Teoretisk studie av kinetiken för aerob C-vitaminförlust under kommersiell värmekonservering och lagring

The non-isothermal aerobic degradation of ascorbic acid (AA), and the formation and subsequent degradation of the dehydroascorbic acid (DHAA) are described by two simultaneous rate equations, assuming that all three underlying reactions follow first or other fixed order kinetics. Also assumed is that the temperature-dependence of these three reactions' rate-constants follows the exponential model, a simpler substitute for the traditional Arrhenius equation. The effective momentary vitamin C's concentration is assumed to be the sum of the AA's and DHAA's momentary concentrations. Plots of the rate equations' numerical solutions for non-isothermal temperature histories, such as those that exist in actual heat preservation processes and commercial storage of foods, allow examining the temperature regime's role in the vitamin C's retention, at least qualitatively, and to evaluate its loss pattern when DHAA is initially absent or already present in the food. The temperature profile can be expressed algebraically or as an interpolating function constructed for digitized data. With the generalized model's version, characterization of the vitamin loss kinetics may require at least nine independent parameters, which ought to be known a priori, assumed on the basis of literature reports or determined experimentally. However, for many practical applications the number of kinetic parameters can be reduced to six. Isothermal loss is a special case, which can be used to test the calculation procedure by comparing the numerical solutions for quasi-isothermal temperature histories with the analytical solutions for truly isothermal temperature profiles. A version of the calculation and simulation procedure has been posted on the Internet as a freely downloadable interactive Wolfram Demonstration, which can be used as a tool to examine the effect of actual and hypothetical temperature histories on the vitamin's retention during heat processing and storage. It can also be used to assess the impact of deviations from the assumed kinetic order and variability in the model's kinetic parameters on the vitamin's retention pattern.