3-5 |
Control of proteolysis in aquatic food products |
T. BORRESEN and H. H. Nielsen. Dept. of Seafood Research, Danish Institute for Fisheries Research, Bldg. 221, DTU, Lyngby, DK-2800, Denmark Enzymes indigenous to fish muscle will cause tissue degradation and softening of the fillet when the fish is stored after harvest in aquaculture facilities or in capture fisheries. The development is very temperature dependent, and fish from cold waters must be stored chilled in ice to avoid serious quality reductions. The proteolytic enzymes are of a type similar to what is found in muscle tissue from red meat. In contrast to enzymatic reactions for making red meat tender, the equivalent enzymatic action in fish tissue leads to unwanted softening in most species during storage. Some products are prepared where mild autolysis of the muscle tissue is desired. An example is gravad fish, where the filleted fish is slightly salted in a cold marinade under mild pressure for a day or two. In some cases, as e.g. heavily salting of herring, proteolysis is wanted for obtaining proper texture and taste, and a part of the fish intestines is left in the gut cavity in order to obtain the right enzymatic activity. In the presentation an overview will be given of the proteolytic processes that have been studied in this product, and some clues will be given as to how the proteolysis may be controlled. Temperature is an important parameter, and if heavily salted fish is stored at e.g. tropical temperature for several months, the entire fish tissue will be dissolved, thus leading to the product known as fish sauce. For crustaceans it is necessary to ripen e.g. the raw shrimp before peeling for a day or two in order for indigenous enzymes to loosen the connections between the muscle and the chitin shell. If left for too long before cooking and peeling, deaminases will lead to an elevated pH and reduced quality of the shrimps.
Session 3, Control of endogenous enzymes in foods: A practical approach
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