Precipitation of Calcium Caseinate by Heat and Subsequent Reversal

The addition of calcium chloride to 2% sodium or calcium caseinate solutions causes a drop in viscosity, perhaps through aggregation since the solutions become opalescent. If the total concentration of calcium is not greater than 0.012 M, heating to 90° C. for 1hour does not change the viscosity, but the solutions become more opalescent and even opaque (white). The opalescence is completely reversible, at the lower calcium concentrations, when the solutions are cooled. At concentrations of calcium above 0.012 M the viscosity is increased by heating to 90° C.; on standing at lower temperatures the viscosity increase is partly reversed in 1 to 3 hours. The viscosity increase is due to the formation of a colloidal precipitate of casein which partly redissolves at lower temperatures. The amount of precipitate is increased by high calcium concentration and low pH values. Other factors that affect the precipitation and re-solution are time of heating, stirring, and temperature after heating. Cream slows up the re-solution of the colloidal casein precipitates.