Chemistry Reference
In-Depth Information
Fig. 12.23 Reaction of nitroxyl radicals with carbon- or oxygen-centered radicals.
HALS. While it is only `half' hindered, it is a very effective antioxidant. See
Section 12.4.6, above. Its use in foods, however, is very highly restricted. In the
United States, ethoxyquin can be used to stabilize fish meal and to stabilize the
color of ground paprika. In the absence of ethoxyquin, highly unstable fish meal
is known to spontaneously combust and the incorporation of this antioxidant is
necessary for its safe transport and storage (de Koning, 2002). Ethoxyquin is an
extraordinarily effective antioxidant for polyunsaturated fats. The mechanism of
action of ethoxyquin has been the subject of much research and debate. In
mechanistic thinking analogous to that involving HALS, Lin and Olcott (1975)
described the formation of the nitroxyl radical of ethoxyquin, and suggested it
was responsible for ethoxyquin's antioxidative effect. That work was supported
by Gunstone et al. (1991) who showed that the nitroxyl was formed upon
oxidation of an initially formed aminyl radical. KÏÂÏ and Taimr (1993) however
suggested that the antioxidative effect of ethoxyquin was due in some measure
to hydrogen donation from the 4-methyl group, and isolated a dimeric product
that retained some antioxidative activity. Taimr (1994) further stated that the
nitrosyl radical of ethoxyquin `acts as an efficient antioxidant which, however,
does not participate in the cyclic mechanism that is employed to explain the
action of antioxidants of the HALS type.' de Koning (2002) returned to the idea
that ethoxyquin is an effective antioxidant because two oxidation products, 1,8
0
-
di-(1,2-dihydro-6-ethoxy-2,2,4-trimethylquinoline and 2,6-dihydro-2,2,4-
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