According to Mrad et
al. [9], a decrease in TPC during drying may be attributed the binding of polyphenols with other compounds such as
proteins, or to alterations in the chemical structure of polyphenols
that cannot be extracted nor determined by available
methods. In contrast to the results reported in this work,
Periche et al. [10] reported an increase in TPC and TFC of
dried Stevia leaves. During convective drying at 180 °C for
3 min TPC increased from 44.40 ± 1.04 mg GAE/g d.m. in the
fresh Stevia leaves to 76.8 mg GAE/g d.m. in the dried leaves,
while TFC increased from 2.52 ± 0.24 to 45.1 mg catechin
equivalent/g d.m. Drying at 100 °C for 3 min showed on the
other hand a decrease in TPC to 31.5 mg GAE/g d.m., but an
increase in TFC to 17.2 mg catechin equivalent/g d.m. During
shade drying for 30 days at 20 °C TPC decreased slightly to
39.1 mg GAE/g d.m., while TFC increased to 20.3 mg catechin
equivalent/g d.m. A comparison with the results of this
study would indicate the concurrent effects of temperature and
drying time on the biochemical changes occurring during the
drying process.