Heat-induced Self-assembly Fiberils Of Different Components Of Soybean Proteins And Their Interaction

In recent years, soybean proteins have been widely used in food industry for their high nutritional value. In unconventional conditions, proteins can form different aggragates through controlling concentrate,pH, temperature and components. Especilly, self-assembly fibrils can be formed at low pH and low ionic strength for long time heating. The aim of this thesis is to study the morphology diversity of different aggragations, which is formed from four soybean proreins with different processings and four components(7S,11S,acidic,Basic) respectively. Also we studyed the effect of7S,11S,basic subunits on the formation of acidic subunits fibrils. In addition, we studied the differences among aggragates by analyzing the applied force(disulfide bond, free sulphydryl, surface hydrophobicity), the kinetic parameters (ThT), properties (turbidity, DSC, SDS-PAGE, CD) and interface properties (foaming and emulsifying properties). The main results were as follows:Firstly, different morphology aggregation can be formed from four kinds of soyben proteins(SPIA,SPIG,TZ,ZZ) when heated at pH2.0and90℃for10h. SPIA aggregated into fibrillar amyloid-like aggregate. The results of Thioflavin T(ThT) showed that (df/dt) max and fluorescence intensity of SPIA were largest and its fmax SPIG137.07%and TZ49.53%respectively. The surface hydrophobicity were determined. The free sulfhydryl groups of SPIA reduced29.73%lower than the other three kinds of materials.Secondly,7S,11S, acidic and basic subunits have different amino acids compositions, structures. Different morphology aggregates can be formed from four kinds of soyben proteins conponents (7S,11S, acidic subunits,basic subunits) when heated at pH2.0and95℃for20h. The results showed that7S and acidic subunits can form fibril aggregates, while11S and basic subunits formed non-twig-like polymer.We further compared the formation of different polymers from four components (7S,11S,acid subunits,basic subunits) on turbidity, Thioflavin T(Th T) and major force. Thioflavin (ThT) results showed that the fluorescence intensity of acid subunits and7S were larger than11S and basic subunits. However, ThT fluorescence intensity of the basic subunit were too small withnot meetting the ThT fluorescence kinetics linearity. The (df/dt) max of7S and acidic subunits was higher than11S’by approximately21and12.7times, respectively. And the fmax of7S was higher than11S and acidic subunits respectively3.5and1.2times. The turbidity of7S reached a maximum heating for8h then slowly decreased, while11S increased with heated. The results of free sulfhydryl groups of7S,11S, acid subunits, basic subunits decrease18.96%,54.19%,27.89% and33.83%,indicating that the disulphide bonds played a supporting role in forming fibrils aggregates. The surface hydrophobicity showed that the formation of fibrils had a slow polymerization rate, while the formation of other polymers had a fast polymerization rate.Compared with the conventional protein aggregation, the results indicated that fibrils aggregates had higher foam ability and foaming stability, there is obviously promotion in foaming stability with silent period prolonged. Compared with the conventional protein aggregation, the foam stability of fibrils formed from7S and acidic subunits was higher by approximately21and5.5times when the foam films silent30min. However, fibrils have little effect on emulsification property. Fibrils can be formed from acidic subunits when heated at pH2.0and95℃for20h and we further study the effect of pH, temperature,NaCl,CaCl2,heating time on the formation of acidic subunits fibrils. Shorter fibrils with more particle aggregates were formed from acidic subunits in the presence of50mM NaCl. And shorter fibrils with more branched were formed from acidic subunits in the presence of50mM CaCl2.Finally, we compared the effect of7S,11S, basic subunits on the formation of acidic subunits fibrils. The results showed that fibrils were formed when7S were added, while clusters aggregates were formed when11S and basic subunits were added. Thioflavin T fluorescence intensity becomed stronger when7S were added. Turbidity results indicated that fibrils have lower turbidity, and slowly increased. In the formation of acidic subunits fibrils,7S reduced the formation of4.99%disulfide bonds, while11S and basic subunits, respectively, increased39.7%and13.48%disulfide bonds. The results of surface hydrophobicity showed that the formation of fibrils had a higher polymerization rate.Circular dichroism (CD) showed the amount of a-helix required a significant reduction in the formation of fibrils. Acidic subunits and7S reduced from11.1552%±0.23and7.2659%±0.23to4.4841%±0.26and5.9288%±0.16. While the amount of a-helix of basic subunits reduced from6.3049±0.34to6.0428±0.29.7S and basic subunits have the amount of a-helix6.3049±0.34and7.2659±0.23, respectively. Both7S and acidic subunits were added to acidic subunits, and the amount of a-helix reduced from17.1168%±0.24and18.4211±0.14to5.9616%±0.19and9.3636%±0.18. Indicating that7S was benefit to the formation of acidic subunits fibrils.