Enzyme freeze-thaw damage

Figure 3. Temperature zone of freeze-thaw damage to catalase. Half-milliliter aliquots of the enzyme (1.7 fig/ml) were frozen at 900°C/min without seeding...

The importance of muscle lysosomal enzymes to the food scientist stems from their apparent involvement in the aging of meats. For example, lysosomal cathepsins are possibly involved in the proteolytic degradation of muscle proteins (31). Lysosomal enzymes exhibit latency that is, they are retained in the lysosomal particle and released only when the particle membrane is damaged. In this regard the lysosomal enzymes are liberated and activated when the particle membranes are weakened by the postmortem drop in pH. Also, lysosomes are very subject to cryoinjury (72), and freezing and thawing of tissues such as muscle releases lysosomal enzymes resulting in autolysis. 

Such membrane damage has been observed by freezing and thawing of tissue, for example, of muscle tissue, in which the isoenzymes of glutamate oxalacetate transaminase (GOT) bound to mitochondrial membranes are partially released and found in the sarcoplasm. The pressed sap collected from fresh unfroze meat has only sarcoplasm enzymes, while the frozen and thawed meat has, in addition, the isoenzymes derived from mitochondria. The GOT isoenzymes can be separated by electrophoresis (Fig. 12.41). This procedure is also apphcable to fish. 

The enzyme is remarkably stable on storage, although repeated freezing and thawing can damage activity. 

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