Role of pH in solubility and conformational changes of pacific whiting muscle proteins

This study was conducted to better understand biochemical changes of fish muscle proteins as affected by novel surimi process, acid- or alkali-aided solubilization. At 10 mM NaCl, between pH 5 and 10, the solubility of Pacific whiting muscle proteins was low but increased dramatically as the pH was shifted to either acidic or alkaline pH. At 600 mM NaCl, the isoelectric point was shifted to the acidic direction by about 2 pH units, resulting in aggregation of proteins at low pH, but improving the solubility of MHC (myosin heavy chain) between pH 6 and 10. ANS surface hydrophobicity (ANS-S-o) showed much greater values than PRODAN surface hydrophobicity (PRODAN-S-o) for samples treated at pH 2 - 4 perhaps due to an enhancement of the electrostatic interactions between the ANS probe and proteins. At very high pH, according to hydrophobicity results, proteins were partially refolded when the ionic strength increased. Under acidic conditions, SDS-PAGE demonstrated the degradation of MHC at 10 mM NaCl. The formation of MHC polymers was observed under alkaline treatment with a concomitant decrease of SH content.