Page 30 - Natural Antioxidants, Applications in Foods of Animal Origin

Mechanism of Oxidation in Foods of Animal Origin 9
VetBooks.ir acid. LOX use molecular oxygen to catalyze the stereo and regiospecific

oxygenation of PUFA with 1-cis, 4-cis-pentadiene moieties (Kolakowska,
2002). LOX react enzymatically with more than one methylene carbon on
the substrate molecule to yield double oxygenation sites (German et al.,
1992). The newly formed fatty acid peroxy free radical removes hydrogen
from another unsaturated fatty acid molecule to form a conjugated hydro-
peroxy diene. LOX forms a high-energy (radical) intermediate complex with
the substrate; this complex is capable of initiating the oxidation of lipids
and other compounds (e.g., carotenoids, chlorophyll, tocopherols, thiol
compounds, and protein), which can themselves interact with the enzyme
substrate complex as well (Hammer, 1993; Hultin, 1994).
Kolakowska (2002) reported that mammalian LOX are categorized
according to the positional specificity of oxygen insertion into arachi-
donic acid. Four isoform positions of arachidonate LOX have been identi-
fied: 5-LOX (E.C. 1.13.11.34), 8-LOX, 12-LOX (E.C. 1.13.11.31), and
15-LOX (E.C. 1.13.11.33). The LOX that catalyzes oxidation of linoleate
(E.C.1.13.11.12) attacks linoleic acid, both at position 9 and position 13.
In chicken meat arachidonate, 15-LOX was found to be active during
12-month storage at −20 °C (Grossman et al., 1988). In frozen-stored
fish, LOX contributes to oxidative lipid deterioration. However, LOX in
fish is also responsible for the formation of desirable fresh fish flavor, the
seaweed flavor (Lindsay, 1994). Some species show a higher activity of
12-LOX, while 15-LOX is more active in others; for this reason, the fresh
fish flavor spectrum is species dependent. The half-lives of 12- and 15-
LOX at 0 °C were less than 3 h and more than 10 h, respectively (German
et al., 1992). LOX was observed to be active in cold-stored fish after 48 h
of storage (Medina et al., 1999). The storage of herring, three weeks at
−20 °C, resulted in an increase in LOX activity. During prolonged frozen
storage of herring, a decrease in LOX activity was observed (Samson &
Stodolnik, 2001). Sae-leaw et al. (2013) reported that the development of
fishy odor in Nile tilapia skin during iced storage was mostly governed by
lipid oxidation via autoxidation or induced by LOX. Although the partici-
pation of LOX in the post mortem animal lipid oxidation is acknowledged,
the role of LOX in lipid oxidation is much more important in plant than
in animal food products. LOXs are responsible for the off flavor in frozen
vegetables (Ganthavorn et al., 1991), lipid oxidation in cereal products,
rapeseed, pea, avocado, and muscle foods, and for the beany and bitter
flavor (Frankel, 1998).