Acid-aided protein recovery from enzyme-rich Pacific whiting

Relatively higher protein recovery was obtained in acid-aided processing. Solubility was lowest at pH 5 and gradually increased up to pH 11.0. A sharp increase in solubility occurred at alkaline pH between 9.5 and 11.0 and at acidic pH between 3.0 and 1.5. Cathepsin B and L showed higher activities in acid surimi than conventional surimi. Acid-aided surimi did not show Ca- and Mg-ATPase activity and also had lower surface hydrophobicity and sulfurhydryl contents than conventional surimi. Acid processing resulted in low breaking force, possibly due to the activity of retained cathepsin L enzymes. Myosin heavy chain (MHC) and actin were degraded in acid processing and produced major bands right below MHC and actin.