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.

    All-aqueous emulsions as miniaturized chemical reactors in the food and bioprocess technology
    Madadlou, Ashkan ; Saggiomo, Vittorio ; Schroën, Karin ; Fogliano, Vincenzo - \ 2020
    Current Opinion in Food Science (2020). - ISSN 2214-7993
    All-aqueous emulsions are conventionally formed at bulk scale by mild shaking of aqueous two-phase systems. They can be used to carry out reactions both in droplets (compartmentalized) and on droplet surfaces in conditions free of synthetic surfactants and organic solvents. The use of all-aqueous emulsions for extractive bioconversion is a routine application; however, these emulsions hold many more promises. A renowned, rapidly evolving application is bio-microgel synthesis through biopolymer crosslinking within the emulsion internal phase. When polyelectrolyte crosslinking is achieved at the interface rather than in droplets, microcapsules can be formed, and when in situ colloidal particle generation at the droplet surface is obtained, colloidosomes are produced. The use of microfluidics to control the formation of all-aqueous emulsions offers many advantages in reactions monitoring and partitioning of reactants.
    Behavior of plant-dairy protein blends at air-water and oil-water interfaces
    Hinderink, E.B.A. ; Sagis, L.M.C. ; Schroen, C.G.P.H. ; Berton-Carabin, C.C. - \ 2020
    Colloids and Surfaces. B: Biointerfaces 192 (2020). - ISSN 0927-7765 - 10 p.
    Interfacial rheology - lissajous plot - interface characterization - plant protein - dairy protein - Protein mixtures
    Recent work suggests that using blends of dairy and plant proteins could be a promising way to mitigate sustainability and functionality concerns. Many proteins form viscoelastic layers at fluid interfaces and provide physical stabilization to emulsion droplets; yet, the interfacial behavior of animal-plant protein blends is greatly underexplored. In the present work, we considered pea protein isolate (PPI) as a model legume protein, which was blended with well-studied dairy proteins (whey protein isolate (WPI) or sodium caseinate (SC)). We performed dilatational rheology at the air-water and oil-water interface using an automated drop tensiometer to chart the behavior and structure of the interfacial films, and to highlight differences between films made with either blends, or their constituting components only. The rheological response of the blend-stabilized interfaces deviated from what could be expected from averaging those of the individual proteins and depended on the proteins used; e.g. at the air-water interface, the response of the caseinate-pea protein blend was similar to that of PPI only. At the oil-water interface, the PPI and WPI-PPI interfaces gave comparable responses upon deformation and formed less elastic layers compared to the WPI-stabilized interface. Blending SC with PPI gave stronger interfacial layers compared to SC alone, but the layers were less stiff compared to the layers formed with WPI, PPI and WPI-PPI. In general, higher elastic moduli and more rigid interfacial layers were formed at the air-water interface, compared to the oil-water interface, except for PPI.
    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.
    Pickering particles as interfacial reservoirs of antioxidants
    Schröder, Anja ; Laguerre, Mickaël ; Sprakel, Joris ; Schroën, Karin ; Berton-Carabin, Claire C. - \ 2020
    Journal of Colloid and Interface Science 575 (2020). - ISSN 0021-9797 - p. 489 - 498.
    Biobased particle - Encapsulation - Fat crystal - Interface - Lipid oxidation - Lipophilic antioxidant - Natural bioactive - Pickering emulsion - α-tocopherol

    Hypothesis: Emulsions are common structures encapsulating lipophilic bioactive molecules, both in biological systems and in manufactured products. Protecting these functional molecules from oxidation is essential; Nature excels at doing so by placing antioxidants at the oil-water interface, where oxidative reactions primarily occur. We imagined a novel approach to boost the activity of antioxidants in designer emulsions by employing Pickering particles that act both as physical emulsion stabilizers and as interfacial reservoirs of antioxidants. Experiments: α-Tocopherol or carnosic acid, two model lipophilic antioxidants, were entrapped in colloidal lipid particles (CLPs) that were next used to physically stabilize sunflower oil-in-water emulsions (“concept” Pickering emulsions). We first assessed the physical properties and stability of the CLPs and of the Pickering emulsions. We then monitored the oxidative stability of the concept emulsions upon incubation, and compared it to that of control emulsions of similar structure, yet with the antioxidant present in the oil droplet interior. Findings: Both tested antioxidants are largely more effective when loaded within Pickering particles than when solubilized in the oil droplet interior, thus confirming the importance of the interfacial localization of antioxidants. This approach revisits the paradigm for lipid oxidation prevention in emulsions and offers potential for many applications.

    Chemical Stability of α-Tocopherol in Colloidal Lipid Particles with Various Morphologies
    Schröder, Anja ; Sprakel, Joris ; Schroën, Karin ; Berton-Carabin, Claire C. - \ 2020
    European Journal of Lipid Science and Technology 122 (2020)6. - ISSN 1438-7697
    encapsulation - lipid crystallization - lipophilic bioactives - solid lipid nanoparticles - vitamin E

    Colloidal lipid particles (CLPs) are promising encapsulation systems for lipophilic bioactives, such as oil-soluble antioxidants that are applied in food and pharmaceutical formulations. Currently, there is no clear consensus regarding the relation between particle structure and the chemical stability of such bioactives. Using α-tocopherol as a model antioxidant, it is shown that emulsifier type (Tween 20 or 40, or sodium caseinate) and lipid composition (tripalmitin, tricaprylin, or combinations thereof) modulated particle morphology and antioxidant stability. The emulsifier affects particle shape, with the polysorbates facilitating tripalmitin crystallization into highly ordered lath-like particles, and sodium caseinate resulting in less ordered spherical particles. The fastest degradation of α-tocopherol is observed in tripalmitin-based CLPs, which may be attributed to its expulsion to the particle surface induced by lipid crystallization. This effect is stronger in CLPs stabilized by Tween 40, which may act as a template for crystallization. This work not only shows how the architecture of CLPs can be controlled through the type of lipid and emulsifier used, but also gives evidence that lipid crystallization does not necessarily protect entrapped lipophilic bioactives, which is an important clue for encapsulation system design. Practical Applications: Interest in enriching food and pharmaceutical products with lipophilic bioactives such as antioxidants through encapsulation in lipid particles is growing rapidly. This research suggests that for efficient encapsulation, the particle architecture plays an important role; to tailor this, the contribution of both the lipid carrier and the emulsifier needs to be considered.

    Microtechnological Tools to Achieve Sustainable Food Processes, Products, and Ingredients
    Schroën, Karin ; Ruiter, Jolet de; Berton-Carabin, Claire C. - \ 2020
    Food Engineering Reviews 12 (2020). - ISSN 1866-7910 - p. 101 - 120.
    Emulsification - Filtration - Functionality testing - Ingredient fractionation - Microfluidics - Microtechnology - Organs on chip - Protein transition - Sensors - Sustainable food design

    One of the major challenges we face as humankind is supplying a growing world population with sufficient and healthy foods. Although from a worldwide perspective sufficient food is produced, locally, the situation can be dire. Furthermore, the production needs to be increased in a sustainable manner for future generations, which also implies prevention of food waste, and making better use of the available resources. How to contribute to this as food technologists is an ultimate question, especially since the tools that can investigate processes at relevant time scales, and dimensions, are lacking. Here we propose the use of microtechnology and show examples of how this has led to new insights in the fields of ingredient isolation (filtration), and emulsion/foam formation, which will ultimately lead to better-defined products. Furthermore, microfluidic tools have been applied for testing ingredient functionality, and for this, various examples are discussed that will expectedly contribute to making better use of more sustainably sourced starting materials (e.g., novel protein sources). This review will wrap up with a section in which we discuss future developments. We expect that it will be possible to link food properties to the effects that foods create in vivo. We thus expand the scope of this review that is technical in nature, toward physiological functionality, and ultimately to rational food design that is targeted to improve human health.

    Separation kinetics and phase behaviour of volatile flavour active compounds in aqueous food streams
    Ammari, Ali - \ 2020
    Wageningen University. Promotor(en): C.G.P.H. Schroen; R. Boom. - Wageningen : Wageningen University - ISBN 9789463953511 - 119

    Volatile organic compounds (VOC) present at low concentrations may have a tremendous effect on the flavour profile of e.g. fermented beverages such as wine and beer. Controlling the flavour profile requires a detailed understanding of the physiochemical interactions of these components with the food matrices in which they occur. This thesis tries to answer the question of whether it   is possible to separate any of the major volatile flavours in lager beers, especially isoamyl acetate. The proposed technique to do so had to meet a series of criteria. It had to be mild to protect biological ingredients such as proteins from being damaged, be able to handle high throughput (~100 to 500 m3/hr), satisfy food-grade conditions and must be compatible with current flavour stripping processes. To design such a process, more fundamental knowledge was needed,  especially regarding the thermodynamics of solutions and kinetics of separation. These two topics are therefore addressed throughout the thesis.

    In chapter II we start with a critical review of the current knowledge on flavour-matrix interactions in aqueous systems. We found that the fundamental data needed to design flavour separation processes for beer have neither been investigated experimentally nor through predictive modelling. The main focus in most papers was on the sensory aspects of flavour retention and release and directly linked to food design, and not to flavour design. Along with providing the first results from our work, we discussed and challenged the experimental techniques and data interpretation methods that are currently common practice, and recommended techniques to avoid pitfalls.

    Based on our observations in chapter 2, we quantified Henry’s Law Constant (HLC) in chapter   III for the three major flavour compounds in beer (ethyl acetate, isoamyl acetate and isoamyl alcohol) in a model system containing ethanol concentrations below 25 %(v/v). We used the   static headspace analysis method and showed that a major effect on flavour retention takes place  at ethanol concentrations between 15 and 20 %(v/v) and higher. We also modelled this   behaviour using Henry coefficients for aqueous binary, and ternary systems using the Wohl expansion for excess Gibbs free energy coupled with the one-parameter Margules equation. The first approach was not complex enough to cover the behaviour of the components, but based on the second model, we could. Wohl’s expansion parameter for ethanol-water can be interpreted as solvent-solvent interaction. Furthermore, we quantified HLCs based on Van ’t Hoff parameters between 30 to 60˚C.

    In chapter IV, we used a stripping column with structural packing to observe the effect of beer  dry matter on flavour behaviour. We observed that the major components are carbohydrates and small proteins that in general enhance migration of esters from the aqueous body of the beer. However, there was a slight retention of isoamyl alcohol that was due to changes in mass transfer resistance. The effect of gas flow rate on the partition coefficient of the compounds was minor,  but it almost doubled the mass transfer coefficient of volatile flavour compounds. For isoamyl alcohol, the mass transfer resistance was found to be in both phases whereas for ester groups and ethanol the major resistance is in the gas phase which explains the difference in behaviour.

    In chapter V we examined the possibility of using frictional diffusion (FricDiff) for separation of volatile compounds from a model gas mixture as it may exit a stripping column operating with carbon dioxide. We showed that a flat sheet FricDiff module can separate isoamyl acetate from  the gas feed and that the presence of water or ethanol on the sweep side creates additional   friction on flavour compounds and thus enhances separation but not enough to retain them completely. This may be further improved by adding flavours to the sweep gas, or alternatively,  the thickness of the membrane and the pore size would need to be adjusted, which in turn would theoretically also improve the selectivity of the process in absence of wall friction.

    In the general discussion (chapter VI), we bring all the findings presented earlier together and wrap up with recommendations for process design.

    Combined physical and oxidative stability of food Pickering emulsions
    Schröder, Anja - \ 2020
    Wageningen University. Promotor(en): C.G.P.H. Schroën, co-promotor(en): C.C. Berton-Carabin; J.H.B. Sprakel. - Wageningen : Wageningen University - ISBN 9789463951968 - 251

    Many food products contain lipid droplets dispersed in an aqueous phase (e.g., milk, mayonnaise), thus are oil-in-water (O/W) emulsions. Food emulsions may be subjected to destabilization, both from a physical and a chemical perspective. Physical destabilization is generally prevented by the use of conventional emulsifiers such as surfactants and proteins. Chemical destabilization, in particular lipid oxidation, is a major concern in food products, especially when healthy polyunsaturated fatty acids are present, and this degradation is usually mitigated by the use of synthetic antioxidants, often in large amounts.

    The use of alternative ingredients for the formulation of food emulsions has been emerging, for example solid particles (so-called Pickering particles, that are very popular nowadays) that irreversibly adsorb to the interface and therewith provide high physical stability; or natural antioxidants such as tocopherols and rosemary extracts, which are attractive in the current clean-label trend to prevent lipid oxidation. The efficiency of these natural antioxidants is unfortunately often not optimal, which can be explained by their tendency to locate into the oil or water phase, whereas lipid oxidation is initiated at the oil-water interface, and thus is the place where antioxidants should be located to optimally exert their protective effect.

    The objective of this project was to develop food emulsions with a new and controlled architecture directed at yielding both excellent physical and oxidative stability. In these emulsions the oil droplets were covered by food-grade Pickering particles that exert a double role: they act as physical stabilizers, and as a reservoir for antioxidant molecules located close to the oil-water interface, therewith preventing the first lipid oxidation events, which is expected to drastically enhance antioxidant activity.

    The first part of this thesis focused on the preparation and characterization of a new food-grade lipid-based Pickering particles, referred to as colloidal lipid particles (CLPs). We prepared both surfactant-covered and protein-covered CLPs, and found that the type of emulsifier largely determined their morphology: protein-covered CLPs were roughly spherical, whereas surfactant-covered CLPs looked more lath-like (Chapters 3 and 6). We also showed that the lipid material alters the crystal polymorphism and subsequent CLP structure, which consequently influenced their performance as emulsion stabilizers (Chapter 3). For instance, surfactant-covered CLPs containing only high melting point lipids showed highly ordered crystalline structures, and formed jammed, cohesive interfacial layers once adsorbed onto oil droplets, whereas the ones containing a fraction of low melting point lipids showed less ordered crystalline structures and formed thin and bridged layers.

    Since protein-covered CLPs were particularly resilient to subsequent emulsification processes, these particles were used to study the formation of emulsion droplets in a microfluidic device and their stability to short-term coalescence (Chapter 4). We found a non-monotonic dependency of the droplet stability on the particle concentration: at low surface coverage, CLPs had a destabilizing effect as incompletely covered surfaces led to droplet-droplet bridging and subsequent coalescence, whereas at higher surface coverage, particles formed an effective barrier against droplet coalescence, resulting in physically stable emulsions over the time scales probed.

    As a next step, we investigated lipid oxidation in Pickering emulsions stabilized by protein-based CLPs that did not contain antioxidants (Chapter 5). We showed that these Pickering emulsions had a similar oxidative stability as conventional protein-stabilized emulsions for a similar composition of the oil droplets. Yet, when in both emulsions the same amount of solid lipids was present (either as stabilizing CLPs, or within the oil droplet core), a Pickering emulsion had a higher physicochemical stability. This shows that the location of crystallizable lipids influences lipid oxidation in O/W emulsions, and thus needs to be carefully considered in emulsion design.

    CLPs that did contain the lipophilic antioxidant α-tocopherol are presented in Chapter 6. The chemical stability of α-tocopherol was negatively influenced by lipid crystallization that probably promoted the localization of α-tocopherol close to the particle surface, which was further enhanced by emulsifiers that actively induce lipid crystallization. When applied as Pickering stabilizers in O/W emulsions (Chapter 7), lipid oxidation was reduced compared to control emulsions with the same composition and structure, but where the antioxidant was present in the core of the oil droplets. This confirmed that the interfacial localization of the antioxidant is crucial to prevent lipid oxidation in emulsions, and that the two main instability issues (i.e., physical and chemical instability) of emulsions can be mitigated through one single approach.

    After establishing the proof of concept with the CLPs, we used biobased particles (that may contain antioxidants) from various natural sources to stabilize O/W emulsions (Chapter 8). Emulsions stabilized by matcha tea powder or spinach leaf powder were both highly physically and oxidatively stable, which shows that the double functionality that we achieved using purposely built particles (CLPs) can also be achieved with naturally occurring particles.

    In the general discussion of the thesis (Chapter 9) we describe that the dual functionality of CLPs can also be reached using other food components, which makes this approach a generic one. We expect that the system could be further improved, for example, by increasing the residence time of antioxidants at the interface. To do so, we probably need to link the time scale at which the relevant oxidation events occur with those during which the antioxidant actually resides at the interface. Follow-up research on entrapment of antioxidants within particles is needed to reach long residence times at the interface while not compromising the ability of antioxidants to exert their chemical activity. To conclude: through our approach the highly-stable food emulsions of the future may come within reach.

    Emulsion comprising antioxidant particles
    Schroder, A.J. ; Sprakel, J.H.B. ; Schroen, C.G.P.H. ; Berton-Carabin, C.C. ; Laguerre, Mickael ; Birtic, Simona - \ 2020
    Octrooinummer: WO2020007885, gepubliceerd: 2020-01-09.
    The present invention relates to compositions comprising particles prepared from one or more biological materials and/or animal lipids and/or plant lipids that are capable of locating to an interface when combined with two or more immiscible liquids. Emulsions comprising the compositions comprising particles, wherein the emulsion has an internal phase dispersed in a continuous external phase and the particles are located at the interface of the external and the internal phase, methods of preparing such compositions and emulsions, the use of such compositions and emulsions and products containing the compositions and emulsions are also described.
    Wat met de alcohol uit de o,o biertjes?
    Schroen, Karin - \ 2020
    Microfluidic investigation of the coalescence susceptibility of pea protein-stabilised emulsions: Effect of protein oxidation level
    Hinderink, E.B.A. ; Kaade, Wael ; Sagis, L.M.C. ; Schroen, C.G.P.H. ; Berton-Carabin, C.C. - \ 2020
    Food Hydrocolloids 102 (2020). - ISSN 0268-005X - 10 p.
    Plant proteins - Emulsion stability - Emulsification - langmuir-blodgett-films
    Proteins are used to stabilise oil-in-water (O/W) emulsions, and plant proteins are gaining interest as functional ingredients due to their higher sustainability potential compared to e.g., dairy proteins. However, their emulsifying properties are not that well understood, and depend on how their production process affects their physicochemical status. In the present work, we use the soluble fraction of commercial pea protein isolate to stabilise O/W emulsion droplets formed in a microfluidic device, and record coalescence stability after droplet formation (11–173 ms) for different protein concentrations (0.1–1 g/L). For the shortest adsorption times (11–65 ms) droplets were unstable, whereas for longer adsorption times differences in coalescence stability could be charted. Metal-catalysed oxidation of pea proteins performed for up to 24-h, prior to emulsion formation and analysis, increased the coalescence stability of the droplets, compared to fresh pea proteins. This may be explained by oxidation-induced protein fragmentation, leading to low molecular weight products. The Langmuir-Blodgett films looked highly heterogeneous for films prepared with fresh or mildly oxidised (3-h) proteins, and was more homogenous for 24-h oxidised proteins. This could be the cause for the observed differences in emulsion coalescence stability, structurally heterogeneous films being more prone to rupture. From this work, it is clear that the emulsifying properties of pea are strongly dependent on their chemical status, and associated structural properties at the molecular and supramolecular levels. The present microfluidic device is an efficient tool to capture such effects, at time scales that are relevant to industrial emulsification.
    Electrochemical separation: from ions to proteins
    Fritz, Pina Atalanta - \ 2019
    Wageningen University. Promotor(en): Karin Schroën; Remko Boom, co-promotor(en): Mary B. Chan-Park. - Wageningen : Wageningen University - ISBN 9789463951272 - 209

    Separation process are at the heart of many industries ranging from chemical to medical and food. To create innovative products, first specific components need to be purified or fractionated from the source of origin. Generally, this requires a large amount of energy and chemicals; therefore, more sustainable processing options need to be designed. Within this thesis, we investigate electrochemical separation processes for ions and proteins. These processes bear great potential to reduce energy and solvent use compared to membrane or chromatographic techniques, since electric energy is directly used without further conversion, and fast and easy switching between e.g. negative and positive surfaces makes it unnecessary to regenerate solid supports with solvents or buffers. Nevertheless, to unfold the full potential of electrochemical separation processes, development of electrodes for selective separation, and the design of the overall process need to be taken to a next level. Both issues are crucial when extending the principles about ion separation to other molecules such as proteins that to date have been hardly explored in this context.

    We first review in Chapter 2 the current state of the art of electrochemical separation processes using capacitive or faradaic principles applied to small ions, proteins, and cells. An important point that is reviewed is the difference between capacitive deionization and inverted capacitive deionization. In the former process, ions are stored capacitively in the electric double layer when a constant electrode potential or current is applied. The release of the ions occurs when releasing the electric bias or by reversing it. In contrast during the latter process, ions are stored due to chemical surface charges and the additional electric potential is only applied during the regeneration phase. Since in this option selective surface coatings may be used, it allows for specifically targeting molecules within a mixture, and still operating without solvents for regeneration. This is a major advantage for protein separation, and thus used in the following chapters, starting from a system with salt that later becomes more complex by the introduction of protein.

    In Chapter 3 and 4 we investigate simple and modified activated carbon electrodes in an inverted capacitive deionization process. We found that ion adsorption at 0 V was possible for simple activated carbon electrodes when used with ion exchange membranes in front of the electrodes (inverted capacitive membrane deionization). We also found a similar separation pattern for electrodes with polyelectrolytes added to the matrix, which in combination with ion exchange membranes resulted in a process that is competitive with conventional capacitive deionization at very low exergy loss. When working with a solution that contains proteins, electrode fouling is a challenge. In Chapter 5 we show that the application of hierarchical carbon electrodes coated with a zwitterionic polymer brush avoids protein adsorption and increases the life time of the electrodes during desalination. However, when proteins need to be separated, they need to interact with the surface of the electrode while still desorbing upon an electric trigger.

    In Chapter 6 we show that activated carbon electrodes containing cationic and anionic polyelectrolytes have the ability to reversibly adsorb and release protein by applying an electric potential bias. While proteins were adsorbed, salt was desorbed and vice versa, therewith also showing a potential for desalting protein solutions. In Chapter 7 we investigated the forces acting on salt and proteins in detail, and measured an increase in electric and hydration repulsion at the electrode interface due to an externally applied electric potential which influenced surface wetting. Overall, we concluded that the changes induced by the electric potential were sufficient to influence protein ad- and desorption. Since in Chapter 7 the measurements were conducted on gold substrates, we presented in Chapter 8 as a first step toward carbon based electrodes reduced graphene oxide coated silicon substrates to study protein ad- and desorption.

    The findings described in this thesis are important for the development of novel electrochemical separation processes for complex molecules, and they lay the ground work for a next generation of sustainable separation technologies. Thus, in Chapter 9 our findings were put into perspective, and we highlighted research required to further design electrochemical separation processes. We indicated that suitable (responsive) surface coatings, and optimized process designs for large scale applications are key to unlock the full potential of electrochemical separation processes and to guarantee their successful implementation.

    The effect of deacetylation on chitin nanocrystals for the production of chitin-PLA nanocomposites
    Boer, Kieke de; Colijn, Ivanna ; Schroen, C.G.P.H. - \ 2019
    The replacement of traditionally used fossil fuel based plastics with bioplastics would contribute to the transition to a more sustainable circular economy Unfortunately, bioplastics often do not meet requirements in terms of strength and barrier properties and are therefore unsuited to function as food packaging material In this research, we aim at improving properties of a promising bioplastic, polylactic acid ( by the incorporation of chitin nanocrystals. The major focus lays on the effect of deacetylation on the properties of the chitin nanocrystals During deacetylation, acetylgroups on the chitin nanocrystals are replaced by amino groups
    Application of microfluidics in the production and analysis of food foams
    Deng, Boxin ; Ruiter, Jolet De; Schroën, Karin - \ 2019
    Foods — Open Access Food Science Journal 8 (2019)10. - ISSN 2304-8158
    Coalescence - Dynamic surface tension - Emulsions - Foams - Microfluidics - Monodispersity - Up-scaling

    Emulsifiers play a key role in the stabilization of foam bubbles. In food foams, biopolymers such as proteins are contributing to long-term stability through several effects such as increasing bulk viscosity and the formation of viscoelastic interfaces. Recent studies have identified promising new stabilizers for (food) foams and emulsions, for instance biological particles derived from water-soluble or water-insoluble proteins, (modified) starch as well as chitin. Microfluidic platforms could provide a valuable tool to study foam formation on the single-bubble level, yielding mechanistic insights into the formation and stabilization (as well as destabilization) of foams stabilized by these new stabilizers. Yet, the recent developments in microfluidic technology have mainly focused on emulsions rather than foams. Microfluidic devices have been up-scaled (to some extent) for large-scale emulsion production, and also designed as investigative tools to monitor interfaces at the (sub)millisecond time scale. In this review, we summarize the current state of the art in droplet microfluidics (and, where available, bubble microfluidics), and provide a perspective on the applications for (food) foams. Microfluidic investigations into foam formation and stability are expected to aid in optimization of stabilizer selection and production conditions for food foams, as well as provide a platform for (large-scale) production of monodisperse foams.

    Batch stripping of flavour active compounds from beer: Effect of dry matter and ethanol on equilibrium and mass transfer in a packed column
    Ammari, Ali ; Schroën, Karin - \ 2019
    Food and Bioproducts Processing 118 (2019). - ISSN 0960-3085 - p. 306 - 317.
    Alcohol - CO - Equilibrium - Ester - Henry's law constant - Mass transfer coefficient

    Physiochemical similarities of volatile compounds and their interactions with the beer matrix are the main challenging factors in selective separation of ethanol for the production of non-alcoholic beer and removal of excess (off-)flavours produced during fermentation, such as isoamyl acetate. In this paper, we are especially interested in the effect of beer dry matter, a complex mixture of carbohydrates and proteins, and of ethanol on flavour behaviour during treatment with a packed bed column using CO2 as a stripping agent. By analysing the gas phase at different dry matter concentrations, we observed that its’ presence is a facilitating factor for ethyl acetate and isoamyl acetate release, whereas isoamyl alcohol is retained in the liquid phase. These effects are a result of combined mass transfer effects and affinity for carbon dioxide, which are both affected by the presence of ethanol in the feed stream. Mass transfer analysis of isoamyl alcohol and ethanol revealed that the resistance is not controlled by their solubility in water but the affinity to CO2.

    Lipid oxidation in emulsions fortified with iron-loaded alginate beads
    Cengiz, Alime ; Schroën, Karin ; Berton-Carabin, Claire - \ 2019
    Foods — Open Access Food Science Journal 8 (2019)9. - ISSN 2304-8158
    Alginate beads - Ferrous sulfate - Ionic gelation - Iron encapsulation - Iron fortification - Lipid oxidation - O/W emulsion

    The potential use of iron-loaded alginate beads to fortify oil-in-water (O/W) emulsions was studied. Iron-loaded alginate beads with different sizes (0.65, 0.84, 1.5 and 2 mm) were produced by ionic gelation with calcium chloride, leading to 81% encapsulation efficiency (EE) of ferrous sulfate. These beads were added to O/W emulsions to investigate their effect on lipid oxidation. The use of iron-loaded alginate beads inhibited lipid oxidation in emulsions, compared to a control emulsion with the same concentration of free ferrous sulfate in the continuous phase, but did not totally prevent it. Results obtained with scanning electron microscopy and energy dispersive X-ray spectroscopy (EDX) analysis showed that some reactive iron was present at the surface of the beads. Oxidation of the lipid droplets was slightly higher for smaller alginate beads, suggesting that the reaction could be linked to the total bead surface. When covering iron-loaded beads with an extra layer of alginate, lipid oxidation was inhibited, which confirmed the role of reactive surface-bound iron. This study shows that the location of iron within the encapsulates plays a crucial role in the chemical stability of fortified foods and should be taken as a starting point in the design of iron-fortified food products.

    Effect of Ethanol and Temperature on Partition Coefficients of Ethyl Acetate, Isoamyl Acetate, and Isoamyl Alcohol: Instrumental and Predictive Investigation
    Ammari, Ali ; Schroen, Karin - \ 2019
    Journal of Chemical and Engineering Data 64 (2019)8. - ISSN 0021-9568 - p. 3224 - 3230.

    For alcoholic beverages such as beer, downstream processing for either dealcoholization or off-flavor removal requires both quantitative data and suitable predictive methods. Along with experimental investigations, we use a method initially developed for studying the solubility of gases in two or more miscible liquid solvents to monitor the effect of ethanol on air-water partition coefficients of three major flavors found in beer, namely, isoamyl alcohol, ethyl acetate, and isoamyl acetate. In the ethanol concentration range between 0 and 0.1 mole fraction, a slight, rather linear increase in the Henry's solubility coefficient was observed. This overall behavior can be captured well using Henry coefficients for aqueous binary and ternary systems together with the Wohl expansion for excess Gibbs free energy coupled with the one-parameter Margules equation. Based on the developed model, the Wohl's expansion parameter for ethanol-water is introduced as the solvent-solvent interaction parameter. The van 't Hoff parameters for temperature dependence of Henry coefficients for binary water-flavor solutions are determined in the range of 30 to 60 °C.

    Synergistic stabilisation of emulsions by blends of dairy and soluble pea proteins: Contribution of the interfacial composition
    Hinderink, E.B.A. ; Münch, Katharina ; Sagis, L.M.C. ; Schroen, C.G.P.H. ; Berton-Carabin, C.C. - \ 2019
    Food Hydrocolloids 97 (2019). - ISSN 0268-005X - 11 p.
    Interfacial displacement - SDS-PAGE - Emulsion stability - Dairy proteins - Plant proteins - Protein mixtures
    Proteins from animal and plant sources are known to be able to physically stabilise emulsions, whereas much less is known about emulsions prepared with blends of proteins of different origin. Here we use blends of pea protein isolate (PPI) with whey protein isolate (WPI) or with sodium caseinate (SC) to physically stabilise emulsions prepared by high pressure homogenisation. For both the blends and the individual proteins, droplet size, emulsion stability, surface load and interfacial compositions were determined. The d3,2 and surface load (measured over a concentration range 0.2–1.6 wt% protein in the starting aqueous solution) were the lowest for SC- and WPI-stabilised emulsions, and the highest for PPI-stabilised emulsions, whereas emulsions stabilised by the blends (1:1 ratio) had intermediate d3,2 values and surface loads. PPI- and SC-stabilised emulsions showed some physical destabilisation (e.g., flocculation and coalescence, respectively) over 14 days of storage, whereas the WPI-PPI or SC-PPI blends formed emulsions that remained stable, suggesting synergistic effects.When used in blends, both dairy and plant proteins adsorbed at the oil-water interface, but compositional rearrangements at the interface occurred within days. More specifically, whey proteins were able to partly displace pea proteins from the interface, which were themselves able to displace SC. However, such a displacement was only possible when the displacing protein was present in sufficiently high excess. Such considerations are usually not taken into account in food emulsion formulation, even though they are very relevant, as the interfacial layer protects emulsions droplets against physical destabilisation.
    Towards new food emulsions: designing the interface and beyond
    Berton-Carabin, Claire ; Schroën, Karin - \ 2019
    Current Opinion in Food Science 27 (2019). - ISSN 2214-7993 - p. 74 - 81.

    Emulsions are ubiquitous in foods, and decades of research work have led to advanced, although often empirical, control over the formulation and functionality of those systems. However, the conventional strategies to make food emulsions have to be revisited, due to the trends in the food sector area that have emerged in recent years. This includes a strong focus on naturalness, health and sustainability, which promotes the use of plant-derived ingredients, ideally obtained from mild processing, and thus, by essence, far from pure and well-characterized. Adapting to this change of mind while ensuring the physicochemical stability of emulsions is a challenge, and requires that researchers invest effort into deep characterization of the emulsions’ microstructure and dynamics, for which tools to characterize multiple scales are, more than ever, an essential need.

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