ABSTRACT
BACKGROUND:
Due to the recent emerging information on the
antioxidant properties of soy products, substitution of
soy milk for
milk in the
diet has been proposed by some
nutritionists. We aimed to compare four distinct
antioxidant measuring
methods in the evaluation of
antioxidant properties of industrial ultra-high
temperature (UHT)
milk, UHT
soy milk, and their fermented products by
Lactobacillus plantarum A7. MATERIALS AND
METHODS:
Ascorbate auto-
oxidation inhibition assay, 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH)
free radical scavenging
method,
hydrogen peroxide neutralization assay and reducing activity test were compared for the homogeneity and accuracy of the results.
RESULTS:
The results obtained by the four tested
methods did not completely match with each other. The results of the DPPH assay and the reducing activity were more coordinated than the other
methods. By the use of these
methods, the
antioxidant capability of UHT
soy milk was measured more than UHT
milk (33.51 ± 6.00% and 945 ± 56 µM
cysteine compared to 8.70 ± 3.20% and 795 ± 82 µM
cysteine). The negative effect of
fermentation on the
antioxidant potential of UHT
soy milk was revealed as ascorbate auto-
oxidation inhibition assay, DPPH
method and reducing activity tests ended to approximately 52%, 58%, and 80% reduction in
antioxidant potential of UHT
soy milk, respectively.
CONCLUSIONS:
The antioxidative properties of UHT
soy milk could not be solely due to its phenolic components.
Peptides and
amino acids derived from thermal processing in
soy milk probably have a main
role in its
antioxidant activity, which should be studied in the
future.