Nitrogenous extractives. Muscle tissue contains end products of
protein metabolism. These are removed as they accumulate during life
from the tissues by the body fluids and are excreted through the kidneys.
Creatine and creatinine are found in the muscles and to a lesser extent
in the blood. Uric acid and other nitrogenous extractives are also found in
the muscles. They are of interest in meat cookery, because they are the
source of part of the distinctive flavor of meat, and stimulate the flow of
gastric juice.
Carbohydrates and fats. The carbohydrate found in the muscle tissue
is glycogen.
Burns states "the fat content of the cell is unique. Every cell has a
fairly constant content of lipide, although when stained by the usual
methods to demonstrate fat, no evidence is given of such a content. This
masked fat is only made visible when the cell is diseased or disintegrated."
The proteins of the muscle fibers. The proteins of the muscles are
composed largely of two types : ( 1 ) the structural proteins, which consist
largely of collagen awd elastin and (2) the protoplasmic proteins, variously
called myosinogen, myogen, myosin, and myoglobulin. The two types of
proteins behave differently when heated, the effect of heat on the structural
or connective tissue proteins having been considered. The proteins of the
plasma are soluble in certain concentrations of salt solutions, such as
sodium chloride, sodium sulfate, magnesium sulfate, ammonium sulfate,
sodium phosphate, and other salts. Hence, they are often referred to as
the soluble proteins.
The entity of the meat proteins is in the same status as that of flour
POST-MORTEM CHANGES IN MEAT 211
and other food proteins. (See proteins of flour, Chapter XL) They may
or may not be a mixture of proteins having similar properties.
The soluble muscle proteins are most commonly designated as myosin
and myogen. They are classified as globulins, the myosin being completely
precipitated and the myogen partially precipitated by saturated magnesium
sulfate. However, complete information about these proteins is lacking.
Moran quotes Muralt as suggesting that the fibrils are composed of a
firmer material (myosin) surrounded by the more liquid or gel-like
myogen (sarcoplasm). The evidence for this w^as based on X-ray studies,
but is not generally accepted. Since myogen is doubly refractive, this is
almost conclusive proof that it occupies the light bands in the muscle fibers.
Characteristics of proteins. One of the outstanding characteristics is
the extent to which solubility is affected by small changes in salt concen-
trations. Smith has reported that exhaustive extraction with any given
salt yields only a fraction of the total protein. The highest yield, about
90 per cent, was obtained with 1.87 M NH4CI, followed by 1.65 M
LiCl, and a still lower percentage with the other salts tried. Howe found
that the total globulins (myosin and myogen) compose about one-third of
the total protein of the muscle, and that the insoluble protein composes
approximately one-half of the total protein of the muscles of the cow,
calf, and rabbit. In addition to variation with concentration, with the
number of extractions, and with different salts, the solubility varies with
pH. In general the proteins are less soluble at the isoelectric point.
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Nitrogenous extractives. Muscle tissue contains end products of
protein metabolism. These are removed as they accumulate during life
from the tissues by the body fluids and are excreted through the kidneys.
Creatine and creatinine are found in the muscles and to a lesser extent
in the blood. Uric acid and other nitrogenous extractives are also found in
the muscles. They are of interest in meat cookery, because they are the
source of part of the distinctive flavor of meat, and stimulate the flow of
gastric juice.
Carbohydrates and fats. The carbohydrate found in the muscle tissue
is glycogen.
Burns states "the fat content of the cell is unique. Every cell has a
fairly constant content of lipide, although when stained by the usual
methods to demonstrate fat, no evidence is given of such a content. This
masked fat is only made visible when the cell is diseased or disintegrated."
The proteins of the muscle fibers. The proteins of the muscles are
composed largely of two types : ( 1 ) the structural proteins, which consist
largely of collagen awd elastin and (2) the protoplasmic proteins, variously
called myosinogen, myogen, myosin, and myoglobulin. The two types of
proteins behave differently when heated, the effect of heat on the structural
or connective tissue proteins having been considered. The proteins of the
plasma are soluble in certain concentrations of salt solutions, such as
sodium chloride, sodium sulfate, magnesium sulfate, ammonium sulfate,
sodium phosphate, and other salts. Hence, they are often referred to as
the soluble proteins.
The entity of the meat proteins is in the same status as that of flour
POST-MORTEM CHANGES IN MEAT 211
and other food proteins. (See proteins of flour, Chapter XL) They may
or may not be a mixture of proteins having similar properties.
The soluble muscle proteins are most commonly designated as myosin
and myogen. They are classified as globulins, the myosin being completely
precipitated and the myogen partially precipitated by saturated magnesium
sulfate. However, complete information about these proteins is lacking.
Moran quotes Muralt as suggesting that the fibrils are composed of a
firmer material (myosin) surrounded by the more liquid or gel-like
myogen (sarcoplasm). The evidence for this w^as based on X-ray studies,
but is not generally accepted. Since myogen is doubly refractive, this is
almost conclusive proof that it occupies the light bands in the muscle fibers.
Characteristics of proteins. One of the outstanding characteristics is
the extent to which solubility is affected by small changes in salt concen-
trations. Smith has reported that exhaustive extraction with any given
salt yields only a fraction of the total protein. The highest yield, about
90 per cent, was obtained with 1.87 M NH4CI, followed by 1.65 M
LiCl, and a still lower percentage with the other salts tried. Howe found
that the total globulins (myosin and myogen) compose about one-third of
the total protein of the muscle, and that the insoluble protein composes
approximately one-half of the total protein of the muscles of the cow,
calf, and rabbit. In addition to variation with concentration, with the
number of extractions, and with different salts, the solubility varies with
pH. In general the proteins are less soluble at the isoelectric point.