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ABSTRACT: The feeding mechanism of the sessile protozoon Opercularia asymmetrica (Oligohymenophorea, Peritrichia) relies on the cilia beat generating a flow field that convectively transports suspended particles and dissolved substances to the oral cavity of the organism. By use of optical micro-flow measurement and theoretical methods the flow environment of two neighbouring peritrichous ciliate cells is studied. Both, yeast cells (Saccharomyces cerevisiae) and artificial flow tracers are used for the visualisation of the flow field. Artificial tracers are rejected by the protozoa and deviate from the fluid path lines, while yeast cells follow the flow almost perfectly. This is shown through a dimensional analysis of the involved hydrodynamic forces on the tracers. The measured flow field exhibits maximum velocities of 25 microm/s at around 20 microm distance ahead of an individual ciliate. The flow field extends 200 microm from the location of the ciliate. A nicking motion of the protozoon is observed and found not to obey any periodic law. Multiples of protozoa exhibit most commonly an alternating cilia beat regime generating a non-stationary flow field. It can be shown through theoretical methods that fluid exchange is enhanced in this alternating regime compared to a flow field generated by a single ciliate. Fluid exchange depends on the distance of the ciliates from each other and on the alteration frequency of the cilia beat. The comparison of an analytical Stokes' flow solution with the observed fluid flow serves to determine the force required to maintain the flow field against viscous dissipation. The force magnitude is in the order of magnitude of 10-100 pN.
Journal of Biomechanics 02/2007; 40(1):137-48. · 2.43 Impact Factor
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ABSTRACT: The objective of this work is to gain more insight into the processes of oral perception of food texture. Particularly, the limits for detectable thickness differences of objects, which are evaluated in the human mouth, are investigated. In a sensory study small, flexible circular disks (diameter in mm range) of varying thickness (in microm range) and material properties are evaluated between tongue and palate in human subjects. The thicker sample is identified in pair comparison tests. Experimental evidence suggests the existence of one detection process (attempt to align tongue and palate and the disk between them) to which the tongue-palate system reacts in two different ways: (1) by bending the disk (thickness below 125 microm, Young's modulus of 480 MPa) and (2) by impressing the disk into the tongue (thickness above approximately 200 microm, Young's modulus of 480 MPa), whereas the first reaction is necessarily followed by the second if the first one fails. For both ranges, differences in thickness of 25 microm can be detected. The two reaction processes cover isolated ranges and leave an insecure detection range in between them, for which neither one of the processes applies. Since deformation and load distribution on the disk are supposed to play a major role in the first detection process (the loads exerted on the disk in order to bend it are compared), we formulate a mathematical model to quantify these mechanical effects. The model is employed to identify parameter constellations (thickness, material properties) for which the insecure range is omitted or the range is enlarged. Theoretical findings are confirmed by further experiments. Their results are consistent with the characteristics and functioning of the mechanoreceptors in-mouth.
Journal of Biomechanics 02/2007; 40(16):3533-40. · 2.43 Impact Factor
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ABSTRACT: The heat inactivation of Lactococcus lactis was studied by determination of cell counts, and by FT-IR spectroscopy recording the average structure of cell proteins. Cell counts were measured after incubation milk buffer or milk buffer with 1. 5 M sucrose, and FT-IR spectra were recorded in (2)H(2)O or (2)H(2)O with 1. 5 M sucrose in the range of 6-75 degrees Celsius. Sucrose protected L. lactis against heat inactivation. The cell counts differed by up to 6-log cycles after treatment in milk buffer as compared to milk buffer with sucrose. The (1)H/(2)H exchange in proteins, and secondary structure elements were detected by the analysis of amide I', amide II and amide II' bands. A reduced (1)H/(2)H exchange as well as a lower content of disordered structural elements was observed when sucrose was present. Conformational fluctuations of native proteins as indicated by the (1)H/(2)H exchange were apparent already at sublethal temperatures. The loss of viability of L. lactis occurred in the same temperature range as the loss of the protein secondary structure. These results demonstrate that sucrose protects L. lactis against heat inactivation, and that the increased heat stability of proteins in the presence of sucrose contributed to this enhanced heat resistance.
Biochimica et Biophysica Acta 08/2006; 1764(7):1188-97. · 4.66 Impact Factor
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ABSTRACT: During the compression phase of high pressure treatment of aqueous food, the temperature locally increases approx. 2-3 K per 100 MPa in the isentropic case as a result of the external work done by the volume change of the fluid. It could be concluded in the authors' previous contributions that heat transfer induces undesired process non-uniformities, and therefore, significantly influences the product quality. However, the turbulent inflow conditions existing in larger autoclaves are expected to change homogeneity of the thermofluiddynamical fluid. In this contribution, the presence of the turbulence generated during the compression phase of the High -Pressure-treatment and its influence on process non-uniformities throughout the high pressure processing are investigated numerically. For the numerical simulations, a three-dimensional model of a cylindrical autoclave with a net volume of 3.3 Litre is created. To investigate the influence of the turbulence on product quality, a model of the inactivation of the enzyme Bacillus Subtilis -Amylase is employed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
PAMM 12/2005; 5(1):573 - 574.
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Simulation Modelling Practice and Theory. 01/2005; 13:109-118.
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ABSTRACT: The mechanical effects of the compression of a yeast cell (Saccharomyces cerevisiae) under high hydrostatic pressure (HHP) are modeled and simulated numerically. The deformation of the cell under pressure deviates strongly from isotropic volume reduction. In the cell wall, von-Mises stress reaches the critical value upon failure at a pressure load between 415Mpa and 460MPa. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
PAMM 11/2004; 4(1):316 - 317.
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ABSTRACT: The mechanical effects of the compression of a yeast cell (Saccharomyces cerevisiae) under high hydrostatic pressure used for the processing of food and food ingredients are modelled and simulated with the finite-element method. The cell model consists of a cell wall, cytoplasm a lipid filled vacuole and the nucleus. Material parameters have been taken from literature or have been derived from thermodynamic relationships of water and lipids under high hydrostatic pressure. The model has been validated for a pressure load up to 250 MPa. Comparison of the volume reduction to in situ experimental observations reveals very good agreement. Dimensional analysis of the governing equations shows that transient pressure application in a high-pressure food process does not enhance structural inactivation (mechanical damage), unless pressure oscillation frequencies of 700 MHz are applied. The deformation of the cell under pressure deviates strongly from isotropic volume reduction. Especially, organelle membranes exhibit large effective strain values. Hydrostatic stress conditions are preserved in the interior part of the cell. A pressure load of 400 MPa, which is critical upon disruption of cell organelle membranes, generates an effective strain up to 80%. In the cell wall, the stress state is heterogeneous. Von-Mises stress reaches the critical value upon failure of the cell wall of 70+/-4 MPa at a pressure load between 415 and 460 MPa.
Journal of Biomechanics 08/2004; 37(7):977-87. · 2.43 Impact Factor
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ABSTRACT: This numerical study evaluates the momentum and mass transfer in an immobilized enzyme reactor. The simulation is based on the solution of the three-dimensional Navier-Stokes equation and a scalar transport equation with a sink term for the transport and the conversion of substrate to product. The reactor consists of a container filled with 20 spherical enzyme carriers. Each of these carriers is covered with an active enzyme layer where the conversion takes place. To account for the biochemical activity, the sink term in the scalar transport equation is represented by a standard Michaelis-Menten approach. The simulation gives detailed information of the local substrate and product concentrations with respect to external and internal transport limitations. A major focus is set on the influence of the substrate transport velocity on the catalytic process. For reactor performance analysis the overall and the local transport processes are described by a complete set of dimensionless variables. The interaction between substrate concentration, velocity, and efficiency of the process can be studied with the help of these variables. The effect of different substrate inflow concentrations on the process can be seen in relation to velocity variations. The flow field characterization of the system makes it possible to understand fluid mechanical properties and its importance to transport processes. The distribution of fluid motion through the void volume has different properties in different parts of the reactor. This phenomenon has strong effects on the arrangement of significantly different mass transport areas as well as on process effectiveness. With the given data it is also possible to detect zones of high, low, and latent enzymatic activity and to determine whether the conversion is limited due to mass transfer or reaction resistances.
Biotechnology and Bioengineering 10/2003; 83(7):780-9. · 3.95 Impact Factor
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Computational Science - ICCS 2002, International Conference, Amsterdam, The Netherlands, April 21-24, 2002. Proceedings, Part I; 01/2002
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ABSTRACT: Perception of sour, sweet, bitter, and salty taste can be related to specialized sensors (taste buds), however, this is not possible for texture perception. Although different types of oral mechanoreceptors are known, it remains unclear how texture perception relates to these structures. The aim of this work is to better understand textural attributes such as grittiness. As a first step to this end, an experimental determination of size resolution capability was carried out. Small discs of varying diameter, thickness, and materials were evaluated by subjects for differences in diameter and thickness between tongue and palate (oral system) and also between finger and palm (manual system). Diameter determination was found to be very accurate. Thickness evaluation was more complex and appeared to rely on two mechanisms. Differences between the manual and oral evaluation were found and could be explained in terms of mechanical models as well as anatomical data. The hypothesis of two different mechanisms was experimentally verified.
Food Quality and Preference.
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ABSTRACT: This paper describes the development of a new method to detect damages on crates of beverages. Therefore, a pattern-recognition-system based on an artificial neural network (ANN) is applied on frequency spectra obtained by mechanical vibration response analysis. To support the network training a large number of numerical data-sets is calculated by finite-element-method (FEM). The combination of artificial neural networks with methods of numerical simulation is a powerful instrument to cover the broad ranges of possible damages. First results are presented and discussed.
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ABSTRACT: Thermofluiddynamics and process uniformity of high-pressure processing in a laboratory-scale autoclave (3.3 l volume) is assessed by use of experimental and numerical simulation techniques. Direct treatment of water at pressure levels of 500 and 300 MPa and with a pressure holding phase of 820 s is considered. Multiple thermocouple measurements are in excellent agreement with numerically simulated temperature fields. Thus, it can be shown that the temperature level in the chamber is only roughly influenced by a tempering device due to thermal inertia of the solid structure of the chamber (initial configuration). In case of a high-pressure-induced enzyme inactivation, it is shown that thermal insulation of the internal wall allows a reduction of process cycle duration by 40% with respect to the initial configuration. This is valid also for highly viscous liquids, which, in turn, exhibit strong non-uniformities.
Innovative Food Science & Emerging Technologies 5(4):399-411. · 3.03 Impact Factor
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ABSTRACT: Recognition of representative damages on returnable crates of beverages is carried out by an artificial neural network (ANN) trained exclusively with frequency response spectra from finite-element simulations. Finite-element mode shape analysis implies that two sensors are sufficient for successful damage recognition. Amongst three topologies, a loose coupling of two ANN yields best recognition results, each processing data from one sensor. Out of 91 experimental recordings 65 of 66 data sets representing twenty damage types are recognised. The classification fails for some data sets of intact crates, due to experimental conditions not accounted for in the finite-element simulation.
Computer Methods in Applied Mechanics and Engineering.
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ABSTRACT: A mathematical model to predict lethal and sublethal pressure effects on Lactococcus lactic was established through combined use of Principal Component Analysis (PCA) and Fuzzy Logic. The model was based on data comprising pressure inactivation kinetics with 64 combinations of the parameters pressure, temperature, pH, and buffer composition, samples were analysed with respect to 5 physiological states describing lethal or sublethal injury of L. lactis, i.e. viable cell counts (CFU), undamaged cell counts (CFUsub), membrane integrity (MI), metabolic activity (MA) and the activity of the membrane bound enzyme LmrP (LmrP).Correlations found by PCA were used to generate a bi-layer fuzzy model using clustering methods and rule oriented statistical analysis as well as the physiological states CFU and LmrP as autonomous output variables. The result of these variables is used to accurately predict dependent output variables MA, CFUsub, and MI taking into account the combined effects of the inactivation process.Industrial relevanceThe study provides a predictive model for the inactivation of an industrially relevant micro-organism. Predictive models are useful for process design on the industrial scale. Further, our model provides information about intermediate steps of high pressure inactivation.
Innovative Food Science & Emerging Technologies.
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ABSTRACT: Mechanical stresses and deformation of cellular structures due to the application of high hydrostatic pressure (HHP) is analysed for two cases. In the first case, a liquid-filled spherical shell with linear elastic material properties is considered as first approximation of a biological cell. The theoretical analysis reveals the existence of severe non-hydrostatic mechanical stresses in the wall of the structure.As second case, a nonlinear model of a yeast cell (Saccharomyces cerevisiae) under high hydrostatic pressure is assessed by use of the finite-element method. It is observed that hydrostatic stress conditions are preserved in the interior part of the cell, while non-hydrostatic stress is encountered in the cell wall. There, von-Mises stress reaches its critical value upon failure (70 ± 4 MPa) at a pressure load between 415 MPa and 460 MPa. This confirms observations of cell wall damage at this pressure as reported earlier by other authors.Industry Relevance of the Content of Manuscript 042405344The current manuscript considers mechanical stresses included in biological cellular structures when exposed to high hydrostatic pressure. It reveals that current idea about the existence of a hydrostatic stress state in any structure under hydrostatic pressure is incorrect.By use of a linear analytical model and a nonlinear numerical model, it can be shown that heterogeneous mechanical stresses occur in solid bodies as long as latter consist of materials with different mechanical properties.Since this result can be generalised to biological and non-biological macroscopic mechanical structures, the paper is, to some extent, relevant for industrial applications. For example, food packages such as bottles, cans and soft pouches represent such structures consisting of different materials. They might be exposed to heterogeneous mechanical stress leading to damage during high-pressure processing.The authors intend to do research on mechanical stresses in natural and industrial food packages during high-pressure treatment in the future.
Innovative Food Science & Emerging Technologies.
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ABSTRACT: Subject of the present contribution is the numerical simulation of the effect of a elongational flow field on a suspended particle-aggregate. The particle-aggregate consists of seven rigid spherical particles and is suspended in the flow field at low Re-numbers (Re=0.01–0.1). The ratio of particle and fluid densities varies between 1 and 15. The velocity and pressure distribution is obtained from the numerical solution of the Navier–Stokes equation and the continuity equation based on finite volume methods. The particle motion is obtained from the Euler equation of motion for rigid bodies. A comparison of classical solutions with the result of the numerical simulation for a spherical particle shows a very good agreement. It can be shown, that the interaction of the aggregate with the fluid differs clearly from that of a spherical particle. Furthermore, it has been found that the magnitude of stresses on the aggregate surface is increasing with time monotonously. Shear stress is maximum on the outer parts of the aggregate. Normal stress takes on maximum values on the upstream and downstream oriented faces. The maximum pressure drop across the particle results in an extensional force which increases in time within the considered period.
European Journal of Mechanics - B/Fluids.
