The thermal degradation of ascorbic acid (AA) in orange juice was analysed over in a 20–45 °C temperature range. Dehydroascorbic acid (DA), pH and browning were also monitored. Small amounts of AA degradation could be described by first order kinetics, but when only low amounts of AA were retained sigmoidal kinetics were clearly appropriate. The Weibull model was used to describe this pattern (R2adj > 0.995). The rate constant increased with temperature according to an Arrhenius‐type relationship. The activation energy was 38.6 kJ/mol and at the average temperature of the range tested, 32.5 °C, the rate constant was 64.4 × 10−3 h−1. The shape constant decreased linearly with temperature, from 2.17 to 1.13. Before the time when the maximum degradation rate occurred, pH, DA concentration and browning remained fairly constant, and then increased. It was found that this behaviour, as well as the dependence of the shape constant on temperature, might be explained by (i) the reconversion of DA into AA, following first order kinetics in relation to DA and second order kinetics in relation to AA, and by (ii) different sensitivities of the reaction rate constants to temperature. Browning was also well described by the Weibull model with a temperature independent shape constant.
The kinetics of water loss in the apple cultivar Golden during osmotic dehydration in sucrose solutions was studied. Two sets of experiments were performed, each following a full factorial design at five levels for sucrose concentration (0.45–0.65 w/w) and temperature (20–40 °C). The first set was designed to assess the adequacy of the Weibull model to describe water losses, whereas the second set was designed to improve parameter estimation, based on the D‐optimal design concept. The model provided good fits to the experimental data, and the
D‐optimal design yielded improved parameter precision. The shape parameter of the model was 0.5 and statistically independent of both temperature and sucrose concentration. The rate constant ranged between 0.004 and 0.012 min−1 and increased with temperature following an Arrhenius type relationship, with the activation energy increasing linearly with concentration. The interactive effects of temperature and sucrose concentration on the process kinetics were analysed.
: The quality evaluation of mushrooms was studied by storing fresh white button mushrooms (Agaricus bisporus) for 6 to 8 d, at various controlled temperature conditions (3.5 to 15 °C) and measuring the instrumental textural hardness and color of the mushroom cap for different product batches. A nonlinear mixed effect Weibull model was used to describe mushroom cap texture and color kinetics during storage considering the batch variability into account. Storage temperature was found to play a significant role in controlling texture and color degradation. On lowering storage temperature (i) the extent of the final browning extent in the mushroom after storage was reduced and (ii) the rate textural hardness losses was slowed down. A linear dependence of the final browning index with temperature was found. An Arrhenius type relationship was found to exist between the temperature of storage and storage time with respect to textural hardness. The average batch energy of activation was calculated to be 207 ± 42kJ/mol in a temperature range of 3.5 to 20 °C.
Practical Application: This article evaluates how temperature abuse affects mushroom texture and color, applying methods that allow for the consideration of the natural product variability that is inherent in mushrooms. Its results apply to mushroom producers, retail distribution, and supermarkets for effective storage management.
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