Emulsifying Properties of Acidic Subunits of Soy 11S Globulin

The emulsifying properties of the acidic subunits (AS11S) isolated from soy glycinin (11S) have been studied. The isolated AS11S existed in solution mainly as a dimer species. Circular dichroic analysis indicated only a slight increase in aperiodic structure and no significant difference in β-sheet structure when compared with those of soy 11S. At similar experimental conditions, the emulsifying properties of AS11S were superior to those of soy 11S and heat-denatured 11S. Emulsions prepared with 1% AS11S remained very stable without any visible oil separation for more than a month under gentle agitating conditions, whereas those prepared with 1% 11S collapsed and separated into phases within 2−3 days. The AS11S-stabilized emulsions were very stable below 0.15 M ionic strength. Studies on the rate of adsorption and surface tension reduction at the air−water interface showed that AS11S was significantly more surface active than soy 11S. It is proposed that, because the mass fraction of acidic subunits in soy 11S is ∼60% and it is relatively easy to separate the acidic subunits from soy 11S, it may be industrially feasible to develop an economical process to isolate functional acidic subunits for use in emulsion-based food products. Keywords: Soy proteins; glycinin; acidic subunits of soy 11S; emulsifying properties; emulsion stability