Enzymes are found in living systems; they are produced by the living cell; no living thing can exist without them; yet enzymes themselves are not living. It seems likely from evidence at hand that a majority of all the chemical reactions which occur in organisms are enzyme-controlled.
Now we come to the enzymes which are of specific importance to the meat industry. I will essentially mention three groups, the glycolytic, the proteolytic, and the fat hydrolyzing enzymes, although there are many more we could discuss.
The glycolytic process involved in slaughtered muscle tissue is of great importance to the meat industry. After slaughter the carcass is dressed and chilled during which process there is a solidification of fat and simultaneous development of rigor mortis, accompanied with the formation of lactic acid and other acids from tissue glycogen. The conversion of muscle glycogen through a sequence of enzymic reactions to form lactic acid in muscle tissue is called anaerobic glycolysis. The actual sequence of reactions involves numerous glycolytic enzymes.
There are essentialy about 30-some reactions involved in the reaction but this is the overall picture where we have glycogeyn plus 3ADP plus 3 phosphate plus H20-,22 lactic acid plus 3ATP.
One of the chief factors involved in glycolysis in meat is the production of lactic acid with a concomitant decrease in pH. nom1 living muscle tissue is approximately 7.2 to 7.4, but after rigor mortis, the pH drops to approximately 5.8. The chief asset of lowered pH in meat is its ability to restrain the growth of certain bacteria. Another factor which is of importance is that at a lowered pH the activity of proteolytic enzymes associated with tenderizing during the process of aging is enhanced. Some workers feel that g3ycolysis and, therefore, the lowered pH, direct& affects the color and texture of meat. indicates that such tissue is often depleted of muscle sugar and, therefore, the amount of lactic acid produced is decreased with a concomitant higher pH than in normal beef. The sticky condition of dark cutting beef has been considered by some to be associated with the relatively high pH. Whether the dark color and sticlqr texture is a direct effect of a higher pH is questionable.
The second group of significant meat enzymes is the proteolytic enzymes. The fact that meat undergoes physical and chemical changes during storage has long been noted. The process of aging meat, which has been practiced for many years has, in general, directly affected the tenderness qualities of meat.
Aging of meat is the process by which the meat is held at temperatures higher than normal for specified periods of time to enhance the quality of tenderness. It has been suggested that the tenderizing effect of aging is brought about by the action of naturally occurring proteolytic enzymes in muscle tissue. Very little is known about these natural entkties which de grade the protein molecule into smaller units. At the preserrt time, studies are in progress which may lead to the identification and characterization of these enzyme systems in muscle tissue. The information obtained through these studies may suggest new approaches to the problem of meat tenderization.
Proteolytic enzymes from other sources, such as glandular tissues, bacteria, fungi, and plants have been added to meat as a means of tenderizing and have gained much popularity. It should be mentioned that artificial tenderizers do not, at the present, indicate completely efficient tenderizing action in practical application, since many problems, including those associated with penetration of the tenderizers, uniform action, and flavor changes still have much to be desired.
The third group of significant meat enzymes is the fat hydrolyzing enzymes.
The fat splitting enzymes in meat are probably more of a detriment than an asset. Lipases hydrolyze fats to form free fatty acids and glycerol. If meat is stored without some control over the lipolytic enzymes the fats will be considerably altered. The free fatty acids will increase progressively on storage and, depending upon the product, the change may or may not be considered spoilage. For example, we may tolerate a considerable amount of free fatty acid in summer sausage while a similar amount in fresh meat would be considered a sign of spoilage. The lipolytic process can be slowed down considerably by chilling the carcass during storage.