Why a meat that is well suited to boiling is not good for roasting.
MEAT IS AGREEABLE TO EAT ONLY WHEN it has been aged for a sufficient period of time. After an animal is slaughtered its meat begins to toughen (for twenty-four hours in the case of beef). This toughness can be reduced by as much as 80% by aging, which lasts for several days (ten in the case of beef). Can this period be shortened, or is it at least possible to determine the minimum amount of time needed to preserve carcass and muscle so that a given cut of meat will be properly tenderized? Ahmed Ouali and his colleagues at the Institut National de la Recherche Agronomique (INRA) station for meat research in Clermont-Ferrand analyzed the characteristics of muscle tissue in order to predict the length of time needed for aging different kinds of meat.
The first stage in the transformation of animal muscles into meat is the onset of cadaveric rigidity. Muscle cells continue to contract and relax immediately after death because they still contain adenosine 5’-triphosphate (ATP), a molecule that stores energy. The chemical cycles of muscle cells regenerate ATP for a certain time, but when it is produced only by the degradation of glycogen (which serves as a reserve supply of glucose) the muscle is no longer able to relax and remains in a contracted state.
During this phase the degradation of glycogen and glucose produces lactic acid, whereas the degradation of ATP releases phosphoric acid, with the result that the muscles are acidified. The swiftness of acidification depends chiefly on the type of muscle: Red (or slow-contracting) muscles, which derive their energy from oxygen carried by the blood, are acidified less and less quickly than white (or fast-contracting) muscles, which do not consume oxygen, making them more vulnerable to alteration by microorganisms.
Tenderizing and Degradation
The conditions under which cadaveric rigidity occurs determine the course of the next phase, tenderizing, which probably results from the degradation of structural elements. A distinction has long been made between the sort of toughness associated with collagen (the protein that sheathes muscle cells, grouping the muscle cells into bundles and the bundles into muscles) and the sort associated with myofibrils (the proteins responsible for the contraction of muscles). It has recently been observed that collagen, which is mostly unaffected by the tenderizing process, provides an index, or baseline, for measuring toughness. Collagen varies according to its concentration in muscles and determines the preferred cooking method for different cuts of meat. Pieces with high concentrations of collagen are best boiled, whereas ones with low concentrations of collagen are better suited to roasting.
Two types of mechanisms seem responsible for tenderizing myofibrils. Certain proteolytic enzymes decompose proteins, breaking down the filaments and fibrils, and an increase in osmotic pressure dissociates the constituent proteins of the filaments.
The INRA biochemists studied three groups of enzymes capable of degrading myofibrillar proteins: cathepsins, calpains, and a complex of proteins known as proteosomes, less well known than the other two because it has only recently been discovered. The activity of these enzymes in muscles depends on acidity, the concentration of calcium ions and ATP, and so on. In living animals it is limited by various inhibitors that prevent the decomposition of muscles, but enzymatic regulation is suppressed after slaughter, largely as a consequence of acidification. Furthermore, the increase in the osmotic pressure of muscle cells that occurs after death facilitates and reinforces the action of the enzymes: The accumulation of small molecules and free salts in the intracellular liquid dissociates the protein complexes, permitting the proteolytic enzymes to penetrate to their substrates more easily.
The sensitivity of myofibrils to proteolytic enzymes greatly varies according to the type of muscle. The myofibrils in red muscle, for example, differ greatly from the ones in white muscle. These differences have to do not only with the identity of the myofibrillar proteins but also with the structure and extension properties of the myofibrils themselves: The more rapidly the muscles contract, the more rapid their enzymatic alteration. This observation explains, at least in part, the well-known relationship between the age of cattle at the time of slaughter and the tenderness of their meat after aging. The aging time ranges from 4–5 days for calves to 8–10 days for steers because the muscles of the older animals are redder than those of the younger ones.
Understanding these mechanisms will allow government researchers and commercial food technologists to concern themselves with the tenderness and, more generally, the quality of meat and to incorporate these properties in the criteria they apply, which today are geared mainly to shortening the time needed for animals to reach maturity. One of the chief objections to this practice is that the very white meat of animals subjected to artificially accelerated growth is also less flavorful and less juicy than the meat of animals from the same breed that have been raised by traditional methods. What is needed above all is patience.