The Preparation Of Soy Protein With High Emulsifying Property

Emulsifying property is one of the important functional properties of soy protein, but its relatively poor emulsifying capacity and emulsion stability limit its application in food systems. The objective of this paper was to use acid/alkali modification, heat treatment, enzyme modification and food emulsifiers in the preparation of soy protein, and fully study the properties of the final products. This study would be helpful for optimization of soy protein processing, and provide new ideas about the preparation of soy protein with high emulsifying property to broaden the application of the products.Firstly, the effects of acid/alkali modification on the improvement of emulsifying property of soy protein concentrate and soy protein isolate were studied. The results showed that the modified products had improved emulsifying capacity and emulsion stability, especially for the products treated by alkali (pH11, 6h). The results of SDS-PAGE, HPLC and dynamic light scattering showed that the acid modification induced the aggregation and dissociation of 11S subunit, the particle size distribution of the products was broaden; the alkali modification led to the cross linking among protein molecules and many soluble aggregates were generated. The surface tension of the proteins modified by alkali (pH11, 6h) decreased and the surface hydrophobicity increased.Secondly, the effects of heat treatment on the improvement of emulsifying property of SPI were studied. Results showed that the emulsifying capacity and emulsion stability and surface hydrophobicity of protein improved evidently while surface tension decreased after treated under 80℃for 5min. With a longer heating time and a higher heating temperature, the emulsifying capacity and solubility of modified protein decreased gradually. The results of dynamic light scattering showed that some large particles generated. The results of HPLC showed that protein molecules aggregation and dissociation occurred during the heat treatment, the molecular weight distribution was broaden, the content of aggregates significantly increased.The effects of enzyme modification to the emulsifying property of SPI were also investigated. After hydrolyzed by papain, the emulsifying property of SPI hydrolysates decreased. On the contrary, after the hydrolysis of pancreatin for 30min, the emulsifying capacity of hydrolysates significantly increased while surface tension decreased and surface hydrophobicity increased. The results of molecular weight distribution analysis and electrophoresis showed that hydrolysis by papain led to the dissociation of protein subunit and the molecule weight of hydrolysates were smaller than 30kDa mostly. After hydrolyzed by pancreatin, 11S subunit dissociated and the small fractions cross linked by disulfide bond, the molecular weight distribution was broaden.Based on the modification technology, the effect of emulsifiers on the emulsifying property of soy proteins was studied. The technology conditions for the preparation of soy proteins with high emulsifying property was determined: using heat-treatment (80℃, 5min) modified SPI as the main material and combining with sucrose ester (3g emulsifier/100g protein) could make the soy protein products with high emulsifying property (EAI:36.8m2/g, ESI:678.4min). In the respect of the relationship between the structure and the emulsifying property, it was found that the solubility and the contents of soluble aggregations had an important effect on the emulsifying property; the surface tension and the surface hydrophobicity had an important effect on the emulsion stability; the content of micromolecule protein had no significant correlation with the emulsifying property.