11-5 |
Microstructure and rheology of hetero-aggregates made of soybean 11S and sesame 13S globulins in high urea solution |
D. ZHU, Food Function Div., National Food Research Institute, Food Physics Lab., 2-1-12 Kannondai, Tsukuba, Ibaraki, 305-8642, Japan and T. MORI, Graduate School of Agriculture, Kyoto Univ., Gokesyo, Uji, Kyoto, 611-0011, Japan. Mixed protein solution systems can be applied in much wider fields such as foaming and emulsion, other than gelation. The investigations of formation mechanism and the structures of mixed protein solutions are considered to be important to the functionalities. The objective of this study was to relate the rheological behavior of hetero-aggregates formed in the mixed system of soybean 11S and sesame 13S globulins in high urea solution to their microstructure, using transmission electron microscopy (TEM) and dynamic rheological measurement. We obtained two types of hetero-aggregates from the mixture of soybean 11S and sesame 13S globulins. One is random aggregate formed at ionic strength 0.01; another is strand-like aggregate formed at ionic strength 1.76. It was found that 2-4 weeks aging was necessary to gain stable structure. By aging, the shape of random aggregate did not change but its size decreased; whereas strand-like aggregate underwent a structural rearrangement from random aggregate to very long, regular fiber. Meanwhile, dynamic rheology determination showed that G¢ (elastic modulus) remained unchanged for the random aggregate but increased significantly for the strand-like aggregate. Frequency sweep spectra indicated that the random aggregate had a spectrum at which G² (viscous modulus) kept higher than G¢ at low frequency and overlapped at high frequency (> 6); while strand-like aggregate had a spectra at which G² developed faster than G¢ and crossed at low frequency 0.4. It was suggested that the rearrangement was probably attributed to the electrostatic interaction and that SH:SS exchange reaction rate played a primary role for the formation of strand-like aggregate.
Session 11, Food Chemistry: Proteins I
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