FAQ
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What are the general proteins of meat?
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Meat quality is profoundly impacted by the content of the different proteins within the meat. As noted, the three primary protein classes have historically been catagorized into the three or four major catagories. The characteristics and concentration of these proteins will impact the foods. Myofibrillar proteins are those which compose the contractile structure of the muscle. Thus, they function to translate chemical energy into the mechanical energy of the muscle. The primary types of proteins designated in this class are myosin (50-55 percent), actin (20-25 percent, tropomyosin (10-15 percent). Connective tissue proteins consist of collagen, elastin, reticulin and ground substance.
The other major classes as far as meat tenderness is concerned are the connective tissue. Connective tissues, of course, are made up of collagen, tropocollagen, elastin, the reticulum, and ground substances. This slide shows a diagram of collagen. In looking at this scanning electron micrograph of Jones' as shown in this slide, one can see the collagen on the surface of the muscle fiber. This slide summarizes again the different types of connective tissue.
The amount of collagen is important because as collagen increases the toughness of the meat generally increases. A number of factors influence the amount of connective tissue. one of these, is the age of the animal and the breed and species variety of the animal. Generally speaking, as the animal gets older, the collagen gets tougher. There becomes more intra- and inter-molecular of the collagen cross-bonding.
This aging influence on the intra- and inter-molecular structure of collage has created considerable confusion amount researchers. original research attempted to determine why meat was tough. They did feel that the amount of collaqen would influence toughness with more collagen meaning a tougher piece of meat. Using the Warner-Bratzler shear apparatus they sometimes found that age correlated and sometimes percentage collagen correlated and sometimes there appeared to be no relationship between shear values and collagen and toughness. Again, the higher the shear force values the tougher the piece of meat. For example, veal has a very high collagen content and is considered to be a tough muscle when analyzed with the Warner-Bratzler shear appartus. of course, if the veal is properly cooked it can be made to be tender. Veal has a high collaqen content because collagen covers every muscle fiber and all the muscle fibers possible for the steer are present in the veal. On a simple percentage/weight basis the collagen would be larger than in a larger animal where the fiber has increased in size and proportionally contains some of the other proteins. In studying this phenomena, researchers did observe that the collagen in veal is more susceptible to hydrolysis and solubilization than collagen in an older animal. Thus, measuring the amount of collagen by the traditional hydroxyproline test does not necessarily give the total picture of the tenderness and toughness of meat. An important piece of knowledge to meat researchers.
Very fortunately collagen makes up most of the muscle covering; however, elastin is connective tissue and is available and present in the animal. Elastin contributes to toughness and it's fortunate that it is in a minor portion of the animal. This is fortunate because it is not appreciably affected by heat and moisture, as collagen is so affected. Elastin, as shown in this diagram, has very organized structure. This organized structure is what some investigators attribute to the lack of much effect of heat and moisture.
Another major class of proteins are the saroplasmic p@oteins. This slide shows a piece of bright red cherry colored meat. This color is likely due to the sarcoplasmic proteins. In this instance, the myoglobin having formed oxymyoglobin. This diagram shows you the myoglobin. In this next diagram is shown the basic heme structure of myoglobin. This diagram shown is a shorthand way of presenting the pigments. myoglobin is present in the muscle and is a purplish-red color but, in the presence of oxygen, it becomes oxygenated and forms a bright red color called oxymyoglobin. Depending upon your point of view, myoglobin may become oxidized and form metmyoglobin. Metmyoglobin, as you see in this slide, is a brownish red color. It may occur due to freezing, salts, mild, ultraviolet light, high temperature, bacteria. There may be a denaturization of the globin. Oxymyoglobin is formed simply due to oxygenation of the iron in the heme; whereas metmyoglobin occurs due to oxidation of the iron. This slide shows you diagramatically some of these changes which occur in the pigments in the meat. This slide is showing the oxidation of myoglobin and oxymyoglobin and factors which accelerates it. In addition to the oxidation of myoglobin and oxygmyoglobin, there may be a breakdown of the pyrrole rings. The green colors or other unappetizing and disagreeable odors and colors formed are evidence of this breakdown.
Color in meat is important. In our fresh meat, generally speaking,the oxgmyoglobins are formed and evidence of freshness. In weiners consumers generally don't like the pale weiners, but rather want to have the nitroso-
globins or-hemoglobins or-myoglobins formed. These two slides show this. There's a nice formula in the book by Charley.
There are a number of other important proteins to the muscle and, either indirectly or directly, meat quality. This discussion will be developed at a later time.
A basic area of importance to meat quality are the changes which occur upon the slaughter of the animal for meat. Some of these changes are pre-rigor and some are post-rigor. Most of these changes influence not only the toughness and tenderness of the meat; but also the color and flavor. The most profound post-slaughter changes do influence meat texture. Some of these changes are chemical changes, physical changes and temperature changes. The chemical changes are very important from the standpoint of quality. They may be summarized, as shown in this slide, as changes in glycolysis, decrease in pH, decrease in creatine phosphate, decrease in ATP, and liberation of ammonia. The manner in which the changes affect the meat quality are many. For example, if one inhibits the decrease in pH by starving the animal or exercising it too much before slaughter a dark-cutting meat may result. The dark-cutting meat is very soft textured and black-purple in color. In pork, the effect of improper pH change is seen in the development of pale, soft extrudative tissue. This is a mushy soft tissue that will even show "water" leakage if a cut loin is left sitting on the table. The improper pH fall influences the water-holding capacity of the protein.
As an animal leaves rigor, some meat researchers indicate that the meat is now being aged. Most meat in this country is not really truly aged but is just allowed to pass through rigor and "slightly aged". Aging of meat will develop, generally speaking, a stronger, more pronounced flavor. It may be a more acceptable and tender piece of meat, depending upon the consumers personal preference.
This concludes a very superficial, quick, brief discussion of the basic components of meat. There is a slide tape lesson which briefly evaluates cooking methods and meat.
Updated: Wednesday, April 21, 2010. |
