Biochemical changes occurred during drying process with
significant effect of air drying temperature and drying time,
so that the conditions of the drying process should always be
mentioned. The content of vitamin C in the dried Stevia leaves
decreased as drying temperature increased, although it
remained relatively high, which may be considered a valuable
asset in preparation for herbal tea mixtures or water-based
extracts. Drying process between 30 and 50 °C brought a
significant increase in TPC and TFC reaching the highest
value in both cases in leaves dried at 40 °C. Antioxidant activity
measured as ORAC also showed the highest value at
40 °C, indicating a probable favorable drying condition.
Chlorogenic acid, found as the most abundant phenolic acid
in Stevia leaves, was unaffected by drying temperatures.
Sweeteners content was found to increase especially at drying
temperature up to 50 °C, indicating the probable presence of
precursors that are transformed during the drying process.
Mineral content during drying between 30 and 80 °C did not
show a clear tendency to increase or decrease, probably due to
uneven distribution in the Stevia plant tissues.