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

Abstract

During surimi processing, the total cathepsins B+L+L-like activities in minced, leached and NaCl-ground meats were 2.45, 2.07 and 1.77 units/g, respectively. There was still 77% activity left even after 8 weeks storage at -20°C. High calpain and calpastatin activities in the crude enzymes from frozen mackerel surimi suggested that they were difficult to remove during processing and very stable during frozen storage. The SDS-PAGE analysis indicated that the optimal conditions for the hydrolysis of myosin heavy chain (MHC) were 40-55°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 purified cathepsins L and/or L-like decreased significantly (P<0.05) after 2 h incubation at 55°C. These results suggested that cathepsins L and L-like left in surimi had MHC-degrading ability which consequently caused gel softening during setting at 40-55°C.