Food Chemistry

568 12 Meat

Fig. 12.6.A longitudinal section of two adjacent mus-
cle fibers. (fromSchultzandAnglemier, 1964)

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 in-
testinal tract. Smooth muscle fibers are useful in
the examination of meat products; preferentially
for the detection of pharynx (esophagus), stom-
ach or calf pluck (heart, liver and lungs).

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

Muscle proteins can be divided into three large

groups (cf. Table 12.5):

• Proteins of the contractile apparatus, ex-
  tractable with concentrated salt solutions
  (actomyosin, together with tropomyosin and
  troponin).


• Proteins soluble in water or dilute salt solu-
  tions (myoglobin and enzymes).


• Insoluble proteins (connective tissue and
  membrane proteins).

12.3.2.1 Proteins of the Contractile

Apparatus and Their Functions

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