The effects of divalent cations in the presence of phosphate, citrate and chloride on the aggregation of soy protein isolate

The protein aggregation-dissociation process induced by divalent cations wa s studied using diluted aqueous dispersions of a native soy isolate. Turbid ity, as a protein aggregation indicator, was quantified at a fixed time aft er addition of increasing amounts of CaCl2, MgCl2 or an equimolar mixture o f them. In all cases turbidity values attained with Ca2+ were higher than t hese obtained with Mg2+. The effects of phosphate, citrate and chloride pre sence were also determined. Phosphate, becomes incorporated into Ca2+-induc ed aggregates, but not in Mg2+ ones. Both citrate and chloride ions inhibit protein aggregation and contribute to the dissociation of previously forme d aggregates. Low citrate concentrations allowed aggregate formation, even at high CaCl2 concentrations; this behavior was not observed in the presenc e of MgCl2. A sedimentation based test was developed as a stability paramet er of dispersions of soy protein aggregates. Results showed that even thoug h aggregation was induced by divalent cations, competition between phosphat e, citrate and soy protein could modify the aggregates' properties. Optimum aggregation conditions were established from combinations of these variabl es. (C) 1999 Canadian Institute of Food Science and Technology. Published b y Elsevier Science Ltd. All rights reserved.