Relationship between Interfacial Behaviour of Native and Denatured Soybean Isolates and Microstructure and Coalescence of Oil in Water Emulsions - Effect of Salt and Protein Concentration

The capacity of both native (NSI) and denatured (DSI) soybean isolates to stabilise oil in water emulsions under controlled shear stress was evaluated. The effect of protein concentration, thermal treatment of proteins and salt addition were studied. Sodium caseinate (SC) was used as standard protein. Emulsions prepared with NSI and SC were stable against coalescence in the whole range of protein concentration (1-10 mg/mL) in spite of showing different interfacial behaviour. The interfacial pressure of DSI was higher than NSI, according to its high dissociation degree and aromatic surface hydrophobicity. However, the emulsions prepared with this sample were unstable in the whole range of bulk protein concentrations. When NaCl was added, higher coalescence was obtained with NSI and SC emulsions at low protein concentrations, and stabilisation was reached only by increasing protein concentrations. At high protein concentrations(>5 mg/mL), DSI emulsions were stable in presence of salt, due to the formation of rigid flocs resistant to agitation. Droplet size distribution, microstructure and flocculation tendency of droplets explained the differences in coalescence of NSI, DSI and SC emulsions.