2009_Book_FoodChemistry

566 12 Meat
Fig. 12.1. The structural element of skeletal muscle (according to Gault, 1992). 1 epimysium, 2 perimysium,
3 endomysium, 4 muscle fiber
Fig. 12.2. A cross-section of
M. psoas rabbit muscle. (From
Schultz, Anglemier, 1964)
somes). Under aerobic conditions, the bulk of the
cellular energy is produced in the form of ATP in
the mitochondria. The lysosomes are the source
of the endopeptidases which participate in the
aging of meat (cf. 12.4.3). The muscle fibers or
muscle cells have a diameter of 0.01 to 0.1mm
and attain a length of 150 mm and more.
The main components of muscle cells are the myofibrils,
each of which has a diameter of 1–2 µm.
Up to 1000 myofibrils arranged parallel to each
other stretch through the muscle cell in the
direction of the fiber.
White muscle (birds, poultry), which has a high
ratio of myofibrils to sarcoplasm, contracts
rapidly but tires quickly. It can be distinguished
from red muscle, which is poor in myofibrils
but rich in sarcoplasm. Red muscles are used
for slow, long-lasting contractions and do not
tire quickly. Figure 12.3 shows a cross-section
of a muscle fiber with numerous myofibrils.
A greatly magnified, oblique view of a fiber of
this type is presented in Fig. 12.4 and Fig. 12.5
shows separated myofibrils.
The organization of the muscle contractile apparatus
is revealed in a longitudinal section of the
muscle fiber. The characteristic crossbondings
(“striations”; Fig. 12.6) of skeletal muscle are
due to the regularly overlapping anisotropic
A bands, which double refract polarized light,
and the isotropic I bands. The dark bands, the
Z line, are in the middle of the light I bands and
perpendicular to the axis of the fiber. The dark
A bands are crossed in the middle with light
H bands, while the dark M line is situated in the
middle of the H bands (Fig. 12.7). A single contractile
unit of a myofibril, called the sarcomere,
stretches from one Z line to the next and consists
of thick and thin filaments. Figure 12.8a shows