title: Role of β-conglycinin and glycinin subunits in the pH-shifting-induced structural and physicochemical changes of soy protein isolate.
abstract: Soy β-conglycinin (7S) and glycinin (11S) were incubated up to 4 h in acidic (pH 1.5 to 3.5) or alkaline (pH 10 to 12) solutions to induce protein structural unfolding followed by refolding 1 h at pH 7.0, a process known as pH-shifting. The pH-shifting markedly increased (P < 0.05) emulsifying activity of 11S and to a lesser extent 7S; the former also produced more uniform oil droplets. The emulsifying activity improvements were accompanied by a significant rise in protein surface hydrophobicity, slight loss of the secondary structure (circular dichroism), and substantial dissociation of disulfide-linked basic and acidic 11S subunits. The findings suggested that 11S globulins of soy protein isolate (SPI) were more responsive to pH-shifting treatments than were 7S globulins, and the resulting emulsifying activity enhancements of 11S, in parallel with that of SPI, were indicative of its determinant role in the overall emulsifying properties of pH-shifting-treated SPI.
  
  
  CONCLUSIONS
  Extreme alkaline (pH 12) and acidic (pH 1.5) medium treatments can significantly modify the structure and enhance the emulsifying properties of both β-conglycinin and glycinin components of SPI. The functionality improvement by the pH processes is more remarkable for the glycinin protein fraction. Therefore, SPI enriched with glycinin seems to be particularly suitable for extreme acidic or alkaline processes to produce surface-active functional ingredients for food applications.
authors.affiliation: State Key Laboratory of Food Science and Technology, and School of Food Science and Technology, Jiangnan Univ, Wuxi, Jiangsu 214122, China.
authors.forename: Jiang
authors.initials: J
authors.lastname: Jiang
authors.forename: Youling L
authors.initials: YL
authors.lastname: Xiong
authors.forename: Jie
authors.initials: J
authors.lastname: Chen
mesh_terms: D052179:Antigens, Plant / Q000737:chemistry* / Q000302:isolation & purification; D055598:Chemical Phenomena; D002942:Circular Dichroism; D004586:Electrophoresis; D045703:Emulsifying Agents / Q000737:chemistry; D004655:Emulsions; D005916:Globulins / Q000737:chemistry* / Q000302:isolation & purification; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D055314:Seed Storage Proteins / Q000737:chemistry* / Q000302:isolation & purification; D012995:Solubility; D030262:Soybean Proteins / Q000737:chemistry* / Q000302:isolation & purification; D013025:Glycine max / Q000737:chemistry; D013438:Sulfhydryl Compounds / Q000378:metabolism
chemical_list: D052179:Antigens, Plant; D045703:Emulsifying Agents; D004655:Emulsions; D005916:Globulins; D055314:Seed Storage Proteins; D030262:Soybean Proteins; D013438:Sulfhydryl Compounds; C013894:beta-conglycinin protein, Glycine max; C011474:glycinin