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R
HO
1
: COOH
6
:
H
COOH
HO
2
COOH
HO
3
COOH
HO
4
COOH
HO
5
Fig. 9.1.
Chemical structures of anacardic acids and related compounds. See text for names.
a model, because this particular anacardic
acid was available from our previous study
(Kubo
et al.
, 1986).
vitamin E, inhibited linoleic acid peroxidation
by almost 50% at a concentration of 30 mg/ml.
However, neither anacardic acid (C
15:3
) nor
salicylic acid inhibited this oxidation at the
same concentration. The negative result of
anacardic acid (C
15:3
) can be explained by
their structural feature in which the electron-
donating alkenyl group is located at the
meta
-position to the hydroxyl group so that
it does not stabilize the phenoxy radicals
(Cuvelier
et al.
, 1992). Salicylic acid does
not possess any alkyl group, however.
Cardanol (C
15:3
) inhibited linoleic acid per-
oxidation by about 30% at a concentration
of 30 mg/ml, but this inhibitory activity is
still less than that of a-tocopherol. The
results observed indicate that anacardic
acids are unlikely to act as radical scaven-
gers because they do not have the ability to
donate a hydrogen atom to the peroxy radi-
cal derived from the auto-oxidizing fatty
acids. Further evidence for this conclusion
9.4
Lipid Peroxidation
Lipid peroxidation is known to be one of
the reactions set into motion as a conse-
quence of the formation of free radicals in
cells and tissues. Membrane lipids are abun-
dant in unsaturated fatty acids. Linoleic
acid is particularly a target of lipid peroxi-
dation. The effect of anacardic acid (C
15:3
)
and salicylic acid on the autoxidation of
linoleic acid was first tested by the ferric
thiocyanate method as previously described
(Osawa and Namiki, 1981). In a control
reaction, the production of lipid peroxide
increased almost linearly during 8 days of
incubation. a-Tocopherol, also known as
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