The formation of soluble aggregates from insoluble precipitates of commercial soy protein isolate (SPI) by means of combined homogenization and ultrasonic treatment was characterized. The heat-induced gelation of formed soluble aggregates was also investigated. The turbidity and electrophoresis analyses showed that initially insoluble precipitates of commercial SPI, most basic subunits of glycinin included, were transformed into soluble aggregates. High performance size exclusion chromatography (HPSEC) analysis confirmed the formation of soluble aggregates. Both non-covalent and covalent interactions, e.g. hydrophobic interactions, hydrogen bonds and disulfide bonds, were involved in the formation of soluble aggregates. The formation of soluble aggregates remarkably improved the heat-induced gelling ability of commercial SPI. (c) 2008 Elsevier Ltd. All rights reserved.