Page 32 - Natural Antioxidants, Applications in Foods of Animal Origin

Mechanism of Oxidation in Foods of Animal Origin 11
VetBooks.ir unsaturated fatty acids primarily reacting with molecular oxygen via a

free radical chain mechanism (Gray, 1978). The primary autooxidation is
followed by a series of secondary reactions which lead to the degradation of
the lipid and the development of oxidative rancidity. The main unsaturated
fatty acids comprising the lipids of animal tissues are oleic, linoleic, linolenic,
and arachidonic acids. Their autoxidation gives rise to a number of different
hydroperoxides which, in conjunction with the many different decompo-
sition pathways involved, lead to a large number of volatile compounds
(Mottram, 1987). Oxidation of lipids also occurs during postmortem storage
of muscle tissue. Meats such as fish and poultry contain a high concentration
of PUFA and are therefore more susceptible to oxidation (Pacheco-Aguilar
et al., 2000; Apgar & Hultin, 1982). Thus, fish lipids undergo more rapid
oxidation after capture, even at low temperature storage (Foegeding et al.,
1996; Pacheco-Aguilar et al., 2000). Pacheco-Aguilar et al. (2000) reported
that the shelf life of oily Monterey sardine was limited by lipid oxidation, as
shown by the increase of peroxide value (PV) during storage at 0 °C up to 15
days. Sohn et al. (2005) reported that the total lipid hydroperoxide content of
Pacific saury (Cololabis saira), Japanese Spanish mackerel (Scomberomorus
niphonius), and chub mackerel (Scomber japonicus) tended to increase in
both dark and ordinary muscle throughout four days of iced storage. Fatty
fish such as sardine and mackerel underwent rapid lipid oxidation during
iced storage due to the high content of PUFA (Chaijan et al., 2006; Chaijan
et al., 2013; Pacheco-Aguilar et al., 2000). Lipid oxidation seems to be a
distinct problem in surimi made from some dark-fleshed fish and particu-
larly surimi from mammalian and avian muscle (Lanier, 2000). Lynch et al.
(2001) demonstrated that lipid oxidation occurred progressively in stored
ground beef at 4 °C and produced a variety of aldehydes.

1.4.2 ENDOGENOUS ANTIOXIDANTS

The normal resistance of meat to the development of rancidity depends on
the balance between the presence of AH in the animal tissues and the level of
unsaturation and the concentration of the fatty acids present (Enser, 1987).
The living cells possess several protection mechanisms directed against
lipid oxidation products (Sies, 1997). Glutathione peroxidase reduces
hydroperoxides in the cellular membranes to the corresponding hydroxy-
compounds. This reaction demands supply of reduced glutathione and will
therefore cease post mortem when the cell is depleted of that substance.
The membranes also contain the phenolic compound α-tocopherol (Vitamin