40-4 |
Characteristics of sarcoplasmic proteins at various pH and their interaction with myofibrillar proteins |
Y. S. KIM and J. W. Park. Dept. of Food Science & Technology, Oregon State Univ., Astoria Seafood Lab., 2001 Marine Dr., Rm. 253, Astoria, OR 97103-3420 Fish muscle protein is composed of 20-40% sarcoplasmic proteins (SP) depending on species. New surimi processing methods, acid- or alkali-aided, have significant advantages over conventional processing; primarily extremely high yields (35-40%) since nearly all myofibrillar and sarcoplasmic proteins are solubilized before centrifugal separation. While the conventional process removes SP through washing and dewatering, the new pH-driven process retains SP in the system. The roles of SP in the gelation of fish proteins, however, regardless of the processing conditions, have not been fully explored. Our objectives were 1) to investigate the influence of pH and salt on sarcoplasmic proteins from rockfish, and 2) to determine the effects of sarcoplasmic proteins in a gel matrix of myofiblillar proteins. Rockfish fillets were homogenized in deionized water with a 1:1 mixing ratio. The homogenate was then centrifuged. The resulting supernatant (sarcoplasmic proteins) was subjected to freeze-drying. Freeze-dried sarcoplasmic powder was used for various physicochemical measurements: protein solubility, protein loss, DSC, and SDS-PAGE. The interaction between SP and Alaska pollock surimi (myofibrillar proteins) was also evaluated measuring oscillatory dynamic properties, DSC, SDS-PAGE, gel color, and gel texture. Solubility of SP was significantly suppressed at acidic pH conditions (pH 2-4) plus high salt concentration (0.5 M NaCl). This was also supported by SDS-PAGE results exhibiting extensively degraded SP. DSC results revealed SP gave three endothermic transitions. The loss of SP during the pH-driven process was the least at pH 2 and 3 followed by precipitation at pH 5.5. SP did not enhance the gelation properties of myofiblillar proteins, but positively contributed to gelation with myofiblillar proteins when compared to the treatment with sucrose replacing SP. The pH 2 and 3 treatments to solubilize the muscle proteins are likely to give the highest protein yield because of the minimum loss of SP.
Session 40, Aquatic Food Products: Surimi and proteins
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