Isolation and Characterization of Calpains From Rainbow Trout Muscle and Their Role in Texture Development

A single anion‐exchange column was used to resolve calpain I and II and their endogenous inhibitor, calpastatin, from the white muscle of rainbow trout ( Oncorhynchus mykiss ). Calcium requirement assays showed that calpain I and II required approximately 0.2 mM and 2.5 mM, respectively, for half maximal activities. Isolation of calpain I and calpastatin were confirmed by Western blot. Incubation of trout muscle for 12 h postmortem, in a buffer containing CaCl 2 , decreased ( P < 0.0001) shear force compared to samples incubated in a buffer containing EDTA. This effect indicates that softening of fish muscle can be accelerated by activation of calpains with exogenous calcium.