainphenoliccompound present, was obtained withoutdenaturationof the proteins. Sunflower proteins were found to be composed of two main protein fractions: 2S albumins or sunflower albumins (SFAs) andhelianthinin. Subsequently, these protein fractions werebiochemicallyand structurally characterized under conditions relevant to food processing.

    Depending on pH, ionic strength, temperature and protein concentration,helianthininoccurs in the 15-18S (high molecular weight aggregate), 11 S (hexamer), 7S (trimer) or 2-3S (monomer) form. Dissociation into 7S from 11S gradually increased with increasing pH from 5.8 to 9.0. Enhancing the ionicstrengthresulted in stabilization of the 11S form. Heating and lowering the pH resulted in dissociation into themonomericform ofhelianthinin. The 11S and 7S form ofhelianthinindiffer in their secondary structure, tertiary structure, and thermal stability. With respect to solubilityas a function of pH,helianthininshows a bell shaped curve with a minimum at approximately pH 5.0 at low ionic strength. At high ionic strength,helianthininis almost insoluble at pH< 5.0.

    The second main sunflower fraction,SFAs, revealed to be very stable against pH changes (pH 3.0 to 9.0) and heat treatment (up to 100°C), and their solubility was only marginally affected by pH and ionic strength. The solubility of the SI as a function of pH seems to be dominated by that ofhelianthinin.

    Foam and emulsion properties of the sunflower isolate as well as those of purifiedhelianthinin,SFAsand combinations thereof were studied at various pH values and ionic strengths, and after heat treatment. Sunflower proteins were shown to form stable emulsions, with the exception ofSFAsat alkaline and neutral pH values. Increasing amount ofSFAsimpaired the emulsifying properties. Regarding foam properties, less foam could be formed fromhelianthininthan fromSFAs, but foam prepared withhelianthininwas more stable againstOstwaldripening and drainage than foam prepared withSFAs. Increasing amounts ofSFAshad a positive effect on foam volume and a negative one on foam stability and drainage. It was found that treatments that increase conformational flexibility improve the emulsion and foam properties of sunflower proteins.
    Emulsies uit membranen
    Boom, R.M. ; Gijsbertsen-Abrahamse, A.J. ; Schroën, C.G.P.H. - \ 2003
    Voedingsmiddelentechnologie 36 (2003)14/15. - ISSN 0042-7934 - p. 14 - 16.
    emulgeren - emulsies - membranen - energie - besparingen - conferenties - voedselindustrie - voedseltechnologie - emulgering - emulsifying - emulsions - membranes - energy - savings - conferences - food industry - food technology - emulsification
    Membraanemulgeren is een veelbelovende jonge techniek waarbij met weinig energie een betere productkwaliteit wordt verkregen. Op 4 juni werd door onderzoeksschool VLAG in Wageningen een themadag georganiseerd over het betreffende onderwerp. De aanleiding to deze dag was de promotie van ir. A. Gijsbertsen - Abrahamse. Zij promoveerde als eerste in Nederland op deze nieuwe techniek
    Membrane emulsification: process principles
    Gijsbertsen-Abrahamse, A.J. - \ 2003
    Wageningen University. Promotor(en): Remko Boom, co-promotor(en): A. van der Padt. - [S.I.] : S.n. - ISBN 9789058088451 - 104
    emulsies - emulgeren - membranen - druppelstudies - computationele vloeistofdynamica - emulsions - emulsifying - membranes - droplet studies - computational fluid dynamics
    With membrane emulsification in principle monodisperse emulsions can be produced, requiring a relatively low energy density which implies that the shear stress exerted on the ingredients is low. In membrane emulsification the to-be-dispersed phase is pressed through the membrane pores; under certain conditions droplets are formed at the membrane surface. In cross-flow membrane emulsification the droplets are detached by the continuous phase flowing across the membrane surface. A limiting factor for emulsion production on a commercial scale will be a low disperse phase flux. Better knowledge of how membrane parameters affect the disperse phase flux would enable the targeted development of membranes, optimal for the process of cross-flow membrane emulsification for a given application. Therefore, the objective of this research is to gain a fundamental understanding of the mechanism of droplet formation at the membrane surface and of the flow of the disperse phase through the membrane as a function of the membrane characteristics.
    Droplet formation was studied at a microscopic level with computational fluid dynamics (CFD) simulations and by microscopic experiments of droplet formation at a very thin microsieve with uniform pores. Since these membranes are extremely well defined, they are a good model system for detailed study. Results from both simulations and experiments indicate that to prevent coalescence and steric hindrance of droplets, the membrane porosity should be very low. Steric hindrance resulted in polydisperse emulsions and led to coupling of droplet detachment from neighboring pores. Furthermore, although the pores all had the same diameter, the number of pores at which droplets were formed only increased gradually with increasing transmembrane pressure. This effect was further studied with a scaled-up analogon and could be modeled by taking the resistance of the pores and the resistance of a membrane substructure into account. This model is compared with a model for flow through an isotropic membrane with interconnected uniform pores and extended to describe flow through a membrane with a pore size distribution. This model is used to show that in most cases the estimation of a membrane pore size distribution by using the liquid displacement method is not correct. Just as in membrane emulsification, pores become active at higher transmembrane pressures than expected. Finally, the effects of several membrane parameters on membrane emulsification performance are summarized. As an example, the membrane area required for a typical industrial application is estimated using the models mentioned above, for different types of membranes.
    Soy proteins : nomenclature, composition, structure and functionality
    Vereijken, J.M. - \ 2000
    Industrial Proteins 8 (2000)3. - ISSN 1381-0022 - p. 3 - 5.
    sojaeiwit - peulvruchteiwit - sojabonen - botanische samenstelling - structuur - structuuractiviteitsrelaties - emulgeren - eiwitten - globulinen - literatuuroverzichten - eiwittechnologie - soya protein - legume protein - soyabeans - botanical composition - structure - structure activity relationships - emulsifying - proteins - globulins - literature reviews - protein engineering
    De structuur van de belangrijkste soja-eiwitten is beschreven evenals hun verschil in functionaliteit
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