| Soybean protein are extensively used for processed food and traditional Chinese foods because of their functional properties and high nutritional value. Soybean proteins consist of two major components, 7S and US globulins, which have different functional properties and structures. In the present study, some investigated functional properties of 7S and US globulins. The literature is scanty concerning a two component interaction between soybean proteins and starch. In this paper, the methods of extraction, isolation of 7S and US globulins were set up, the conformation of 7S and US globulins were detected by FT-IR, AFM, CD, DSC, the gel properties of 7S and US globulins were determined, 7S globulin was modified by chemical and enzymatic methods, a two component interaction between starch and 7S globulin was investigated by texture profile analysis, DSC and rheometer. The results were showed as follow:1. Extraction, isolation, purification and identification of 7S and US globulins in soybeanCrude 7S and US globulins were prepared according to the method of Thanh et al. The crude 7S and 11S globulins were further fractionated with ammonium sulfate. Chromatographic fractionations of the crude 7S and US globulins were performed on a column of Sepharose 6B. The purified 7S and US globulins fractionations were found to be homogeneous from analyse by gel electrophoresis. The protein content of the US globulin and 7S globulin were respectively 95.06% , 95.35%, which were obtained from this chromatography, determined according to the Kjeldahl method.2. The conformation of 7S and US globulinsAs the results of CD spectrum and FT-IR spectrum shown, the secondary structure of 7S and US globulins were mainly a-helix. 7S and US globulins were observed as mainly globular form by AFM, their sizes were about 56nm, 105 nm respectively. The denatured temperatures of 7S and 11S globulins were respectively 58.9℃, 60.6℃, measured byDSC.3. The gel properties of 7S and US globulinsThe emulsification ability of 7S globulin was higher than soybean protein isolate. Heating temperature accelerated proteins gelation during 70-90℃. pH value affected gel texturalproperties intensively. The gels near from pI had a worse textural property. Ionic strength of NaCl weakened hardness of proteins gels. And US globulin couldn't form gel which heated at 95, 45min, 15%(w/v) and I>0.6.4. Chemical and enzymatic modification of 7S globulinThe results indicated that both the modification methods of chemistry and enzyme could take some meliorations to the functional properties of soybean 7S globulin. The capacity of holding water and the emulsification stability of soybean 7S globulin could be greatly advanced by appending acetic acid anhydride (15% v/w ), the absorbency of oil could be evidently advanced by the accession of STP (1% w/w). The capacity of holding water, emulsification and emulsification stability of soybean 7S globulin modified by pawpaw proteinase were evidently advanced while the hydrolyze index was 10.78%. Soybean 7S globulin could be hardly advanced by Asl.398 proteinase.5. A two component interaction between starch and proteinA two component interaction between starch and protein had effects on textural, thermaland rheological properties of protein-starch system. Gel hardness of mixed gel decreasedwhen the protein fraction increased. The textural properties of protein-starch system wereaffected by variety of protein or starch.A pure 7S globulin or potato gel had only one denaturation peak. But multi peaks in7S-potato system were found by DSC scans.The rheological (G',storage modulus) properties had changes with ratio of 7S globulin inmixed systems during heating, heat preserving and cooling.These results showed that the two component interaction between starch and protein wasexisted.
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