83A-22 |
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S. THAWORNCHINSOMBUT and J. W. Park. Dept. of Food Science & Technology, Oregon State Univ., OSU Seafood Research Lab., 2001 Marine Dr., Rm. 253, Astoria, OR 97103-3420 A novel process for fish proteins has been intensely investigated to improve gelation properties and yield using pH-shifted treatment for surimi manufacture. During the last 3-4 years, our laboratory has done extensive work regarding maximizing the functionality and recovery yield of Pacific whiting (PW) proteins. Few studies, however, have examined the combined effect of pH and ionic strength (IS) on gelation characteristics of fish proteins using this novel pH-shift process. Our objective was to investigate the interactive effect of pH and IS on the biochemical and gelation properties of PW proteins compared to conventional surimi (CS). Twice-washed mince was adjusted to specific pH and IS conditions (pH 3, and 11 with IS 10, 150, and 400 mM NaCl). Precipitates were collected at pH 5.5 for fish proteins treated at both pH levels, and IS 10 and 150 mM, respectively. All samples treated at IS 400 mM were recovered at pH 4.5 due to the pI shifting caused by high IS. All gels were prepared at pH 7 without adding salt except CS. Gelation characteristics were elucidated by surface hydrophobicity (So), total SH content, SDS-PAGE, thermodynamic properties (DSC), and texture properties (Texture Analyser). The strongest gels were obtained from sample pH11/IS150 and CS. So and DSC thermograms demonstrated that, in addition to pH, adding salt during protein solubilization and subsequent recovery led to protein denaturation. Adjusting pH to 11 and/or adding salt during the surimi process promoted disulfide bonds as evidenced by a decrease in SH content and SDS-PAGE. Protein aggregation at the pI probably enhanced the strength of disulfide bonds in protein polymers, resulting in less gel elasticity. Results demonstrated that solubilized fish proteins at pH 3 or 11 could be refolded at pH 7. Nevertheless, strong gel was achieved only at limited ranges of IS.
Session 83A, Aquatic Food Products: Byproducts, mince and surimi
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