2009_Book_FoodChemistry

594 12 Meat
Table 12.16. Average composition of some internal organs
and blood (g/100 g edible portion)
Mois-
Carbo- Caloric
Organ ture Protein Fat hydrate value (kJ)
Heart
beef 75.5 16.8 6.0 0.56 517
pork 76.8 16.9 2.6 0.4 390
Kidney
beef 76.1 16.6 5.1 – 471
pork 76.3 16.5 3.8 0.80 435
Liver
beef 69.9 19.7 3.1 5.90 550
pork 71.8 20.1 4.9 1.14 542
Spleen
beef 76.7 18.5 2.9 422
pork 77.4 17.2 3.6 – 426
Tongue, beef 66.8 16.0 15.9 0.4 867
Lung, pork 79.1 13.5 6.7 – 477
Brain, veal 80.4 9.8 7.6 0.8 461
Thymus, veal 77.7 17.2 3.4 – 418
Blood
beef 80.5 17.8 0.13 0.065 309
pork 79.2 18.5 0.11 0.06 319
sitions of some variety meats are shown in Table
12.16.
Intestines, with their high content of elastin, make
excellent natural sausage casings. These and beef
stomach are specialty dishes.
Pork skin is an ingredient of jellied meat and
blood sausage. It is also consumed directly and
is a good source of vitamin D. Cartilage and
bones contain tendons and ligaments which are
collagen- and elastin-type proteins. Cartilage and
bones are similar in composition, with the exception
of their mineral content; the former contains
1% minerals and the later averages 22% minerals,
ranging from 20–70%. The fat content of bones
can be as high as 30% and commonly varies between
10–25%. Spinal cord and ribs, when boiled
in water, release gelatin-type substances and fat
and, therefore, both are used in soup preparations
(bouillon, clear broth or bouillon cubes or concentrated
stock).
12.6.1.10 Blood
The blood which drains from a slaughtered animal
is, on the average, about 3–4% of the live
weight (oxen, cows, calves) but is particularly
high for horses (9.98%) and low for hogs (3.3%).
Blood has been used since ancient times for making
blood and red sausages and other food products.
Blood consists of protein-rich plasma in which
the cells or corpuscles are suspended. They are
the red and white blood cells (erythrocytes and
leucocytes, respectively) and the platelets (thrombocytes).
The red blood cells do not have nuclei
and are flexible round or elliptical discs with indented
centers. The diameters of red blood cells
vary(inµm:4ingoat;6inpig;10inwhale;and
up to 50 or more in birds, amphibians, reptiles
and fish). Red blood cells contain hemoglobin,
the red blood pigment. White blood cells contain
nuclei but no pigments, are surrounded by membranes,
are 4–14 µm in diameter and are fewer in
number than red blood cells. In addition to salts
(potassium phosphate, sodium chloride and lesser
amounts of Ca-, Mg- and Fe-salts), various proteins,
such as albumins, globulins and fibrinogen,
are present in blood.
The N-containing low molecular weight substances
(“residual nitrogen”) of blood comprise
primarily urea and lesser amounts of amino
acids, uric acid, creatine and creatinine. During
coagulation or clotting of blood, the soluble
fibrinogen in the plasma is converted to insoluble
fibrin fibers which separate as a clot. Coagulation
is a complex reaction catalyzed by the enzyme
thrombin, the precursor of which is prothrombin.
Thrombin reacts with fibrinogen to form insoluble
fibrin. The mesh of long fibrin fibers traps
and holds blood cells (platelets, erythrocytes and
leucocytes). Hence, the clot is colored red. The
remaining fluid, which contains albumins and
globulins, is the serum. Blood plasma contains
0.3–0.4% fibrinogen and 6.5–8.5% albumin plus
globulin in the ratio of 2.9:2.0.
The composition of blood is given in Table 12.16.
Blood clotting requires the presence of Ca 2+
ions. Hence, Ca 2+ -binding agents, such as
citrate, phosphate, oxalate and fluoride, prevent
blood coagulation. In the processing of blood
into food, coagulation is occasionally retarded
by stirring the blood with metal rods onto which
the fibrin deposits. Currently, blood clotting
is inhibited by using Ca 2+ -complexing salts.
After centrifugation, blood stabilized in this way
yields about 70% of plasma containing 7–8%