13 Biochemistry of Raw Meat and Poultry 299
genation by the microbial population of the rumen
(Jakobsen 1999). The properties of the fat will de-
pend on its fatty acid composition. A great percent-
age of the triacylglycerols are esterified to saturated
and monounsaturated fatty acids (see neutral muscle
fraction and adipose tissue data in Table 13.5). When
triacylglycerols are rich in polyunsaturated fatty
acids such as linoleic and linolenic acids, fats tend to
be softer and prone to oxidation. These fats may even
have an oily appearance when kept at room temper-
ature.
Phospholipids
These compounds are present in cell membranes,
and although present in minor amounts (see Table
13.1), they have a strong relevance to flavor devel-
opment due to their relatively high proportion of
polyunsaturated fatty acids (see polar fraction in
Table 13.5). Major constituents are phosphatidyl-
choline (lecithin) and phosphatidylethanolamine.
The phospholipid content may vary depending on
the genetic type of the animal and the anatomical
location of the muscle (Armero et al 2002, Her-
nández et al. 1998). For instance, red oxidative mus-
cles have a higher amount of phospholipids than
white glycolytic muscles.
CONVERSION OF MUSCLE TO
MEAT
A great number of chemical and biochemical reac-
tions take place in living muscle. Some of these
reactions continue, while others are altered due to
changes in pH, the presence of inhibitory com-
pounds, the release of ions into the sarcoplasm, and
so on during the early postmortem time. In a few
hours, these reactions are responsible for the conver-
sion of muscle to meat; this process is basically
schematized in Figure 13.2 and consists of the fol-
lowing steps: Once the animal is slaughtered, the
blood circulation is stopped, and the importation of
nutrients and the removal of metabolites to the mus-
cle cease. This fact has very important and drastic
consequences. The first consequence is the reduc-
tion of the oxygen concentration within the muscle
cell because the oxygen supply has stopped. An im-
mediate consequence is a reduction in mitochondrial
Table 13.5.Example of Fatty Acid Composition (Expressed as Percent of Total Fatty Acids) of
Muscle Longissimus dorsiand Adipose Tissue in Pigs Fed with a Highly Unsaturated Feed
(Neutral and Polar Fractions of Muscle Lipids Also Included)
Muscle
Fatty Acid Total Neutral Polar Adipose Tissue
Myristic acid (C 14:0) 1.55 1.97 0.32 1.40
Palmitic acid (C 16:0) 25.10 26.19 22.10 23.78
Estearic acid (C 18:0) 12.62 11.91 14.49 11.67
Palmitoleic acid (C 16:1) 2.79 3.49 0.69 1.71
Oleic acid (C 18:1) 36.47 42.35 11.45 31.64
C 20:1 0.47 0.52 0.15 0.45
Linoleic acid (C 18:2) 16.49 11.38 37.37 25.39
C 20:2 0.49 0.43 0.66 0.78
Linolenic acid (C 18:3) 1.14 1.17 0.97 2.64
C 20:3 0.30 0.10 1.04 0.10
Arachidonic acid (C 20:4) 2.18 0.25 9.83 0.19
C 22:4 0.25 0.08 0.84 0.07
Total SFA 39.42 40.23 37.03 37.02
Total MUFA 39.74 46.36 12.26 33.81
Total PUFA 20.84 13.41 50.70 29.17
Ratio M/S 1.01 1.15 0.33 0.91
Ratio P/S 0.53 0.33 1.37 0.79