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Effect of pH-Shift Processing and Surimi Processing on Atlantic Croaker (Micropogonias undulates) Muscle Proteins



ABSTRACT:  Extraction and recovery of fish muscle proteins with the pH-shift process was investigated for Atlantic croaker and compared to a laboratory scale surimi process. The acid-aided process led to higher recoveries (P < 0.05) than the alkali-aided process, which in turn led to higher recoveries (P < 0.05) than surimi processing. Lipid reductions were highest (P < 0.05) for the alkali-aided process, followed by the acid-aided process, with surimi giving the least reduction. No major differences in recovered proteins could be seen for the three processes, except both pH-shift processes had a protein band (∼150 KDa) possibly representing partial hydrolysis of myosin. Oscillatory rheology on protein pastes during heating and cooling showed the highest storage moduli for the alkali-aided isolate, followed by the acid aided isolates and surimi. Torsion testing on protein gels demonstrated significantly higher strain and stress values for gels made from frozen isolates with added cryoprotectants compared to fresh gels without added cryoprotectants. Gel stress was significantly higher (P < 0.05) for the frozen gels with added cryoprotectants made from the isolates, compared to surimi. Although isolate pastes had higher (P < 0.05) lightness values than surimi pastes, surimi gels had higher (P < 0.05) lightness than isolate gels. The acid-aided gels had higher levels of yellowness than the other treatments. Both surimi and alkali-aided isolates had significantly (P < 0.05) lower oxidation levels compared to the ground raw material. The acid isolate had poor oxidative stability and gave higher oxidation values than the raw material. Surimi and alkali-aided pastes and gels also had higher oxidative stability than acid-aided gels.