| This paper takes low-temperature defatted soy meal as raw material. Homogenization treatment (single or compound homogenization) was used in the preparation of soy protein isolate (SPI) and its fractions (11S- and 7S- rich fraction). The effects of homogenization conditions, the modification of limited hydrolysis followed by high pressure homogenization and the modification of acid treatment followed by high pressure homogenization on the functional properties of the soy protein and its fractions were studied. The mechanism was investigated by analyzing the modified products structure and the state of aggregation or disaggregation in its molecules and subunits, which benefited to confirm the relationship among the modifications, functional properties and structural changes.The effect of high pressure homogenization and microfluidization homogenization on the functional properties of SPI has been compared at the pressure in the range of 40 to 160 MPa. The results revealed that microfluidization homogenization was more effective in the modification of SPI, and the optimum condition of which was at 120MPa and homogenized once. Compared with SPI without modification, the solubility of SPI and 7S both improved and 11S showed a decrease. But the emulsifying properties of these modification proteins showed different tendency. On the other hand, the gel strength of SPI and 7S were enhanced by microfluidization homogenization and both of them showed a shorter gelation time. During processing of microfluidization homogenization, changes of functional properties for midified SPI and 7S rich fraction is similar. These results showed that 7S rich fraction is important to functional properties of SPI.Microfluidization homogenization (120MPa, one pass) could induce the aggregation of SPI and 7S to disassociate, but 11S showed even more aggregation after the treatment. The intrinsic fluorescence measurements showed that microfluidization homogenization treatment of 7S resulted in a red shif indicating a increase in hydrophobic group. Circular dichroism revealed that random coil decreased and theβ- sheet increased. Microfluidization homogenization induced 11S to aggregate, with the total free–SH and surface hydrophobic declined. Limited hydrolysis could improve the protein recovery rate (from 71.62% to 73.64%) during the extraction of 11S- and 7S- rich fraction. The effects of hydrolysis, homogenization and the combination of hydrolysis and homogenization were different on the functional properties of 11S- and 7S- rich fraction. As to the single hydrolysis, it could improve the emulsifying properties of 11S- rich fraction and the solubility of 11S- and 7S- rich fraction, while the increase in particle size of 7S- rich fraction emulsion and the significant decrease in heat-induced gelling properties of 11S- and 7S- rich fraction were also observed. Single homogenization (20 MP, one pass) could not obviously improve the functional properties due to the less intense treatment. The combination of hydrolysis and homogenization could markly promote solubility and emulsifying properties of these fractions, especially to 11S- rich fraction, the particle size distribution and creaming rate were close to NaCN emulsion. Compared with samples treated with hydrolysis, the combination of hydrolysis and homogenization could improve the gel strength and induce the early gelation time.The combination of hydrolysis and homogenization led 11S- rich fraction to aggregate and led 7S- rich fraction to disaggregate. The common characters of these differences were the increasedβ- sheet, improved emulsifying properties, benefited for preparation of small particle size emulsions and decrease in creaming rate.Single acid treatment could result in a slight increase in solubility and water holding capability of SPI. However, there was a significant improvement in the solubility and water holding capability of SPI, after acid treatment combined with homogenization. According to the particle size distribution of the emulsion, which was made with SPI treated with the combining modification and after the process of frozen-thawed, a little difference in the particle size, the sharp monomodal and concentrated distribution, the obvious improvement in freeze-thaw resistance and emulsifying properties were observed. According to the measurements obtained from the HAAKE rheometer, single acid treatment had no obvious effect on enhancing the gel strength. However, acid treatment combined with homogenization could markly induce early gelation time and increase gel strength. This combined treatment could also benefited SPI for improving the textural properties of the whipped cream.After acid treatment, the disaggregation of subunits and recombination of molecules in SPI were induced partial large molecules converted to small molecules, which were verified by electrophoresis and size exclusion chromatograph. The compound effect of acid treatment and homogenization on the subunits disaggregation- molecules recombination could enhance the trend of convertion from large molecules to small molecules and improve some functional properties.
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