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The inactivation kinetics of horseradish peroxidase were determined at several values of pH (3, 4, 7, 9 and 10), temperature (40 to 70 °C) and pressure (7, 8 and 9 kbar). The data were obtained by taking samples from the moment that pressure inside the hydrostatic high pressure vessels reached the value specified, and therefore relate to isothermal and isobaric conditions. The inactivation kinetics were non‐log linear and could be individually well described by the conventional two‐fraction model, but the overall consistency of the kinetic parameters of this model was poor and the model was clearly not robust. Inversely, the kinetic model based on the Weibull probability distribution function yielded good individual fits and also a good overall consistency of the kinetic parameters. The whole set of 327 data points could be well described by an overall model considering that the shape parameter (ß) varied with pressure but not with temperature and that the rate parameter (1/α) varied with temperature according to an Arrhenius law, with a pressure‐independent activation energy, and varied exponentially with pressure. The activation energy and the pressure‐sensitivity parameter did not vary with pH up to pH 9. The results suggested a discontinuity of the kinetic behaviour at pH 10, with a different inactivation mechanism prevailing.
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Adsorption of wine proteins is an essential step in the production of white and rosé wines. In order to develop environmentally friendly adsorption processes, non-swelling adsorbents are required. The performance of selected non-swelling ion-exchange resins (Macro-Prep™ 50S and Streamline® SP) was studied by describing the process kinetics of the adsorption of BSA in a model wine solution. The process was assumed to be diffusion controlled and a shrinking core model was applied. Experiments were performed in the 5–35°C temperature range and with different equilibrium partition coefficients. The results obtained with the shrinking core model were theoretically consistent and the apparent diffusivity values correlated very well with theoretically estimated effective diffusivities combined with a linear dependence of porosity with temperature. Separating the temperature effect on porosity, the apparent diffusivity followed an Arrhenius type dependency with temperature with 16.9 kJ/mole activation energy.
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This paper shows how mathematical concepts can be displayed on World Wide Web pages. A few of the most interesting solutions are outlined although a few others are missing and a few more will be invented very soon. It is for authors to decide which system is the most suitable for their purposes.
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The kinetics of thermal degradation of ascorbic acid was studied in a Maltodextrin matrix at different temperatures between 75 and 140 °C. Isothermal experiments were performed with samples earlier equilibrated in environments of known aw at 4 °C, enclosed in hermetically sealed vials, with water contents (w) between 0.17 and 1.68 g water/g solids. Sampling times were selected according to an optimal experimental design in terms of minimum confidence regions of the parameters estimated, using the Bigelow model and estimates from preliminary experiments. The results showed a quadratic dependence of the reference D-value and linear dependence of the z-value with moisture content: Dr(140 °C) = 150.07 − 290.73w + 269w2 (min); z = 12.14 + 22.99w (°C) and showed the applicability of D-optimal designs for determining kinetic parameters in complex situations, with limited experimental requirements. The dependence of the rate constants with water content could not be described by the WLF model in qualitative terms, although in absolute values this model could be used with constants similar to those expected from glass transition theory. The thermodynamic analysis of the results showed a good application of the compensation theory in the whole range of water contents.
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