pH Shifting alters solubility characteristics and thermal stability of soy protein isolate and its globulin fractions in different pH, salt concentration, and temperature conditions

J Agric Food Chem. 2010 Jul 14;58(13):8035-42. doi: 10.1021/jf101045b.

Abstract

Soy protein isolate (SPI), beta-conglycinin (7S), and glycinin (11S) were subjected to pH-shifting treatments, that is, unfolding at pH 1.5 or 12.0 followed by refolding at pH 7.0, to induce molten globule structures. Treated samples were analyzed for protein solubility, thermal stability, and aggregation in 0, 0.1, and 0.6 M NaCl solutions at pH 2.0-8.0. The pH(12) shifting resulted in drastic increases (up to 2.5-fold) in SPI solubility in the pH 6.0-7.0 range, especially at 0 M NaCl. The pH(1.5) shifting had a generally lesser effect on solubility. 11S exhibited a solubility pattern similar to that of SPI, but the solubility of 7S was unaffected by pH shifting except at 0.6 M NaCl. The pH shifting, notably at pH 12.0, produced soluble, disulfide-linked polymers from 11S and reduced (P < 0.05) its enthalpy but not its temperature of denaturation. Soy proteins structurally altered by pH shifting had a reduced sensitivity to thermal aggregation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antigens, Plant / chemistry*
  • Antigens, Plant / isolation & purification*
  • Globulins / chemistry*
  • Globulins / isolation & purification*
  • Hot Temperature
  • Hydrogen-Ion Concentration
  • Protein Stability
  • Seed Storage Proteins / chemistry*
  • Seed Storage Proteins / isolation & purification*
  • Sodium Chloride / chemistry
  • Solubility
  • Soybean Proteins / chemistry*
  • Soybean Proteins / isolation & purification*

Substances

  • Antigens, Plant
  • Globulins
  • Seed Storage Proteins
  • Soybean Proteins
  • beta-conglycinin protein, Glycine max
  • Sodium Chloride
  • glycinin