Major loses were seen in GSH contents of thermal dried tomato and gingersamples (Table 1).
Cys content of the samples also showed significant
differences between the freeze dried and thermal dried
samples. Also, Cys content of tomatoes did not changed significantly
by freeze drying. The losses seen in the GSH and Cys contents
after using the thermal drying method may have been the
result of accelerated degradation due to heat and oxygen. Freeze
drying was achieved under vacuum at a low temperature. Besides,
the freeze drying method, provided highly efficient extraction. The
reason for this could originate from the ice crystals in the plant
extract matrix damaged cellular structures, thereby causing intracellular
components of the cells to reach the solvent to help provide
better extraction (Asami, Hong, Barrett, & Mitchell, 2003).
Our results are in agreement with previous studies. The samples
from the FD method had more GSH loss than Cys loss, because
the cellular GSH synthesis was limited due to the availability of
Cys. In addition, GSH, a substrate for oxidative enzymes and nonenzymatic
reductant for free radicals and peroxides, is a very active
antioxidant (Kleinman & Richie, 2000; Sen & Packer, 2000).