Effect of added monovalent or divalent cations on the rheology of sodium caseinate solutions

Addition of either monovalent (K+, Na+, NH4+) ordivalent (Ca2+, Mg2+, Zn2+) cations had a dramatic effect on the apparent viscosity of sodium caseinate solutions. For monovalent salts apparent viscosity increased exponentially with added ionic strength. For example, with sodium chloride addition to 14% w/w sodium caseinate the apparent viscosity at 25degreesC and 91.2 s(-1) increased from 2 Pa s with no added salt to about 250 Pa s at 1.5 added ionic strength. It is suggested that, this effect is caused by the salt competing successfully with the caseinate for water and so effectively increasing the protein concentration. For divalent salts apparent viscosity increased with added ionic strength to a maximum and then decreased again. The decrease was caused by protein aggregation or micellization, which was accompanied by visible milkiness on addition of calcium chloride. (C) 2002 Elsevier Science Ltd. All rights reserved.