Surface functional properties of native, acid-treated, and reduced soy glycinin. 2. Emulsifying properties

Emulsifying properties of native and chemically modified soy glycinins were studied. The influence of ionic strength, protein sample composition and c oncentration, and assay conditions on the flocculation-creaming process and coalescence resistance was analyzed. Differences in these emulsifying prop erties were exhibited by native glycinins, which have a variable content of 4S, 11S, and 15S forms. Structure and functionality of native glycinin wer e modified by means of combined treatments: mild acidic treatments without heating or with heating at variable time and with or without disulfide bond s reduction. Modified glycinins presented different degrees of deamidation, surface hydrophobicity, and molecular mass. A slight enhancement of emulsi fying stability at moderated deamidation degrees was observed. In different protein samples, a positive relationship between the flocculation-creaming rate constant and equilibrium oil volume fraction of emulsions with surfac e hydrophobicity was detected. A remarkable difference was observed between reduced and nonreduced samples, mainly with respect to behavior at low or high ionic strength.