The TBA test determines the amount of malondialdehyde
(MDA), a major secondary by-product of lipid oxidation in food
samples. Based on our results revealed in Fig. 4, TBA values of different
samples, as influenced by storage time were minimum and
had less differences at the start of the study. However, these value
increased significantly (P < 0.05) as the time of storage. TBA value
showed an increasing trend until day 12 in all samples except
OLENW and OLENWP. The samples containing encapsulated olive
leaf extract by WPC and pectin (OLENW and OLENWP) showed a
peak in day 8, and then TBA values decreased. When measuring
TBA value, malondialdehyde reacts with thiobarbituric acid. Thus,
the rate of thiobarbituric acid increases during oil oxidation. In this
process, aldehydes may be oxidized to carboxylic acids, so the
amount of thiobarbituric acid will decrease. According to
Taghvaei et al. (2014), this could be related to the oxidation of secondary
autoxidation products and formation of carboxylic acids.
Our result indicated that the highest and lowest TBA value was
related to blank and TBHQ containing samples, respectively. In
general, TBA value for oil samples containing encapsulated olive
leaf extract with pectin–WPC had a similar behavior with TBHQ
samples. This could indicate the high capability of this form of
nano-encapsulation for natural olive leaf phenolic compounds
which can compete with a synthetic antioxidant due to better
controlled release, and a supplementary antioxidant activity of
WPC and pectin.