Qualification and quantification of fish protein in prepared surimi crabstick

Abstract

Species identification and protein quantification in surimi crabstick were achieved using sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE). When the Lowry and Kjeldahl protein determination methods were compared, the former showed more consistent results. Densitometric scanning of the gels was used for quantification of total fish protein as well as total egg white protein. The lower molecular weight proteins, 30 kDa and lower, proved to be the most useful in fish species identification as well as egg white protein addition. Using a combination of the myosin heavy chain band and the species-specific myosin light chain (Alaska pollock: 22.5 kDa; Pacific whiting: 24.4 kDa) proved the most accurate in calculating fish protein content of the crabstick sample, while for those samples that contained egg white, quantification was accomplished from the densitometric analysis of the overlapping bands of actin (45 kDa) from fish and ovalbumin from egg white. Lysozyme (14.3 kDa) proved to be a unique protein band in determining the presence of egg white when the content of dried egg white was equal to or exceeded 0.5% of the total weight of the final crabstick.