Studies On Microstructures Of Instant Tofu Powders And Solubilizing, Gelling Mechanism Of Its Soybean Proteins

Instant tofu powder is a kind of soybean powder, which can be dissolved rapidly in boiling water and turned into tofu in a few minutes when the coagulation agents are added; the traditional tofu manufacturing process usually takes more than ten hours.Through comparing the ion contents of soybean protein in different states, we conclude that: the denatured soy protein can absorb more high valence cations and form soluble soybean protein aggregation; The soy protein solubility is the lowest when the total concentration of Ca++ and Mg++ is 0.02mol/L; comparing with Mg++, Ca++ makes soybean protein more unstable in soymilk; Ca++ and Mg++ in the final soy product are 20% and 80% of the original quantity in the soybean; Comparing with the soluble soybean protein, the molar ratio of Ca++/Mg++ in insoluble soy protein aggregation is always bigger.By measuring the content of P of phytate and protein in the soybean extraction at different pH, and measuring the relative molecular weight in different heating condition by the gel filtration at the same time, we can conclude that: The phytate and protein form soluble complex in soymilk, the complex can reach the most stable state when the soymilk is heated in adequate methods; When the soymilk is heated strongly, the distribution of the soy protein relative molecular weight becomes wide in the solution; Soy protein in the soymilk is unstable thermodynamically, and the dissolving process of soy protein should be a disperse process.The distributions of the particle diameter in different solution are measured by dynamic laser particle device. The average diameters of SPI are 263.0 and 22.4 nm at 25℃and 55℃, hence, hydrogen bond is the main force of the SPI protein in solution; The particle diameter in no-heated soymilk is about 2000nm, the ration of the 400nm diameter particles is only 2.5% in volume, and the protein aggregation speed is very quick; with the heating strength increasing, the average volume particle diameter decreases continuously, being 2237nm in no-heated soymilk, then being 11.1nm in heated soymilk and finally 4.3 nm after homogenization; The average diameter of oil drop is smaller than 20nm, and the soy protein solubility is no relation with the soybean oil in soymilk.When the concentration of the no-heated soymilk is below 27%, the viscosity coefficient is very low; When the concentration is 42%, the viscosity coefficient is only 8mPas at 60℃, equal to 10% of heated soymilk and only 8 times of the water at room temperature.In the research for the coagulation principle of different coagulation agents, we conclude that: The combination of phytate and soybean protein with high valence cations results in the decreasing of the solution pH; In the measuring pH range, the high valence cations combines...