2009_Book_FoodChemistry

568 12 Meat
12.3 Muscle Tissue: Composition
and Function
12.3.1 Overview
Muscles freed from adhering fat contain on the
average 76% moisture, 21.5% N-substances,
1.5% lipids and 1% minerals. In addition,
variable amounts of carbohydrates (0.05–0.2%)
are present. Table 12.4 provides data on the
average composition of some cuts of beef, pork
and chicken.
12.3.2 Proteins
Fig. 12.6. A longitudinal section of two adjacent muscle
fibers. (from Schultz and Anglemier, 1964)
Muscle proteins can be divided into three large
groups (cf. Table 12.5):
• Proteins of the contractile apparatus, extractable
with concentrated salt solutions
(actomyosin, together with tropomyosin and
troponin).
• Proteins soluble in water or dilute salt solutions
(myoglobin and enzymes).
• Insoluble proteins (connective tissue and
membrane proteins).
12.3.2.1 Proteins of the Contractile
Apparatus and Their Functions
Fig. 12.7. A longitudinal section of a sarcomere. (from
Schultz, Anglemier, 1964)
ations. Smooth muscles occur in mucous linings,
the spleen, lymphatic glands, epidermis and intestinal
tract. Smooth muscle fibers are useful in
the examination of meat products; preferentially
for the detection of pharynx (esophagus), stomach
or calf pluck (heart, liver and lungs).
About 20 different myofibrillar proteins are
known. Myosin, actin and titin quantitatively
predominate, acounting for 65–70% of the
total protein. The remaining proteins are the
tropomyosins and troponins, which are important
for contraction, and various cytoskeletal proteins,
which are involved in the stabilization of the
sarcomere.
12.3.2.1.1 Myosin
Myosin molecules form the thick filaments and
make up about 50% of the total proteins present in
the contractile apparatus. Myosin can be isolated
from muscle tissue with a high ionic strength
buffer, for example, 0.3mol/lKC1/0.15 mol/l
phosphate buffer, pH 6.5. The molecular weight
of myosin is approx. 500 kdal. Myosin consists