Study On Limited Enzymatic Hydrolysis Of Soy Protein Concentrate And Soy Protein Isolate And Modification In Functional Properties

Soy protein was not only better in nutrition and health protection, but also in functional properties. It was highly and widespread applied in food and other fields because of its functional properties such as solubility, water-holding capacity, oil absorption, emulsification, gelation in the process of food production. At present, the researches of modification in functional properties of soy protein were popular in food science. In this study, soy protein concentrate (SPC) and soy protein isolate (SPI) were limited enzymatic hydrolyzed (Trypsin or Neutrase) through enzymatic modification technics, to prepare modified soy protein products with low DH by controlling the hydrolysis extent of soy protein. Changes of functional properties should be evaluated and a new approach of modification of soy protein was trying to find, in order to achieve the goal of improving and holding some important functional properties. In addition, SDS-PAGE was used to determine the modes of enzymatic hydrolysis for soy protein and modified soy protein. And finally it's found that a relationship existed between mode of enzymatic hydrolysis and corresponding modification in functional properties. It could be the key to open out the changes of functional properties. The results obtained in this study are as follow:1. The optimal extracting conditions of defatted soy flour were determined by orthogonal design. With protein content of Soy Protein Concentrate (SPC) as main index, the soy flour was extracted at ethanol concentration 65%, 50℃for 60 min, raw material to solvent ratio was 1:10. And the second extraction was at ethanol concentration 70%-80%, 70℃-75℃for 5 min. The results showed that the protein content increased till the maximum with the time of ultrasonic treatment increasing. If the time of ultrasonic treatment continued increase, the protein content declined instead. The optimal ultrasonic treatment qualification was 15min. The power of ultrasonic treatment also has effect on protein content. With the power of ultrasonic treatment increasing, the protein content also increased. The experiment confirmed that ultrasonic treatment had positive effect on soy protein.2. Neutrase and Trypsin were chosen as hydrolase to limited hydrolysis SPC. The corresponding hydrolysis parameter of Neutrase was that natural pH, temperature 25℃, substrate concentration 10% and enzyme addition 400 U·g-1. The corresponding hydrolysis parameter of Trypsin was that natural pH, temperature 35℃, substrate concentration 10% and enzyme addition 1700 U·g-1. In the same way, Neutrase and Trypsin were chosen as hydrolase to limited hydrolysis SPI. The corresponding hydrolysis parameter of Neutrase was that natural pH, temperature 25℃, substrate concentration 7.5% and enzyme addition 250 U·g-1. And the corresponding hydrolysis parameter of Trypsin was that natural pH, temperature 35℃, substrate concentration 7.5% and enzyme addition 610 U·g-1.3. The analyses of SDS-PAGE indicated that different enzyme had different enzyme specificity. Under the condition of low hydrolysis degree, the modes of enzymatic hydrolysis for soy protein were different. The peptides of modified SPC or modified SPI were short after hydrolyzing by Neutrase. And two new peptides appeared at the bound of low molecular weight. On the contrary, the peptides of modified SPC or modified SPI were long comparatively after hydrolyzing by Trypsin, but there was no new peptide. The differences of the modes of enzymatic hydrolysis would have different effects on functional properties of modified soy protein.4. The solubility of modified SPC was increased distinctly (NSI improved 25 times). The water-holding capacity and oil absorption also were improved, about 14% and 29% growth respectively. Emulsifying activity index and emulsion stability index grew remarkably, but gelation was reduced greatly. All these changes were related to the modes of enzymatic hydrolysis for soy protein. The modified SPC, its solubility, oil absorption and emulsion were equal to commercial SPI, or even better. It indicated that limited enzymatic hydrolysis assuredly can improve and hold some functional properties of soy protein purposefully. As same as SPC, there was also an inherent relationship between mode of enzymatic hydrolysis for SPI and corresponding modification in functional properties. Modified SPI with Trypsin had more long peptides, so its water-holding capacity, gelation and emulsion were better than SPI modified by Neutrase, especially is the hydrolysate which DH% was 1, but its solubility was a little lower instead. Several important functional properties of modified SPI, such as solubility (NSI improved 29 times), emulsifying activity index, emulsion stability index of modified SPI with Trypsin and water absorption, were better than commercial SPI.Consequently, the method of limited enzymatic hydrolysis of soy protein could achieve the goal of improving and holding some important functional properties. Even with the analyses of SDS-PAGE, it's found that a relationship existed between modes of enzymatic hydrolysis and corresponding modification in functional properties. This can offer evidence for studying the changes of functional properties and controlling functional properties.