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Low and high pH treatments induce a molten globular structure in myosin which improves its gelation properties |
M. DAVENPORT and H. G. Kristinsson. Dept. of Food Science & Human Nutrition, Univ. of Florida, 359 FSHN Bldg., PO Box 110370, Gainesville, FL 32611-0370 A new process for muscle protein isolation utilizing high or low pH treatment followed by pH readjustment to neutral pH values produces a protein isolate of good functional properties. Myosin is the single most predominant protein in the protein isolates. The objective was to study how different high and low pH treatments affect the conformation and gelation properties of myosin. Myosin isolated from channel catfish muscle was used for this study. Myosin samples were treated to different low (2-3.5) pH and high (10.5-12) pH values at different ionic strengths (0-500 mM NaCl) followed by pH-readjustment to pH 6-7. Gelation properties of pH-treated vs. untreated myosin were compared at pH 6-8 in the presence or absence of NaCl in a rheometer employing oscillatory testing. Myosin conformational changes were determined by intrinsic tryptophan fluorescence, surface hydrophobicity (ANS binding) and circular dichroism. Myosin ATPase activity was also assayed. Low and high pH-treatment significantly improved myosin’s ability to form gels but led to a loss in ATPase activity. The mechanism of gel formation and final gel strength was highly dependent on what specific acid and alkali pH and ionic strength was used. Conformational studies indicated that myosin takes on different partly unfolded molten globular forms depending on what type of pH-treatment was used. These modified myosin structures with increased exposed hydrophobic groups are responsible for the improvements in gelation. Low and high pH-treatments lead to substantial changes in the conformation and gel forming ability of myosin that are specific to the pH and ionic strength used. By varying environmental conditions at low and high pH one can therefore obtain different myosin structures of modified functionality. Knowledge of the molecular changes of myosin at low and high pH may lead to development of muscle products with improved functional properties.
Session 42, Food Chemistry: Proteins II
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