oxidized tocopherols produced in th

oxidized tocopherols produced in this system which compensated the
protective effect of the remaining tocopherols.
3.2. Effect of metal chelator on the oxidative stability of base algae oil
During lipid oxidation procedure, transition metals are critical to a
chain reaction process because of their participation in lipid hydroperoxides decomposition which yield reactive free radicals, such as lipid
peroxyl and alkoxyl radicals that initiate free radical chain oxidation
(Goddard, McClements, & Decker, 2012). In the strategies of preventing
lipid oxidation, incorporating metal chelators is usually an efficient way
to delay the oxidation. Some study found polyphenols can act as a metal
chelator in oil so that they could delay the consumption of other antioxidants (Leopoldini, Russo, & Toscano, 2011). In order to understand if
the protective role of hydrophilic antioxidants, e.g., AA and GTE on α-
tocopherol degradation was due to the metal chelating properties, the
role of a commercial metal chelator, desferoxiamine (DFO) and EDTA
on the oxidative stability of base algae oil in the presence of hydrophilic
antioxidants were examined as shown in the formation of propanal in
Fig. 4.
We investigated the role of 50 μM DFO or EDTA on the antioxidative
effect of AA under different concentrations (50, 150, 250 μM) against
base algae oil oxidation (Fig. 4A and B). DFO is a chelator solo for ferric
ion and EDTA mainly binds with ferrous. The addition of DFO and EDTA
showed no antioxidative effect on base algae oil oxidation and the
formation of propanal was close to the blank at the same storage time.
This could happen if there is no transition metal associated with algae
oil oxidation. When combining the metal chelator with AA, no synergistic effect was observed at all the concentrations studied and the lag
phase was attributed to the existence of AA. The same experiments
were carried out by replacing AA with 300 μM GSE, GSE-p, GTE and
RA (Fig. 4C). The result was consistent with the system in the absence
of metal chelator which again suggested that metal chelator did not feature any antioxidative effect on base algae oil oxidation, nor enhance the
efficacy of hydrophilic antioxidants including phenolic antioxidants.
Some studies on the oxidative stability of extra virgin olive oil in the
presence of copper ion found that the tocopherols was quickly consumed in the absence of polyphenols but it was largely saved in the
presence of polyphenols (Keceli & Gordon, 2006; Paiva-Martins & Gordon, 2005). The author suggested that polyphonic compounds acted
as a metal chelator which precluded the degradation of tocopherols
(Bendini, Cerretani, Vecchi, Carrasco-Pancorbo, & Lercker, 2006). Our
previous investigation found that only ferric ion could promote the depletion of α-tocopherol in MCT oil and some types of phospholipids
could decelerate the loss of α-tocopherol by binding with metal ions
(Chen, Panya, McClements, & Decker, 2012). If the mechanism of hydrophilic antioxidants to retard base algae oil oxidation by sparing tocopherols was to sacrifice themselves reacting with transition metals, DFO
and EDTA which owning strongest affinity to either high-valence or
low-valence transition metals were expected to restrain the loss of