11-4 |
Urea-induced polymer formation in the mixed component system of soybean 11S and sesame 13S globulins |
D. ZHU, Lab. of Quality Analysis & Assessment, Div. of Agronomy & Horticultural Science, Kyoto Univ., Graduate School of Agriculture, Gokasho, Uji City, Kyoto, 611-0011, Japan and T. Mori. It has been known that some proteins form gel in the high urea solution by the SH:SS exchange reactions. Both soybean and sesame globulins are important food sources. However, they have been used for foods individually while mixed usages of them have not yet been tried. The aim of the research was to create a new material from the mixed system of the two globulins, thereby developing and providing novel functionalities of the globulins. Soybean 11S and sesame 13S globulins were mixed at pH 7.6 and various ionic strengths in the protein concentration of 11% and 13%, respectively, where 8 M urea was added. After the incubation for about 24 h at the specific conditions, 50 mM NEM was added to terminate the reactions. Our results showed that urea-induced polymers were formed in the mixed component system of soybean 11S globulin and sesame 13S globulins. The SS-SH exchange reaction mainly contributed to the polymerization. Electrostatic interaction was suggested to play also an indispensable role for the polymer formation. The polymers formed in the mixed component systems were characterized by examining the appearance and solubility after the removal of urea and the Ca2+-precipitation behavior, by comparison to the single component systems of the two globulins. The image analysis of transmission electron microscopy showed that the polymers formed at ionic strength 0.01 and 0.5 were aggregates, and the one at ionic strength 1.76 was long, smooth fiber. It was likely from the results that the polymer formed was a so-called polymer blend. Our results suggest that the formation of polymer blend is dependent on the quantity and quality of SH, SS and their exchange reaction and the conformation of the globulins. Improved food functionalities and processing properties can be expected from the new material as compared to their original sources.
Session 11, Food Chemistry: Proteins
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