Precipitation of Casein by the Addition of Sodium Carboxymethylcellulose to Skimmilk

Abstract

The influence of sodium carboxymethylcellulose (CMC) on the casein micelle in milk at the neutral pH was studied. CMC precipitated part of casein in milk. From the relative areas of electrophoretic patterns and sialic acid contents of casein fractions, it was calculated that the CMC-precipitated casein contained 51% αs-, 17% κ-, and 32% β-casein, while the distribution of the whole casein was 44% αs-, 19% κ-, and 34% β-casein.Measurements by ultracentrifugal method indicated that added CMC dissolved a portion of calcium and inorganic phosphorous. But a slight decrease in the dialyzable and ionized calcium was determined by equilibrium dialysis of skimmilk containing CMC. Interaction between CMC and the precipitated casein was not observed. The precipitation of casein did not occur in the skimmilk of which all of the calcium was removed by the addition of potassium oxalate. It appears that CMC combines with the calcium ion and dissociates the colloidal calcium phosphate in skimmilk, and causes the considerable decrease in the stability of the casein micelle to calcium.