3. Results and discussion
First, simulation results at constant temperature are compared
with optimized temperature trajectories. Then, the simulations are
validated using two sets of drying experiments for broccoli drying:
1) at constant temperature, and 2) with optimized temperature
trajectories.
3.1. Simulation at constant temperature
Simulation results for the degradation of Vc, GR and MYR during
drying at 40 C and 50 C are given in Fig. 2. The time window for
the simulations was the time needed to achieve a final moisture
content of 0.1 kg water kg dry matter1 and depends on the
applied drying strategy. GR is the most stable compound compared
to MYR and Vc. Retention of GR is over 70% after 24 h of drying at
50 C.
Vc degradation for both models from Table 1 is simulated. The
Vc degradation rate for the model given by Mishkin, Saguy, and
Karel (1984) is higher than the earlier presented model by
Mishkin et al. (1983). Both models have the highest, but a different,
Vc degradation rate in the moisture content range between 0.5 and
1 kg water kg dry matter1 (Fig. 1).
MYR is most heat sensitive compared to GR and Vc. With the
high inactivation rate constant the inactivation of MYR occurred in
a short time. After 3e4 h there is hardly any activity left.
The simulated product temperature trajectory for the inlet air
temperature of 40 and 50 C is given in the state diagram (Fig. 3).
The diagram shows how the product degrades by passing the heat
sensitive areas.
3.2. Optimized drying trajectories
The optimal product temperature trajectory is given in Fig. 3.
The simulated degradation of Vc, GR and MYR is also presented in