The determination of the total antioxidant activity of beetroot
juice mixed with fruit based acidity regulators to obtain final pH of
about 3.5 was carried out by spectrophotometric batch test
employing ABTSþ radical. Reference samples were also prepared
by mixing beetroot juice withwater or water with the fruit juices in
corresponding proportions (Table 1). These solutions served as
controls of the input of individual diluted components into antioxidant
potential of the respective mixtures. This allowed to
recognize whether the tested fruit based regulators contained antioxidants
that act synergistically with beetroot components e
increasing, or antagonistically - lowering the antioxidant activity of
the mixture, compared to the additive effect. The latter occurs
when antioxidant activity is equal to the sum of determined activities
for the individual components.
The total antioxidant activities of the “pH 3.5 MIX-es” are shown
in Table 3. The most commonly used acidity regulator, i.e. citric acid,
did not display a positive influence on antioxidative potential of the
respective “pH 3.5 MIX”. Only after two weeks' storage, it seemed to decrease the degradation of beetroot antioxidants; TE value was
69% higher than in pure beetroot juice. Among the samples studied,
the highest values of TE parameter were measured for beetroot
juice mixed with blue-berried honeysuckle juice, next in order was
the “pH 3.5 MIX” of beetroot juice with sea buckthorn juice.
In the case of all fruit based acidity regulators, a similar pattern
of changes in antioxidant activity of tested “pH 3.5 MIX-es” after
different storage periods was observed. After one week at 4 C, the
antioxidant potential of all samples decreased, which may indicate
degradation of some reducing components. After subsequent week
of storage, for samples containing juices of mirabelle plum, sea
buckthorn and blue-berried honeysuckle, the antioxidant activity
increased by 15e55 % in comparison to the previous storage period.
This may result from the fact that betalains in acidic environment
degrade and after some storage period they are being resynthesized.
In the controls containing citric acid or lemon juice, the
decrease of antioxidant activity continued also after the second
storage period. However, no clear synergistic/antagonistic effects
between fruit and beetroot juices was seen. Most of the mixtures
showed lower antioxidant potential than the sum of their individual
components (Table 3), though the exceptionswere observed,
especially in the case of “pH 3.5 MIX-es” containing lemon (TE value
23% above the additive effect) or mirabelle plum (TE value 6% above
the additive effect) juices.