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J. W. PARK1, Y. J. Choi2, J. Yongsawatdigul3, Y. S. Kim1, and S. Thawornchinsombut1. (1) Dept. of Food Science & Technology, Oregon State Univ., OSU Seafood Research Lab., 2001 Marine Dr., Rm. 253, Astoria, OR 97103-3420, (2) Div. of Marine Bioscience, Gyeongsang National Univ., 445 Inpyeong Dong, Tong Yeong, 650-160, South Korea, (3) Institute of Agricultural Technology, Suranaree Univ. of Technology, School of Food Technology, 111 University Ave., Nakhon Ratchasima, 30000, Thailand Conventional surimi processing is aimed to concentrate myofibrillar proteins by removing sarcoplasmic proteins through continuous washing of the fish mince. The process consumes a tremendous amount of water and typically results in yields as low as 20-30%. As the pH is shifted away from the isoelectric point, proteins become negatively or positively charged, resulting in increased solubilization and solubility. The removal of stroma proteins and lipids, including membrane lipid, using centrifuge results in a significantly higher yield. Objectives were to investigate the biochemical and functional properties of fish proteins isolated from enzyme-laden Pacific whiting and enzyme-free rockfish as coldwater species and further identify conformational changes of proteins. SDS-PAGE revealed that Pacific whiting fish proteins were highly degraded by acid or alkali treatment. The highest breaking force of gels was measured for fish proteins treated at pH 11, while high deformation values were obtained at pH 2 and 11. Strong cathepsin L-like activity was found in fish proteins treated at pH 10.5 corresponding well with lower breaking force and deformation values. Acidic and alkaline solubilization followed by isoelectric precipitation induced degradation of myosin heavy chain from rockfish muscle, resulting in a protein band of @ 120 kDa. Both myofibrillar and sarcoplasmic proteins underwent denaturation after acidic and alkaline treatment, exhibiting minimal solubility and absence of endothermic peaks. Acid and alkali-treated muscle proteins readily aggregated upon heating, showing different dynamic rheological patterns as compared to whole muscle and washed mince. Disulfide linkages occurred at a greater extent in gel prepared by alkaline solubilization, resulting in higher breaking force and deformation. Raman spectral analysis demonstrated that refolding of alkali-treated proteins was achieved, but not completely. Conventional surimi contained higher a helix than the pH-shifted proteins. Frozen storage induced a decrease in the a helix of conventional surimi but an increase in alkali-treated proteins.
Session 3, Fish protein recovery using pH shifts
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