Effects Of Transglutaminase On Surface Hydrophobicity And Viscosity Of Soy Protein

Natural soy protein has some functional properties, due to inherent structural they are limitaed, and the natural function they demonstrated is not very satisfactory. The transglutaminase was used for modifing proteins and made it with better function properties such as hydrophobicity, viscosity. Four kinds of protein, low temperature defatted soy protein, soy protein isolated, soy 7S globulin (self-preparation) and soy 11S globulin (self-preparation), was modified by transglutaminase with different reaction conditions and determination surface properties, structure.Four kinds of soy protein was modified by Transglutaminase, surface hydrophobicity of protein was measured under different conditions, and single factor and orthogonal experiments was determined. The experimental results show that: After the transglutaminase modified, the surface hydrophobicity of proteins has more improved than the former. As the additives increases, the surface hydrophobicity of low-temperature defatted soy protein, soy protein isolated and soy 7S globulin with transglutaminase-modified increase and than decrease ,in the amount of enzyme 40U / g , the surface hydrophobicity was the largest. And for soy 11S globulin ,the amount of enzyme 30U / g. By transglutaminase modified protein, the largest surface hydrophobicity is soy 7S globulin, followed by soy protein isolated, soy 11S globulin, and low-temperature defatted soy protein have least surface hydrophobicity.Viscosity of four kinds of protein with transglutaminase modification was determination. Results as follows: viscosity of modified protein has improved on varying degrees. Because of transglutaminase additives,makes the system of mutual protein polymerization, with the polymer molecular weight increases, the apparent diameter become larger, thus leading to viscosity increased. Viscosity of defatted soy protein, soy protein isolated and soybean 11S globulin by transglutaminase modified increased with the same trend basically at different pH. From the pH 5.0 ~ 8.0, the protein viscosity showed slow growth trend, when the pH is higher than 8.0 the protein viscosity growth rapidly. Viscosity of four types of modified protein was basically the same changes with reaction temperature and reaction time on the protein viscosity was less affected.Through enzyme-modified the molecular weight of protein changed. The result can find in SDS-PAGE. Part subunit bands of 7S globulin disappeared, acidic subunit of modified 11S globulin steady decline, alkaline subunit no significant changes. one of the soybean 7S globulin subunits and three subunits of soybean 11S acidic disappeared in modified defatted soy protein and soy protein isolated. Soy protein crosslinking polymerization was happened with transglutaminase modified , so that the polymer molecular weight increased, it can not enter the separation gel and localize at the same place.DSC including denaturation temperature and denaturation enthalpy were determined for the largest surface hydrophobicity of modified protein and unmodified protein. The endothermic temperature range of modified protein was significantly higher than unmodified protein. larger molecular weight polymer was formed by Polymerization catalyzed by transglutaminase , it was more tolerant of high temperature, that is the thermal stability of soy protein modified by transglutaminase was enhanced.Soy protein particles have increase of different levels by transglutaminase cross linking ,that protein has been assembled. Surface structure of low-temperature defatted soy protein modified was irregular floc structure. Spherical particles of soy protein isolated have smooth surface and protein isolated was modified by transglutaminase that have empty and connect into network structure. 7S protein and 11S protein particles by cross-linking have the formation of irregular floc structure.