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S. THAWORNCHINSOMBUT1, J. W. Park1, G. T. Meng2, and E. C. Y. Li-Chan2. (1) Dept. of Food Science & Technology, Oregon State Univ., OSU Seafood Research Lab., 2001 Marine Dr., Rm. 253, Astoria, OR 97103-3420, (2) Food, Nutrition & Health Program, Univ. of British Columbia, 6650 N.W. Marine Dr., Vancouver, BC V6T 1Z4, Canada Raman spectroscopy can be used advantageously to determine the molecular structure of food proteins in liquid or solid form. This technique yields information on secondary structure fractions, disulfide bond conformation, or the aromatic side chain environment. Due to the opaque or solid nature of many foods, changes in protein functionalities that cannot be differentiated by other methods are amenable to Raman spectroscopy. The objective of this study was to measure the stability of alkali-treated proteins and conventional surimi (CS) at various storage conditions using Raman spectroscopy. Alkali-treated proteins and CS were prepared from fresh Rockfish. Fish proteins were solubilized at pH 11 and subsequently recovered at pH 5.5. Two pH (5.5 and 7.0) were applied to this recovered pellet, which were further subdivided into 2 sets of cryoprotectants: 0% and 8% (sucrose:sorbitol=1:1), respectively. All treatments were subjected to 3 freeze-thaw cycles. One set of samples containing cryoprotectants was stored at –80°C without freeze/thaw. Before analysis, all samples were adjusted to maintain equal pH (7) and cryoprotectants. Gels were prepared at 78.5% moisture without salt, except for CS (2%). Fracture analysis and folding test were performed. No significant textural difference was noticed between samples stored at pH 5.5 and 7.0. Highest texture was found for samples frozen at pH 5.5 and 7 with cryoprotectants and CS, while lowest texture was observed for those frozen/thawed without cryoprotectants. Raman spectral analysis demonstrated that refolding of alkali-treated proteins by pH adjustment to 7.0 was achieved, but not completely. CS showed higher a–helix content (~50%) than alkali-treated proteins (~20-30%). Frozen storage induced a decrease and an increase in the a–helix of CS and alkali-treated samples, respectively. Alkali-treated proteins were slightly less stable than CS during frozen storage. Raman spectroscopy is a potential tool to study protein structural changes under various storage conditions.
Session 63, Aquatic Food Products: Quality, processing, antioxidants and surimi
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