BLBS102-c15 BLBS102-Simpson March 21, 2012 13:21 Trim: 276mm X 219mm Printer Name: Yet to Come
15 Biochemistry of Raw Meat and Poultry 291Table 15.4.Example of the Composition in Dipeptides
(Expressed as mg/100g of Muscle) of the Porcine
Glycolytic MuscleLongissimus Dorsi and Oxidative
MuscleTrapezius.Carnosine AnserineEffect of muscle metabolism
Glycolytic(muscleLongissimus dorsi) 313 14.6
Oxidative(muscle. Trapezius) 181.0 10.7
Animal species
Pork (loin) 313.0 14.5
Beef (top loin) 372.5 59.7
Lamb (neck) 94.2 119.5
Chicken (pectoral) 180.0 772.2Source: Aristoy and Toldr ́a 1998, Aristoy and Toldr ́a 2004.TriacylglycerolsTriacylglycerols are the major constituents of fat, as shown in
Table 15.1. The fatty acid content mainly depends on age, pro-
duction system, type of feed, and environment (Toldraetal. ́
1996b). Monogastric animals such as swine and poultry tend to
reflect the fatty acid composition of the feed in their fat. In the
case of ruminants, the nutrients and fatty acid composition are
somehow standardized due to biohydrogenation by the microbial
population of the rumen (Jakobsen 1999). The properties of the
fat will depend on its fatty acid composition. A great percentage
of the triacylglycerols are esterified to saturated and monounsat-
urated fatty acids (see neutral muscle fraction and adipose tissuedata in Table 15.5). When triacylglycerols are rich in polyunsat-
urated fatty acids (PUFA) 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 temperature.PhospholipidsThese compounds are present in cell membranes, and although
present in minor amounts (see Table 15.1), they have a strong
relevance to flavor development due to their relatively high
proportion of PUFA (see polar fraction in Table 15.5). Ma-
jor constituents are phosphatidylcholine (lecithin) and phos-
phatidylethanolamine. The phospholipid content may vary de-
pending on the genetic type of the animal and the anatomical
location of the muscle (Hern ́andez et al. 1998, Armero et al.
2002). For instance, red oxidative muscles have a higher amount
of phospholipids than white glycolytic muscles.CONVERSION OF MUSCLE TO MEAT
A great number of chemical and biochemical reactions 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 conversion of muscle to meat; this process is
basically schematized in Figure 15.2 and consists of the follow-
ing steps: Once the animal is slaughtered, the blood circulation
is stopped, and the importation of nutrients and the removal of
metabolites to the muscle cease. This fact has very importantTable 15.5.Example of Fatty Acid Composition (Expressed as Percentage of Total Fatty Acids) of Muscle
Longissimus Dorsi and Adipose Tissue in Pigs Feeded with a Highly Unsaturated Feed. Neutral and Polar Fractions
of Muscle Lipids are also IncludedFatty Acid TotalMuscle
Neutral PolarAdipose
TissueMyristic 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
Stearic 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 MUFA/SFA 1.01 1.15 0.33 0.91
Ratio PUFA/SFA 0.53 0.33 1.37 0.79SFA, saturated fatty acids; MUFA, monosaturated fatty acids; PUFA, polysaturated fatty acid.