Experimental cookery

The plasma proteins undergo denaturation by heat, acids, and surface orientation. That the lactate ion affects the extent of denaturation and the resulting density of myosin and albumen has been mentioned in Chapter I. Still greater changes are brought about by heat when the meat is cooked. In meat not only myosin and myogen may be found, but also denatured myosin and denatured myogen. In cooked meats these proteins may be entirely denatured. Isoelectric point of muscle proteins. Smith gives the isoelectric point of myosin as pH 5.0-5.3 and that of myogen as pH 6.3. Burns has given the isoelectric point of myosin at pH 3.9 and that for the myoproteins at pH 4.5 and 5. Post-Mortem Changes in Meat Immediately after slaughter, changes occur in the muscle of an animal. These changes, like the changes in milk and eggs, can be retarded by method of handling and storage. They are brought about by enzymes and microorganisms, and by chemical and physical means which alter the struc- ture and chemical composition of the meat. Muscle in the living animal is (1) pliant, soft, gel-like, yet somewhat viscous. After slaughter the muscles pass from this state into a stiff or rigid one (2) known as rigor mortis, or muscle rigor. After some time 212 MEAT the muscles again become pliant. This stage (3) is known as the passing of rigor. With longer storage enzymes and chemical means bring about (4) more extensive changes which produce ripened meat. With bacterial action and still more extensive changes (5) incipient putrefaction occurs. The passage from one stage to another is gradual with no definite dividing zone and is accelerated at higher temperatures and retarded at lower ones. Meat may be cooked during any of these stages and heat denaturation causes characteristic changes which are part of the post-mortem changes. Means of retarding these changes will be considered before these changes are discussed. Meat cooked before the onset of rigor is said to be tender. But rigor develops quickly so that this period is short. Concerning the question of tenderness of meat before the onset of rigor, Dr. Trowbridge, who has had many years of experience in meat work, wrote the author, **I doubt if freshly killed meat is ever as tender as the same meat ripened." Preservation of meat. Freezing. Meat may be frozen and then stored at temperatures of —10° to — 15°F. In this way the post-mortem changes are nearly inhibited. Curing. Common salt is the basis of all cures or pickles. Although many modifications are used, the methods may be divided into two classes, brine and dry-salt cures. Salt not only preserves but tends to dry the meat. Sugar may be added for flavor. Sugar also tends to keep the muscles softer than when salt is used alcne and thus tends to increase the tenderness. When sugar is added to the brine, the process is known as ''sugar cure" or "sweet pickle." Saltpeter (potassium nitrate) or Chili saltpeter (sodium nitrate) or the nitrite salts of potassium and sodium may be used in cured meat. The red color of cured meat is due to the action of nitrite on the hemo- globin of the muscle. If only nitrate salts are used in the brine, they are reduced to nitrite by bacterial action. Cured meat may be smoked and partially dried on the surface. Actual smoke and not chemical treatment to produce a smoke flavor must be used in establishments under federal inspection.