Effects of mackerel cathepsins L and L-like, and calpain on the degradation of mackerel surimi

During surimi processing, the total cathepsins B+L+L-like activities in min ced, leached and NaCl-ground meats were 2.45, 2.07 and 1.77 units/g, respec tively. There was still 77% activity left even after 8 weeks storage at -20 degrees C. High calpain and calpastatin activities In the crude enzymes fr om frozen mackerel surimi suggested that they were difficult to remove duri ng processing and very stable during frozen storage. The SDS-PAGE analysis indicated that the optimal conditions for the hydrolysis of myosin heavy ch ain (MHC) were 40-55 degrees C, pH 5.5-7.0 for cathepsins L and L-like and pH 7.0-7.5 for calpain. The gel strength of surimi treated with calpain did not decrease significantly, but the strength of those treated with purifie d cathepsins L and/or L-like decreased significantly (P<0.05) after 2h incu bation at 55 degrees C. These results suggested that cathepsins L and L-lik e left in surimi had MHC-degrading ability which consequently caused gel so ftening during setting at 40-55 degrees C.