Effect of concentration and incubation temperature on the acid induced aggregation of soymilk

The molecular details of the aggregation of soy protein particles in soymilk during acid-induced gelation using glucono-delta-lactone (GDL) were investigated. Soymilk samples were prepared from different water-to-bean ratios and contained approximately 4% and 7% protein. The effects of protein concentration and incubation temperature (30 or 7 degrees C) on soymilk gelation were observed using rheology and diffusing wave spectroscopy at two different GDL concentrations. During acidification, there was a decrease in electrostatic repulsion between particles which well correlated with the pH of aggregation determined by dynamic light scattering. Gelation of soymilk occurred at about pH 5.8, and neither the rate of acidification nor the protein concentration affected the gelation pH. Gel stiffness was affected by protein concentration. A detailed study of the soluble fraction during the preceding stages of aggregation clearly demonstrated that glycinin components were the first to destabilize during acidification, followed by the beta-conglycinin subunits. Decreasing the incubation temperature from 30 degrees C to 7 degrees C increased the pH of gelation and the gel modulus (G') measured by rheology. It was concluded that short range interactions play a major role in the formation of the protein network in soymilk curd. (C) 2012 Elsevier Ltd. All rights reserved.