Franz Werner

Effect of the pressurizing ramp on the inactivation of Listeria innocua considering thermofluiddynamical processes

Abstract The effect of the pressurization ramp on the inactivation kinetics of Listeria innocua suspended in Tris buffer has been studied experimentally in an optical pressure cell. Additionally, the thermofluiddynamical processes occurring at the different pressure ramps have been considered. The results obtained at room temperature show that the inactivation effect of high pressure remains the same in case of a fast pressurization ramp (500 MPa/min) and a slow depressurization ramp (100 MPa/min) in comparison to a slow pressurization ramp (100 MPa/min) and a fast depressurization ramp (500 MPa/min). At the chosen test conditions, the fluiddynamical and thermal processes of the two variations differ only slightly from each other. This has been ascertained by measuring the velocity and temperature distributions occurring at the pressure processes. The conclusion is that the pressurization and depressurization rate, respectively, do not effect per se the inactivation kinetics of Listeria innocua .

Experimental investigation on thermofluiddynamical processes in pressurized substances

In previous investigations it has been shown that thermofluiddynamical processes occur in food related substances at high hydrostatic pressure (HHP) treatment. In order to gain insight into these processes an in-situ measuring technique for visualizing temperature and velocity fields has been developed [1]. Based on extensive test series the thermal and fluiddynamical processes in water have been analyzed. After pressurizing water onto 230 MPa within 12 seconds temperature gradients of 0.1 K/mm are generated in the visible field optical cell. The present study comprises investigations on liquids of higher viscosity. Sucrose solution of 50% (weight percent) has been chosen as model fluid because the viscosity data are available up to 600 MPa [2]. The results show that the temperature gradients are six times higher than those in water under the same test conditions. This in turn may cause heterogeneties of biochemical processes in foods. This correlation has been confirmed by numerical simulations of an enzyme inactivation process [3]. In the present contribution visualized inhomogeneous temperature fields arising in sucrose solution are presented and compared to the thermofluiddynamical processes in water.

Fluiddynamische Untersuchung eines konischen Turbinenrührers

ZusammenfassungIn der vorliegenden Arbeit werden die Ergebnisse einer experimentellen Untersuchung mit Laser-Doppler-Anemometrie an einem konischen Dispergierrührer mitgeteilt. Ziel der Untersuchung war es, den konischen Rührer, der zum Dispergieren eingesetzt werden soll, hinsichtlich seiner fluiddynamischen Eigenschaften zu charakterisieren und mit dem 6-Blatt-Schreibenrührer zu vergleichen. Es hat sich gezeigt, daß der untersuchte Rührer neben einer recht guten Umwälzleistung, die durch den Pumpbeiwert ausgedrückt wird, auch noch über Vorraussetzungen verfügt, die gute Dispergierfähigkeiten erwarten lassen. Dies wird durch Vergleich mit bekannten Ergebnissen für den 6-Blatt-Scheibenrührer belegt. Das Feld der lokalen spezifischen Energiedissipationsraten wurde aus den gemessenen lokalen Schwankungsgeschwindigkeiten u′ (RMS-Wert) berechnet. Die maximalen Energiedissipationsraten sind etwa 12 mal so groß wie der mittlere Leistungseintrag.

Zur Modellierung von Sauterdurchmesser und Hold-up beim Einsatz eines konischen Turbinenrührers zum Dispergieren gas-flüssig

ZusammenfassungIn der vorliegenden Arbeit werden aus dem Vergleich experimenteller Date für den Sauterdurchmesser d32 und den Hold-up ϕ mit Gleichungen aus der Literatur für den verwendeten konischen Turbinenrührer für gas-flüssig Systeme Modellgleichungen für d32 und ϕ angegeben.Die notwendigen Anpassungen der Proportionalitätskonstante in den Literaturgleichungen werden auf der Basis fluiddynamischer Phänomene erläutert. Sie lassen sich durch fluiddynamische Ergebnisse einer früheren Untersuchung mit Laser-Doppler-Anemometrie begründen.Koaleszenzphänomene werden im Modell berücksichtigt, wobei eine Analogie zu Blasensäulen zugrundegelegt wird und sich als tragfähig erwiesen hat. Argumente für die Notwendigkeit der Berücksichtigung der lokalen Fluiddynamik bei der Modellierung von Dispergiervorgängen werden vorgelegt.AbstractBy comparing the experimental data of the Sauter-mean-diameter d32 and the hold up ϕ with models from literature, there are presented equations for d32 and ϕ for the used conical turbine in gas-liquid systems. The necessary adjustment of the proportionality constants of the literature equations will be explained on the basis of fluiddynamical phenomena. It can be established by fluid-dynamical results of a former study carried out with laser-doppler-anemometry.Coalescence phenomena are taken into account in the model using an analogy to bubble columns. The analogy to bubble columns turns out to be suitable. Arguments for the necessity of considering the local fluiddynamics in the modelling of dispersions are presented.

A model for the pressure-viscosity behaviour of aqueous solutions of food ingredients

In the present paper new data on the pressure dependence of the viscosity, of aqueous solutions of sugars and whey protein isolate up to a pressure of 700 MPa are presented and discussed in terms of concentration and temperature. An existing model valid for the concentration dependence of the viscosity at ambient pressure is applied to aqueous sugar solutions. An dimensionless equation describing the dependence of the viscosity of the solution on temperature, concentration and pressure is presented and applied to aqueous solutions of sucrose and glucose. It is shown that for sugar solutions the model is able to predict the pressure dependence of the viscosity of the solution if the behaviour of the solvent is known. The model is also applied to whey protein solutions and pressure induced structural changes are detected. The behaviour of whey protein solutions is compared to sugar solutions under pressure.