Characteristics of soy protein isolate/gum arabic-stabilized oil-in-water emulsions: influence of different preparation routes and pH

The properties of oil-in-water emulsions containing soy protein isolate (SPI) with or without gum arabic (GA) have been studied under different pH and different preparation routes. Three routes were used for the preparation of emulsions (10% (w/v) oil and 0.5% (w/v) SPI with or without 0.5% (w/v) GA). In emulsions I, SPI solution with/without GA were first pH adjusted followed by homogenization with oil; in emulsions II, the oil was directly emulsified with SPI-GA coacervates at pH 4.0 to form the 'mixed emulsions', then pH was adjusted; in emulsions III, GA was added to a SPI-stabilized emulsion followed by pH adjustment. The results showed that pH adjustment before or after homogenization with oil greatly influenced the droplet size and emulsifying stability whether for the SPI emulsions or SPI/GA emulsions. The emulsions III showed much slower flocculation rate and higher emulsifying stability at pH 4.0-7.0. The microstructures of SPI-GA emulsion III were more uniform, with the comparably smallest d 43 values in the presence of SDS. It could be indicated that the preparation routes of emulsions greatly influenced the stability of SPI-control emulsion or SPI-GA emulsion. pH adjustment before or after homogenization with oil greatly influenced the droplet size and emulsifying stability of emulsions.