180 Chapter 8
2004 ). Increased levels of oil or oilseed seeds
in the diet can also increase the levels of α -
tocopherol found in the meat (Leskanich et
al. 1997 ). Increased levels of α - tocopherol or
Vitamin E fed to pigs can result in lower
TBARS (Corino et al. 1999 ; Hasty et al.,
2002 )) and thus less oxidation of the lipids
(Corino et al. 1999 ).
Warmed - over fl avor (WOF) occurs in
uncured products after they are cooked.
Nitrites in cured products function as a potent
inhibitor of WOF development. As little as
50 ppm of nitrites effectively prevents lipid
oxidation (Sato and Hegarty 1971 ). However,
one of the most noticeable reactions in meat
when nitrites are fi rst added is the oxidation
of the heme pigments to the ferric form (Fox
and Benedict 1987 ). Nitrite is readily reduced
by endogenous reductants in the meat to form
nitric oxide, which combines with myoglobin
to form the cured - meat pigment (Fox and
Benedict 1987 ). The nitric oxide is an effi -
cient radical chain terminator that slows the
propagation of lipid oxidation (Fox and
Benedict 1987 ). Other antioxidant properties
have been suggested for nitrite.Vitamins
Most of the effects cooking has on meat are
positive: improved palatability, reduction of
bacteria, and fl avor development. However,
cooking does have a negative impact on the
vitamin content of meat, especially water -
soluble vitamins such as thiamine, ribofl avin,
and niacin (Al - Khalifa et al. 1993 ; Lombardi -
Boccia et al. 2005 ; Riccio et al. 2006 ).
Reported retention of vitamins, however, is
much more variable, with retention of thiamin
being reported as low as 39% (Al - Khalifa
et al. 1993 ) and as high as 66% (Rhee et al.
1993 ).
Severity of heating has a major impact on
the retention of water - soluble vitamins
(Riccio et al. 2006 ). Kumar and Aalbersberg
(2006) reported that microwave oven cooking
tended to retain higher amounts of vitamins.products. Although the ingredients have
some infl uence on peelability, proper cooking
without excess weight loss and wrinkling are
important in imparting good peelability. The
cooking process must be carefully controlled
to make the product readily peelable and of
good appearance.
Lipids
The changes that occur during cooking also
affect lipids. Oxidation of lipids occurs
when oxygen is present and will occur at
a faster rate as the temperature increases.
These changes in lipids help to give the char-
acteristic odor and fl avor of cooked meat.
Cooked meat exposed to oxygen results in
further lipid oxidation, which can cause off -
fl avors and odors to appear in just a few
hours. This off - fl avor development has been
traditionally referred to as “ warmed - over ”
fl avor. More recently, some researchers have
referred to the process as cooked - meat fl avor
deterioration.
Oxidation of lipids in whole - muscle prod-
ucts occurs relatively slowly unless a catalyst
is present. In processed products, salt acts
as a catalyst and can result in rapid lipid
oxidation. For many years, researchers have
investigated what catalyzes the oxidation of
lipids in fresh cooked meats. During cooking,
the muscle cells are broken, allowing high
molecular weight iron sources to be released
(Morrissey et al. 1998 ). Denatured heme iron
from myoglobin is one possible candidate for
catalysis, along with free iron (Fox and
Benedict 1987 ).
The stability of the lipids during cooking
is affected by the fatty acid makeup of the
lipids and dietary compounds that can func-
tion to reduce oxidation. Increasing the
degree of unsaturated fatty acids will reduce
lipid stability. Also, altering diet to include
rapeseed oil, corn oil, or oil seed meals will
increase the unsaturated fats in the meat. This
is especially true in pork and poultry (Romans
et al. 1995 ; Corino et al. 2002 ; Rey et al.