Experimental cookery

Incipient putrefaction. Much discussion has occurred concerning the presence of bacteria within muscle. Moran states that in freshly killed muscle there is usually a low bacterial count. Hoagland, McBryde, and Powick found that certain bacteria may normally be present in some carcasses of beef, but they possessed no pathological significance and did not multiply in proper cold-storage conditions. At low-storage tempera- tures, spoilage by bacteria is most prevalent at the surface of the meat. As has been indicated, growth is slow during rigor, for the acidity of the meat does not favor the development of microorganisms. But with in- creased storage of meat, the acidity of the meat is lessened or the alkalinity increases and ammonia is liberated. Of the different tests proposed for the detection of incipient putrefaction. Baker believes that the determination of ammonical nitrogen has been the most useful and the presence of 0.02-0.025 per cent indicates the beginning of putrefaction. Thus Baker suggests that, when the pH has risen to />H 6.2 the meat has undergone deterioration. Changes occurring in meat during storage. Changes due to enzymes. The lipolytic, amylolytic, and proteolytic enzymes act on fats, carbohydrates, and proteins, respectively. During life, these and other enzymes are concerned with the metabolic processes of the body. Enzyme changes are usually brought about more rapidly with higher temperatures. At very low temperatures the action may be very slow and different from that at higher temperatures owing to differenes in activity of different enzymes at different temperatures. Hoagland, McBryde, and Powick have reported that the external fat and kidney fat in beef stored just above the freezing point of the meat showed increased fatty acid con- tent and a corresponding deterioration of these fats. They found less change in the intramuscular fat, as it was protected from bacterial action, and changes in it were due to lipase enzymes. Oxidative changes in fats are of course greater in the surface fat. The surface fat in ripened meat often shows greater changes in flavor than interior fat. Amylolytic enzymes bring about the change of glycogen to lactic acid. These changes occur rather early in storage. Proteolytic enzymes bring about changes of the proteins to amino acids, thus increasing the amino nitrogen, or the non-protein nitrogen, or the soluble nitrogen products of the meat. Hoagland, McBryde, and Powick found that, in quarters of beef stored 14 to 177 days, the increase in amino nitrogen amounted to 3 to 7 per cent of the total nitrogen of the beef. Autolytic changes in beef at 31°. C. Hoagland, McBryde, and Powick stored pieces of beef free from bacteria in sterile containers at a tempera- ture of 37 °C. for periods of 7 to 100 days. Considerable juice exuded from the pieces of meat, which turned brown in color. The beef was also brown 218 MEAT