Proteolysis consists of the progressive degradation and breakdown of major meat proteins (sarcoplasmic and myofibrillar proteins) and the subsequent generation of peptides and free amino acids. The result is a weakening of the myofibrillar network and generation of taste compounds; but its extent depends on many factors. One of the most important is the activity of endogenous muscle enzymes, which depends on the original crossbreeds (7,26) and the age of the pigs (9,10). Main muscle enzymes involved in these phenomena and their main properties are listed in Table 2. These enzymes show a great stability in long dry-curing processes like hams (15,27). Other important factors are related to the processing technology: for instance, the temperature and time of ripening will determine the major or minor action of the enzymes, and the amount of added salt, which is a known inhibitor of cathepsins and other proteases, will also regulate the enzyme action (28-31). Excessive softness in ham has been correlated with high cathepsin B activity and low salt content (32,33).
Great amounts of small peptides, in the range of 2700 to 4500 Da or even below 2700 Da, are generated during the process (34-36) although this generation may be depressed by the level of salt that inhibits muscle peptidases (37). Some of these peptides give characteristic tastes (34). Recently, several tri- and dipeptides have been isolated and sequenced (38). Final generation of free amino acids by endogenous muscle aminopeptidases is very important, reaching impressive amounts as high as several hundreds of milligrams per 100 g of ham (39-42).
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