Meat proteins collagen

In contrast to milk, where samples are primarily derived from cows, meat analysis has to be performed in samples of a widely different animal origin including cattle, lamb, swine, poultry, and fish. Muscle is a complex matrix with a pH of 5.7, composed of muscle fibers, various types of connective tissue, adipose tissue, cartilage, and bones. Sarcoplasmic proteins such as myoglobin, and glycolytic enzymes are soluble in water while the myofibrillar proteins such as myosin and actin are soluble in concentrated salt solutions (14). The connective tissue proteins, collagen and elastin, are insoluble in both solvents. 

In humans, the meat protein of the diet usually controls the isotopic composition of bone collagen, while carbohydrates from plant foods usually control the isotopic composition of apatite Our models indicate that reconstruction of diets from isotopic analyses of bone cannot be accomplished solely by the use of the collagen fraction The use of both collagen and hydroxyapatite phases of bone allows differentiation between energy and growth components of the diet, and therefore gives a considerable amount of detailed information about the total diet ... 

Meat proteins include sarcoplasmic, myofibrillar, and connective tissue proteins. Among the sarcoplasmic proteins are heme pigments and enzymes, which influence the color, smell, and structure of meat. Myofibrillar proteins and collagen are able to retain and hold water in meat structure and to emulsify fat. Therefore they influence the rheological properties of meat products. 

Basically, there are three major groups of proteins in muscle tissue (a) the sarcoplasmic proteins of the muscle cell cytoplasm, (b) the myofibrillar proteins, soluble at high ionic strengths, that make up the myofibril or contractile part of the muscle, and (c) the stromal proteins comprised largely of the connective tissue proteins, collagen, and elastin. The myofibrillar proteins and the stromal proteins are fibrous and elongated they form viscous solutions with large shear resistance. These properties coupled with other lines of indirect evidence indicate that the physical properties of the myofibrillar and stromal proteins are directly related to the texture and tenderness of meat (34). 

Another method still being tested is based on drastic treatment (heating to 130 °C at pH 9) of a meat sample. Under these conditions, extraneous proteins, collagen and blood plasma proteins solubilize, while the residual protein is calculated as MPDCP using a constant factor. 

Carnivores rely on a protein-rich diet and produce new biomass primarily from dietary amino acids, although the enzymes required for de novo amino acid synthesis are present (Garmes et al., 1998). Bone collagen, muscle (meat) and apatite were analyzed for a set of modern southern African herbivores and carnivores (Lee-Thorp et al., 1989). The isotopic analyses showed i C enrichment in bone collagen, apatite and muscle, and depletion in lipids. Difference in values between herbivores and carnivores indicates a trophic effect, which for carbon in bone collagen is 2.5-3%o (Fig. 2). 

Nowadays, ACE inhibitory peptides have been isolated from meat, remaining muscle proteins, skin collagen and gelatin, bone, and internal organs of fishes such as Alaska pollack, bonito, tuna, salmon, shark, and sardine. Table 16.1 provides a partial summary of ACE inhibitory peptides derived from marine fish sources, their amino acid sequence, the enzyme used for hydrolysis, and IC50 values. The IC50 value is the concentration of peptide that inhibits 50% of ACE activity. 

Proteins from animal sources Proteins from animal sources (meat, poultry, milk, fish) have a high quality because they contain all the essential amino acids in proportions similar to those required for synthesis of human tissue proteins (Figure 27.18). [Note Gelatin prepared from animal collagen is an exception it has a low biologic value as a result of deficiencies in several essential amino acids.]... 

The amount of stroma proteins is less in fish muscles (3-5%) than it is In beef or rabbit muscles (15-18%). This may explain why raw fish fillets are acceptable in Japanese dishes, whereas beef, rabbit and pork are rarely served raw. According to Fennema et al. (9.), tenderness is primarily related to collagen content, while toughness and water-holding capacity are associated with the myofibrillar proteins. Many papers on cooked meat mention both tenderness and toughness, while those on cooked fish note the problems of toughness rather than tenderness. This also might be related to the difference in content of the stroma proteins. 

Rubidium typically exists in the human body at the level of only 1/1,000 of 1 percent, and cesium content is even lower. Rubidium and cesium are both absorbed from soil by plants and are, therefore, present in small quantities in vegetables and up the food chain to meat products and humans. Rubidium is known to stimulate mammalian metabolism, probably because of its physical and chemical similarity to potassium, which plays a crucial role in electrical pulse transmission along nerve fibers protein synthesis acid-base balance and formation of collagen, elastin, and muscle. Its likeness to potassium may be the reason rubidium enhances growth in some plants. For particular insects, however, the introduction in the laboratory of rubidium to the bloodstream has been shown to drastically reduce fluid secretion and to change the electric potential across cell membranes. Excess rubidium is almost never encountered, however, in nature. 

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