Effect Of Processing Technology On The Proterties Of Soymilk Protein And Evaluation Of Products

As an important kind of soybean product, soybean milk is rich in various nutritional and functional material needed for human growth and development, and is increasingly becoming an essential health drink of modem life. Nevertheless, the soymilk products are easy to appear precipitation, stratification and other phenomenon in shelf period. And there are instability and storage problemsin the products due to the changes of soybean protein structural feature during processing. In recent years, domestic and overseas scholars have carried on deep research to this question, but not solved this problem from the perspective of improving protein structural proterties. Therefore, this research is carried out on the effect of soymilk processing technology on the structural proterties of proteins, and on the appropriate process and technology parameters in soymilk protein degeneration processing. And the aim of this research is to denature the protein properly and develop high protein and high stability soymilk products, providing theoretical support for soymilk industrialized production. The main research contents and results are as follows:(1) Effect of pulping conditions on extraction rate of soybean protein.Study the effect of the pulping conditions including pulping water quality, the water temperature and the material-to-liquid ratio on raw soybean protein extraction rate. Results showed that the optimum condition was water temperature of grinding beans was 80℃, material-to-liquid ratio was 1:7, and the distilled water was used as pulping water. Under this conditions, soybean protein extraction rate was up to 74.10%.(2) Effect of heat treatment on protein denaturation of soybean.NSI value and activity of urease were taken as monitoring indexes, and the effect of different thermal treatments(atmospheric heating process, microwave heating process, high pressure heating process and high hydrostatic pressure processing) and technology parameters on the protein denaturation condition was studied. The results showed that proper heat treatment methods and technology parameters can increase NSI value and decrease activity of urease. The optimal atmospheric heating processwas heating at 90℃ for 15 min, improving NSI value to 81.62% and reducing urease activity to weakly positive. The optimal microwave heating process was heating at 650 W for 40 s, improving NSI value to 75.35% and reducing urease activity to weakly positive. The optimal high pressure heating process was heating at 100℃ for 3 min, improving NSI value to 91.31% and reducing urease activity to weakly positive. And the optimal high hydrostatic pressure processing was heating at 80 MPa for 20 min, and NSI value was73.43% and urease activity was strongly positive. Above all, atmospheric heating process, microwave heating process and high pressure heating process, which make the protein denatured properly and decrease the activity of urease, were the suited pre-heating methods.(3)Effect of homogenization on solubility of soybean protein.Study the effect of temperature, pressure and times of homogenization on the solubility of soybean protein in the pre-heating soymilk semi-products. Results showed that the homogenization conditions had significant effect on soy protein NSI value, and different pre-heating soymilk semi-product had different optimal homogenization conditions. The protein NSI value of atmospheric pre-heating soymilk semi-product reached optimum value of 88.69 % after homogenizing once at 65 ℃ and 80 MPa.The protein NSI value of microwave pre-heating soymilk semi-product reached optimum value of 87.47% after homogenizing twice at 25 ℃ and 40 MPa. And the protein NSI value of high pressure pre-heating soymilk semi-product reached optimum value of 94.12% after homogenizing once at 25 ℃ and 80 MPa.(4)Effects of different processing technologies on the structural proterties of soymilk protein.Protein NSI value, free sulfhydryl content, surface hydrophobicity, particle size distribution and transmission electron microscope(TEM) images were taken as indexes to analyze the effect of atmospheric technology, microwave technology and high pressure technology on the protein in soymilk. It was suggested that pre-heating and homogeneity increased the NSI value, while sterilization process decreased the NSI value. The free sulfhydryl contentwas decreased in the pre-heating process and then rose. Pre-heating and homogeneity technologies increased the surface hydrophobicity due to the expansion of protein, and decreased after the sterilization process. According to the results of particle size distribution and TEM images, pre-heating process denatures the proteins, leading to the stretch of peptide chain, molecules dissociation or aggregation(mainly aggregation), changing from spherical to irregular shape of molecular and the decrease of particle size. Homogenization process made the protein smaller and equally distributed. Sterilization process could make protein in the soymilk to aggregate and make the molecular size increase. The indexes of intramolecular bonds, particle size and TEM images verified with each other.(5)Analysis of the soymilk featurefrom different processing technologies.Physical and chemical indexes, health indicators, stability and sensory characteristics of the three soymilk products from the atmospheric process, microwave process and high pressure process reached the national standard requirements.