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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    Interfacial rheology and relaxation behavior of adsorption layers of the triterpenoid saponin Escin
    Giménez-Ribes, Gerard ; Habibi, Mehdi ; Sagis, Leonard M.C. - \ 2020
    Journal of Colloid and Interface Science 563 (2020). - ISSN 0021-9797 - p. 281 - 290.
    Dilatational - Escin - Interfacial rheology - Non-linear Viscoelastic (NLVE) regime - Relaxation - Saponin - Shear - Stretched exponential

    Hypothesis: Escin, a monodesmosidic triterpenoid saponin, was shown previously to form viscoelastic interfaces with a very high dilatational and surface shear storage modulus. This is expected to be due to the arrangement of Escin into 2D disordered soft viscoelastic solid interfacial structures, which results in turn in a distribution of relaxation times. Experiments: The responses to dilatational and surface shear deformations of Escin-stabilized air-water interfaces were studied, both in the linear viscoelastic (LVE) and non-linear (NLVE) regime. Step relaxation and amplitude sweeps were performed in dilatation experiments. For surface shear, amplitude sweeps and creep recovery experiments were performed. Findings: Escin stabilized-interfaces displayed a highly non-linear behavior in dilatation as seen in the Lissajous plots. In large oscillatory shear the Lissajous curves had a rhomboidal shape, indicating intracycle yielding and recovery, typical of glassy systems. The relaxation of the interface showed stretched exponential behavior, with stretched exponents typical of disordered solids with dynamic heterogeneity. The use of surface rheological measurements beyond the commonly measured LVE regime clearly has provided new insights into the behavior of these interfaces and their microstructure. These results highlight the need to reconsider other complex interfaces as disordered solids and not as 2D homogenous viscoelastic fluids.

    Shear-induced structuring as a tool to make anisotropic materials using soy protein concentrate
    Grabowska, Katarzyna J. ; Zhu, Sicong ; Dekkers, Birgit L. ; Ruijter, Norbert C.A. de; Gieteling, Jarno ; Goot, Atze J. van der - \ 2016
    Journal of Food Engineering 188 (2016). - ISSN 0260-8774 - p. 77 - 86.
    Fibrous structure - Shear - Shearing equipment - Soy protein concentrate

    This research presents the formation of anisotropic, and partly fibrous, semi-solid structures with Soy Protein Concentrate (SPC) using the concept of shear-induced structuring. The morphological and mechanical properties of the structures obtained are analyzed using confocal scanning laser microscopy (CSLM), and large scale mechanical deformation analysis. We present process conditions leading to the formation of anisotropic structures in SPC and found that comparable conditions did not result in anisotropy when using soy protein isolate. Results indicate the importance of the dry matter content, the process temperature and the presence of carbohydrates in structure formation. CSLM pictures show that carbohydrates form a separate phase in the system, which is oriented upon processing. The need for high temperatures also required the development of next generation shearing equipment.

    Surface properties of adsorption layers formed from triterpenoid and steroid saponins
    Pagureva, N. ; Tcholakova, S. ; Golemanov, K. ; Denkov, N. ; Pelan, E. ; Stoyanov, S.D. - \ 2016
    Colloids and Surfaces. A: Physicochemical and Engineering Aspects 491 (2016). - ISSN 0927-7757 - p. 18 - 28.
    Air-water interface - Dilatation - Saponins - Shear - Surface rheology

    Saponins are natural surfactants with non-trivial surface and aggregation properties which find numerous important applications in several areas (food, pharma, cosmetic and others). In the current paper we study the surface properties of ten saponin extracts, having different molecular structure with respect to the type of their hydrophobic fragment (triterpenoid or steroid aglycone) and the number of sugar chains (1 to 3). We found that the triterpenoid saponins Escin, Tea Saponin and Ginsenosides have area per molecule in the range between 0.5 and 0.7nm2, and the adsorbed molecules are orientated perpendicularly to the interface. The comparison of the experimentally measured surface elasticities with theoretically estimated ones shows that the saponins with very high dilatational and shear elasticities (up to 2000mN/m) have molecular interaction parameter in the adsorption layers which is above the threshold value for two-dimensional phase transition. In other words, the highly elastic layers are in surface condensed state, due to strong attraction between the adsorbed molecules. Furthermore, these adsorption layers have non-linear rheological response upon expansion and contraction, even at relatively small deformation. Layers from the other studied saponins (steroids and crude mixtures of triterpenoid saponins), which are unable to form strong intermolecular bonds within the adsorption layer, have zero shear elasticity and viscosity and low dilatational elasticity and viscosity, comparable in magnitude to those reported in literature for protein adsorption layers. The comparison of the results, obtained by several independent experimental methods, allowed us to formulate the conditions under which the results from different interfacial rheology tests could be compared, despite the complex non-linear response of the saponin adsorption layers.

    On the use of the Couette Cell technology for large scale production of textured soy-based meat replacers
    Krintiras, Georgios A. ; Gadea Diaz, Javier ; Goot, Atze Jan Van Der; Stankiewicz, Andrzej I. ; Stefanidis, Georgios D. - \ 2016
    Journal of Food Engineering 169 (2016). - ISSN 0260-8774 - p. 205 - 213.
    Fibrous structure - Gluten - Meat replacer - Plant protein - Shear - Soy

    We have demonstrated that application of simple shear flow and heat in a Couette Cell is a scalable process concept that can induce fibrous structural patterns to a granular mixture of plant proteins at mild process conditions. In particular, a Couette Cell device with 7-L capacity was employed for the production of structured soy-based meat replacers. A reduced factorial experimental design was used to find the optimum process conditions between two relevant process parameters (process time and rotation rate), while the process temperature remained constant at 120 °C. Fibre-structured products with high anisotropy indices were produced. Fibrousness is favoured at 30 ± 5 min and 25 ± 5 RPM. The up-scaled Couette Cell can be operated in higher industrial values and yield 30 mm thick meat replacers, which emulate meat. Besides, the study did not reveal any barriers for further upscaling of this concept. The flexibility in design allows production of meat alternative products with sizes that are currently not available, but could have advantages when aiming at replacement of complete muscular parts of animals, for instance, chicken breast or beef meat.

    The effect of fine bubble aeration intensity onmembrane bioreactor sludge characteristics and fouling
    Temmerman, L. De; Maere, T. ; Temmink, H. ; Zwijnenburg, A. ; Nopens, I. - \ 2015
    Water Research 76 (2015). - ISSN 0043-1354 - p. 99 - 109.
    Floc size dynamics - MBR - Particle size distribution - Shear - Size exclusion chromatography - Submicron particle concentration

    While most membrane bioreactor (MBR) research focuses on improving membrane filtration through air scour, backwashing and chemical cleaning to physically counteract fouling, relatively few studies have dealt with fouling prevention, e.g. minimizing the impact of operational settings that negatively impact sludge filterability. To evaluate the importance of those settings, the effects of bioreactor aeration intensity variations on membrane fouling have been studied in a lab-scale MBR setup while simultaneously monitoring a unique set of key sludge parameters. In particular, this paper focuses on the impact of shear dynamics resulting from fine air bubbles on the activated sludge quality and flocculation state, impacting membrane fouling. When augmenting the fine bubble aeration intensity both the total and irreversible fouling rate increased. Major indications for sludge filterability deterioration were found to be a shift in the particle size distribution (PSD) in the 3-300μm range towards smaller sludge flocs, and increasing concentrations of submicron particles (10-1000nm), soluble microbial products and biopolymers. When lowering the aeration intensity, both the sludge characteristics and fouling either went back to background values or stabilized, respectively indicating a temporary or more permanent effect, with or without time delay. The shift in PSD to smaller flocs and fragments likely increased the total fouling through the formation of a less permeable cake layer, while high concentrations of submicron particles were likely causing increased irreversible fouling through pore blocking. The insights from the performed fouling experiments can be used to optimize system operation with respect to influent dynamics.

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