17E-13 |
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Y. LIANG and H. G. Kristinsson. Dept. of Food Science & Human Nutrition, Univ. of Florida, 130-B Aquatic Foods Pilot Plant, PO Box 110370, Gainesville, FL 32611-0370 The functionality of proteins may be improved by modification of their structures. Partial modification of the structure of egg white proteins by different acid and alkali unfolding and refolding may increase their hydrophobicity and flexibility and result in improved foaming properties. The objective was to study the effect of pH-induced unfolding and refolding of egg white proteins on their foaming properties and conformation. Egg white proteins were unfolded at either low pH (1.5, 2.5 and 3.5) or high pH (10.5, 11.5 and 12.5) and then refolded by adjusting the pH back to 4.5, 5.5, 6.5, 7.5 or 8.5. Other factors (protein concentrations, unfolding and refolding time, ionic strength and ionic type of the solutions) were also studied. The foaming properties of the treated proteins were evaluated by relative overrun, foam stability, liquid drainage and rheological test. The conformation changes of the proteins were determined by circular dichroism spectroscopy and surface hydrophobicity. Unfolding at pH 2.5 or 3.5 resulted in better overrun than unfolding at pH 1.5 and unfolding at pH 11.5 or 12.5 gave better overrun than unfolding at pH 10.5. Greatest improvements in overrun was found for proteins refolded to pH 8.5 while foam stability was highest when proteins were refolded to pH 4.5. Inclusion of 10 mM CaCl2 did not dramatically change the foaming properties. Increasing the concentration of NaCl did not show improvement of foaming properties except for proteins unfolded at 3.5 and refolded to 8.5. Rheological and molecular studies suggest changes in protein conformation and interactions are responsible for the modified foaming properties. The results showed that the foaming properties of egg white proteins could be tailored by proper modification of their structure using specific pH-induced unfolding and refolding strategies. This suggests that desirable functionality of proteins could be obtained by proper manipulation of their conformation.
Session 17E, Food Chemistry: Proteins
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