Antioxidant activity of OOE in stripped FO during storage
Antioxidant activity often depends on the type of oil used. For example,
while 0.2% grapefruit seed extract had similar antioxidant activity to
0.01% TBHQ in palm oil, the extract had significantly lower activity
than 0.01% TBHQ in FO (Safakar et al., 2016).
As another example, 0.25% extract
of spent coffee ground had stronger antioxidant activity than 0.02% BHT
in stripped SBO, but it showed much weaker activity than 0.02% BHT in
stripped FO (Hwang et al., 2019). The different activity of an
antioxidant in different oils is attributed to different fatty acids
composition and inherent antioxidants in oil (Safakar et al., 2016).
Since differences in antioxidant activity were also observed between
stripped SBO and stripped FO where inherent antioxidants were completely
removed (Hwang et al., 2019), the fatty acid composition alone can
affect the activity of an antioxidant.
To understand the antioxidant activity of OOE in different oils, the
storage study was also conducted in stripped FO. As shown in Figure 3a,
PV of the control FO and those of FO containing 0.1% Toco and 0.1% RE
quickly increased and reached a peak value in 2 days at 25 ℃. In
contrast, PV of FO samples containing
0.1% OOE and 0.02% BHT increased
more slowly. On day 2, while FO samples with 0.1% OOE and 0.02% BHT
had PV of 4.90 ± 0.17 and 5.43 ± 0.12 meq/Kg, respectively, those with
0.1% Toco and 0.1% RE had significantly higher PV (12.33 ± 0.45 and
10.88 ± 0.0.35 meq/Kg, respectively). On day 5, while PV of FO with
0.02% BHT increased to 11.80 ± 0.78 meq/Kg, that with 0.1% OOE was
significantly lower (8.89 ± 0.24 meq/Kg) indicating stronger antioxidant
activity of 0.1% OOE than 0.02% BHT in FO. As shown in Figure 3b, CDV
of FO with 0.1% OOE and 0.02% BHT were the lowest throughout the
course of storage at 25 ℃. FO with OOE had slightly, but not
significantly, lower CDV (11.33 ± 0.24 mmol/L) than that with BHT (13.80
± 0.07 mmol/L) at day 28. CDV at day 10 indicated that Toco had stronger
antioxidant activity (12.87 ± 0.29
mmol/L) than RE (21.66 ± 1.31
mmol/L), which was opposite to the trend shown in SBO. CDV at day 28
also showed that Toco had stronger antioxidant activity (22.56 ± 0.42
mmol/L) than RE (45.68 ± 13.16 mmol/L) in FO at 25 ℃. p -AV of FO
with 0.1% RE also increased faster than that with 0.1% Toco confirming
the stronger antioxidant activity of Toco than RE in FO (Fig. 3c). On
day 28, FO with 0.1% OOE had significantly lower p -AV (32.49 ±
0.39) than that with 0.02% BHT (53.43 ± 0.61) indicating the stronger
antioxidant activity of 0.1% OOE than 0.02% BHT. FO with RE had lowerp -AV (100.68 ± 10.88) than the control (218.45 ± 5.29) on day 10,
but had even higher p -AV (564.02 ± 5.76) than the control (210.92
± 0.65) on day 28. p -AV can reach a peak value and then decrease
(Adjonu et al., 2019), and it is possible that the p -AV of the
control might have reached its peak value and then decreased between
days 10 and 28.
Figure 4a shows PV of FO samples at 40 ℃. The PV of the control and FO
samples with 0.1% Toco and 0.1% RE reached peak values in 1 day (11.26
± 1.03, 10.91 ± 0.82 and 11.31 ±
0.40 meq/Kg, respectively). FO with 0.1% OOE had the lowest PV on day 1
(7.18 ± 0.21 meq/Kg) followed by 0.02% BHT (9.58 ± 0.05 meq/Kg)
indicating stronger antioxidant activity of 0.1% OOE compared to 0.02%
BHT in FO at 40 ℃. FO with 0.1% RE had a higher CDV (24.23 ± 1.06
mmol/L) than FO with 0.1% Toco (12.45 ± 0.45 mmol/L) on day 5 as well
as day 10 (28.84 ± 3.13 and 18.03 ± 0.21 mmol/L, respectively) (Fig. 4b)
indicating stronger antioxidant activity of Toco than RE in FO. FO
samples with 0.1% OOE and 0.02% BHT had the lowest CDV throughout the
course of storage at 40 ℃. 0.1% RE did not show very strong activity in
preventing p -AV of FO at 40 ℃ while all other treatments had
significantly lower p -AV compared to the control FO (Fig. 4c). FO
with 0.1% OOE had slightly, but not significantly, lower p -AV
(23.15 ± 0.77) than those with 0.02% BHT and 0.1% Toco (33.76 ± 0.38
and 33.83 ± 0.97, respectively) on day 28. In general, the order of
antioxidant activity in FO was OOE ≥ BHT > Toco
> RE, which was somewhat different from the trend with SBO.
Since stripped oils were used in this study, the different activity
trends in the two different oils is attributed to their fatty acid
compositions.