Interfacial Rheology and Foaming Properties of Soy Protein and Hydrolysates under Acid Condition

In this study, the foamability of soy protein isolate (SPI), β-conglycinin (7S), soy protein selective hydrolysates (SPSH) and soy protein limited hydrolysate (SPLH) were tested at both acid and neutral conditions (pH 2.0, 3.0, 4.0 and 7.0). The properties of soy proteins (SPI and 7S) and hydrolysates (SPSH and SPLH) were analysed by particle size distribution, zeta potential, surface tension, interfacial rheology, foam expansion and stability. The particle size of soy proteins and hydrolysates decreased near the isoelectric point (pH 4.0). The 7S, SPSH and SPLH under acid conditions had lower surface tension than at pH 7.0. Under acid conditions, the higher foaming expansion of 7S, SPSH and SPLH than those under the neutral condition could be explained by lower surface tension, quicker adsorption and stronger viscoelastic properties; the better foaming stability can be attributed to a robust interfacial film. In summary, the SPSH and SPLH can be effective alternatives to egg white in aerated food due to the high foamability at both acid and neutral conditions.