3.5.4. Oxidative stability index (OSI)
The results showing the effect of Senjed peel aqueous extract compared
to positive control (TBHQ) and negative control (T0) samples on the
oxidative stability of cold-pressed sesame oil are presented in Fig. 4.
There was statistically significant differences between different
treatments (p<0.05 ). As expected, samples without the
addition of any antioxidants (T0) were oxidized easily, and indicated
the lowest OSI values (9.05 h). In contrast, samples containing
synthetic antioxidants (TTBHQ) and the highest concentration of extract
(T750) showed the highest index of oxidative stability index (both 15.39
h). As can be seen, with increasing the concentration of the extract,
the oxidative stability of the oil samples increases and at a
concentration of 750 ppm, it is equivalent to a sample containing
synthetic antioxidant TBHQ. Except T100 treatment, the OSI values of
oils with added Senjed peel aqueous extract or synthetic antioxidants
were found to be significantly larger (p< 0.05 ) than
that of the negative control oils (T0). Incorporation of soybean,
cottonseed and rice bran oils with rosemary extract resulted
significantly (p< 0.05 ) higher OSI values than that of
oil with added synthetic antioxidant (BHA + BHT) (Yang et al., 2016).