The L-ascorbic acid (AC) content of fresh fruitswas 134 mg/100 g
DM (±1). Variation of AC content during cranberry drying at
different temperatures is shown in Table 6. The freeze-drying
caused a decrease in AC. The maximum AC was obtained during
the drying of cranberries at 30 C. With an increase in drying
temperature a decrease in AC was observed (average from 100 to
64 mg/100 g DM for cranberries without AC addition). The whole
dried cranberries were characterized by a lower content of AC in
comparison to dried material obtained from pulped fruits. This is
probably caused by the longer drying time of whole cranberries.
Dried cranberries with the addition of citric acid showed slightly
higher values for AC than dried material without this acid addition.
A similar situationwas observed for dried fruits with the addition of
a mixture of L-ascorbic acid with citric acid in comparison to fruits
only with an L-ascorbic acid addition. This is caused by a shift in the
reaction equilibrium between the AC and citric acid toward the AC,
which is a more durable substance.
As a potent antioxidant, AC has the capacity to eliminate several
different reactive oxygen species, keep the membrane-bound
antioxidant a-tocopherol in the reduced state, act as a cofactor
maintaining the activity of a number of enzymes (by keeping metal
ions in the reduced state); it also appears to be the substrate for
oxalate and tartrate biosynthesis and has a role in stress resistance
(Klein & Kurilich, 2000). Existing data pertain mainly to investigations
into the changes of L-ascorbic acid during convective
drying of fruits. The retention of L-ascorbic acid during fruit drying
is a function of process conditions. AC is seriously affected by a high
drying temperature (Ramallo and Mascheroni, 2012). Furthermore,
we showed that the pulping of cranberries before drying leads to a
lower degradation of AC during freezeedrying.