Food Biochemistry and Food Processing

298 Part III: Muscle Foods

marine mammalians such as dolphins and whales
(Aristoy et al. 2003).

Free Amino Acids

The action of muscle aminopeptidases contributes to
the generation of free amino acids in living muscle.
An example of the typical content of free amino
acids, at less than 45 minutes postmortem, in gly-
colytic and oxidative porcine muscles is shown in
Table 13.4. It can be observed that most of the amino
acids are present in significantly higher amounts in
the oxidative muscle (Aristoy and Toldrá 1998). The
free amino acid content is relatively low just post-
mortem, but it is substantially increased during post-
mortem storage due to the action of the proteolytic
chain, which is very active and stable during meat
aging.

MUSCLE ANDADIPOSETISSUELIPIDS

Skeletal muscle contains a variable amount of lipids,
between 1 and 13%. Lipid content mainly depends

on the degree of fattening and the amount of adipose

tissue. Lipids can be found within the muscle (intra-

muscular), between muscles (intermuscular), and in

adipose tissue. Intramuscular lipids are mainly com-

posed of triacylglycerols, which are stored in fat

cells, and phospholipids, which are located in cell

membranes. The amount of cholesterol in lean meat

is around 50–70 mg/100 g. Intermuscular and adi-

pose tissue lipids are mainly composed of triacyl-

glycerols and small amounts of cholesterol, around

40–60 mg/100g (Toldrá 2004).

Triacylglycerols

Tri-acylglycerols are the major constituents of fat, as

shown in Table 13.1. The fatty acid content mainly

depends on age, production system, type of feed,

and environment (Toldrá et al. 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 nutrient and fatty acid compo-

sition are somehow standardized due to biohydro-

Table 13.4.Example of the Composition in Free Amino Acids of the Glycolytic Muscle

Longissimus dorsiand Oxidative Muscle Trapezius

M. Longissimus dorsi M. Trapezius

Amino acids (mg/100 g muscle) (mg/100 g muscle)

Essential
Histidine 2.90 4.12
Threonine 2.86 4.30
Valine 2.78 2.09
Methionine 0.90 1.01
Isoleucine 1.52 1.11
Leucine 2.43 1.82
Phenylalanine 1.51 1.25
Lysine 2.57 0.22

Non-essential
Aspartic acid 0.39 0.74
Glutamic acid 2.03 5.97
Serine 2.02 4.43
Asparragine 0.91 1.63
Glycine 6.01 12.48
Glutamine 38.88 161.81
Alanine 11.29 26.17
Arginine 5.19 5.51
Proline 2.83 4.45
Tyrosine 2.11 1.63
Ornithine 0.83 0.83
Source:From Aristoy and Toldrá 1998.