In this work,
This increase is
related to the formation of phenolic compounds usually associated
to availability of precursors of phenolic molecules arising
from non-enzymatic inter-conversion between the phenolic
molecules [8]. Similarly, TPC increased from 9.6 mg GAE/
100 g d.m. in fresh sage to over 30.0 mg GAE/100 g d.m.
during air drying at room temperature, while TPC in thyme
changed from 20.0 to 112.0 mg GAE/100 g d.m. during similar
drying operation. Drying of Stevia leaves at temperatures
higher or equal to 60 °C caused on the contrary a slight decrease
in TPC and TFC. Drying at 80 °C reduced TPC to
21.11 ± 1.02 mg GAE/100 g d.m. equivalent to 73 % of the
original value, while TFC is reduced to 71.87 ± 1.33 mg QE/
100 g d.m, equivalent to only 81 % of the initial value, which
meant that under the controlled air drying conditions drastic
losses of antioxidant compounds did not occur. On the contrary,
low temperature drying below 50 °C would increase
TPC and TFC in the dried products. According to Mrad et
al. [9], a decrease in TPC during drying may be attributed to