the contents of vitamin C in the fresh and dried
Stevia leaves are also shown, with a significant (p < 0.05) decrease
during the drying process at all temperatures. The content
of vitamin C in dehydrated Stevia leaves decreased from
130.3 ± 3.4 mg/100 g d.m. in the fresh leaves to 74.1 ± 0.4,
60.9 ± 0.7 and 50.1 ± 0.7 mg/100 g d.m. in the leaves dried at
temperatures of 40, 60 and 80 °C, respectively, which meant a
reduction to 57, 47 and 38 % of the initial content for the
respective drying temperatures. At 30 °C, the drymatter content
of the dried Stevia leaves was about 94 % and the content of
vitamin C retained in the leaves was 73.7 ± 1.2 mg/100 g wet
basis. At 80 °C the dry matter content is around 99 % and the
retained content of vitamin C was 49.5 ± 0.5 mg/100 g wet
basis. Therefore, the content of vitamin C found in the dried
Stevia leaves decreased as drying temperature increased, although
it still remained relatively high, which may be considered
a valuable asset for preparation of a naturally sweetened
herbal infusion in tea mixtures or as water-based extracts in
desserts and milk products or directly by the end-user in jams,
stewed fruits, etc. On the other hand, the presence of vitamin C
in the dried leaves may be used as a quality index and also as an
evaluating criterion for thermal treatment. In comparison, in
fresh leaves of peppermint (Mentha piperita) and spearmint
(Mentha spicata), contents of vitamin C of 140 ± 10 and
480 ± 30 μg/kg fresh tissue were found, respectively [25].