STRUCTURAL-PROPERTIES OF HEAT-INDUCED SOY PROTEIN GELS AS AFFECTED BYIONIC-STRENGTH AND PH

Hydration properties of acidic soy protein gels, prepared with differe nt salt solutions, were studied. The type of bonds that stabilize gel structure and the nature of protein species that make up and stabilize such structure were also investigated. The microstructure of gels was evaluated by scanning electron microscopy (SEM) and water-holding cap acity (WHC) assays. The stability and nature of protein fractions of g el matrices were analyzed by solubility measurements and sodium dodecy l sulfate-polyacrylamide gel electrophoresis. The WHC of gels prepared with NaCl and CaCl2 decreased with increasing salt concentration. Thi s fact suggested, as was corroborated by gel SEM, that at high ionic s trength a more open matrix was formed. The structure of acidic gels, s tabilized by noncovalent bonds, changed with NaCl addition. Both 7S an d 11S globulin subunits participated via hydrophobic interactions to t he stability of pH 2.75 gels. At pH 3.50 the gel matrix was stabilized by hydrophobic interactions among beta-conglycinin subunits, whereas the AB-11S subunit and the AB-11S polymers, linked by disulfide bonds, would be soluble in the matrix interior due to the glycinin fraction that remains native after thermal treatment.