Page 34 - Natural Antioxidants, Applications in Foods of Animal Origin

Mechanism of Oxidation in Foods of Animal Origin 13
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Like most chemical reactions, lipid oxidation rates increase with increasing
temperature and time (Hultin, 1992). Saeed and Howell (2002) reported
that the rate of lipid oxidation in frozen Atlantic mackerel increased with
increasing storage time and storage temperature. Furthermore, freezing can
facilitate lipid oxidation, partly because of concentration effects (Foegeding
et al., 1996). The influence of long-term frozen storage, temperature (−25 and
−45 °C) and type of packaging materials (low and medium oxygen barriers)
on the lipid oxidation of frozen Atlantic herring fillets (Clupea harengus)
was studied by Tolstorebrov et al. (2014). The lowest lipid oxidation in term
of PV and thiobarbituric acid reactive substances (TBARS) was detected in
frozen Atlantic herring fillets kept at −45 °C and the packaging material with
a medium oxygen barrier. From the result, the oxygen concentration in the
package was considered to be the dominating factor for the herring’s oxida-
tion during frozen storing.
Cooked meats held in a refrigerator develop rancid odors and flavors
which usually become apparent within 48 h at 4 °C. These flavors are
particularly noticeable after reheating the meat and are referred to as WOF
(Tims & Watts, 1958). The rapid development of oxidized flavor in refrig-
erated cooked meats is in marked contrast to the slow onset of rancidity
commonly encountered in raw meats, fatty tissues, rendered fat, or lard,
which is normally not apparent until they have been stored for weeks or
months (Pearson et al., 1977).
Heating results in the release of heme-bound iron and in forming other
polymers with proteins; those polymers enhance the catalytic effect of iron.
This is also true with respect to the thermal inactivation of enzymes that
contain metals acting as prosthetic groups (e.g., LOX and peroxidases).
These enzymes, even after denaturation, are capable of catalyzing oxida-
tion. On the other hand, heating does not release iron from ferritin, but does
enhance its reduction (Kanner, 1992). The rate of oxidation in the presence
of metals is higher at lower pH than at neutral pH for Fe and Fe (Richards
3+
2+
& Hultin, 2000).
The extent of lipid oxidation in cooked meat appears to be related to the
intensity of heat treatment. Pearson et al. (1977) reported that meat heated
at 70 °C for 1 h developed rancidity rapidly. However, thiobarbituric acid
(TBA) values decreased when the cooking temperature was raised above
80 °C. According to Huang and Greene (1978), meat subjected to high
temperatures and/or long periods of heating developed lower TBA values,
than did samples subjected to lower temperature for a shorter period of time.