Study On Fractionation Of Soybean Proteins

7S (β-conglycinin) and 11S (glycinin) are two major components of soybean storage protein. Their functional and nutritional properties are different from each other.It's an imprptant way to improve flavor of soybean seeds with soybean protein fractionation. In this thesis, a new soybean fractionation was established with thermal treatment to defatted soybean flours, adjustmengt of pH and addition of NaCl, giving lower lipid contents in soybean fractions. The following conclusions were drawn from this essay:(1) Effects of temperature, pH and NaCl on protein contents and yields, purities and lpipd contents of soy protein fractions were studied in this essay. Three kinds of thermal treatments and different contents of NaCl were discussed in details. The optimized fractionating procedure was as follows: defatted soybean flour was firstly processed with 70℃dry-heating for 2h and dispersed in water at 15:1 (v/w) water-to-flour ratio and extracted at pH 8.0 for 2 h. Centrifugation was performed after the extraction to remove the insoluble residue. The pH of the supernatant was adjusted to 5.8 before adding 10 mM sodium bisulfate. After another centrifugation, an 11S-rich fraction was recovered as the precipitated curd. The second supernatant were adjusted to pH 5.0 and incubated at 55℃for 15 min. Centrifugation was performed after the second supernatant were added with 50 mM NaCl and adjusted to pH 5.5, then LP fraction was recovered as the precipitated curd. The 7S-rich fraction was separated by adjusting pH of the third supernatant to 4.5. The result showed that defatted soybean flour that pre-processed with 70℃dry-heating for 2h improved the separation of 11S-rich fractions from LP and 7S-rich fractions,addition of NaCl by 50 mM helped to fractionate LP from 7S-rich fraction.(2) Difference between optimized fractionations and traditional fractionations were be detected in protein yields, protein and lipid distribution, SDS-PAGE, thermal behaviors and solubility and emulsification activity. Protein yields of both 11S-rich and 7S-rich fractions from the optimized fractionation were higher than those from Nagano procedure with the total protein yields higher too. More soybean proteins were distributed in 11S-rich and IM和LP fractions than in 7S-rich fractions for the optimized and Nagano procedures. Soy proteins were mostly distributed in the fraction of LP for the optimized fractionation and 11S for Nagano procedure. Lower lipids were distributed in 11S-rich and 7S-rich fractions than in IM or LP fractions with LP richest in lipids than any other fraction. The purity of 7S-rich fraction from the optimized fractionation was 8 % higher than that of Nagano procedure. The 11S subunits represent in LP and IM fractions were more than 7S subunits. The percentage of storage protein in LP was less than that in IM. The contaminating 7S-rich in 11S-rich fraction were mostly denatured for both fractionations. More denaturalization took placed in LP fraction of the optimized than in IM fraction of Nagano. The isoelectronic point of protein fractions discussed above were pH 4.5. The solubility of LP produced from the optimized procedure was insensitive to pH in wide range. The emulsification activities were relatively high for 7S-rich fractions with LP fraction inferior to any other fraction.(3) The aggregation kinetics behaviors of 11S-rich, LP and 7S-rich fractions were engaged in this thesis thanks to FBRM. There was obvious difference in the aggregation moment, chord length a non-thermal treatment defatted soybean flours when 11S-rich fraction was precipitated. The addition of NaCl made the counts of aggregations increased. The counts of chord length of <10μm and <10-50μm increased when adjusting pH to 4.5 and trended to be stable later. The mean aggregation chord length of 7S-rich fractions incubated at 55℃was 10μm larger than that of non-incubation counts of aggregation when 11S-rich fraction was precipitated between thermal treatments.