dried blueberries compared to those obtained by using HACD. Similarly,
Kwok et al. (2004) showed that MWVD berries retained 48–
64% of TPC, while that subjected to HACD retained only 34–43% of
TPC. In the present study, the contents of TPC in berries dried using
HACD at 60 C + MWVD and HACD at 90 C + MWVD were
0.71 ± 0.01 g GAE 100 g1 DM and 1.19 ± 0.03 g GAE 100 g1 DM,
respectively. The results show that due to significantly shorter initial
convective drying, the combination of HACD at 90 C and
MWVD allowed to obtain significantly higher content of TPC than
HACD at 60 C + MWVD (Fig. 3a). Even HACD at 90 C + MWVD
was significantly shorter (42%) than HACD at 90 C, it produced
final products with comparable contents of TPC. Contrary, HACD
at 60 C + MWVD which was significantly shorter (55%) than HACD
at 60 C, produced final product with significantly lower content of
TPC than HACD at the same drying temperature. Most probably,
due to relatively long exposure time to oxygen and high drying
air temperature, polyphenols were significantly reduced during
initial HACD stage. The application of MWVD for previously dried
by HACD blueberries led to the subsequent decline in the content
of TPC. Results indicated that initial HACD at 60 C did not stabilize
the surface of frozen/thawed berries by hardening the outer layer
that resulted in microfissures and leakage of pigmented exudate
during final MWVD. Most likely, freezing/thawing caused signifi-
cant reduction of the thickness of the skin of blueberries