Precipitation of Milk Proteins by Sodium Carboxymethylcellulose

A study was made to determine optimmn conditions for precipitation of milk proteins by sodium carboxymethylcellulose and to elucidate the chemical nature of the resulting gum-protein complex. Carboxymethylcellulose precipitated a maximum of 90 to 96% of the casein from a simplified casein system and about 71% of the total protein (principally casein) from natural skimmilk. Maximum protein precipitation occurred at pit 7.5 in simplified casein systems and results indicate a similar relationship in natural skimmilk. The reaction was calcium-dependent, and protein-calcium-carboxymethylcellulose bridging appears to be involved at pH levels above the isoelectric point of casein. At the isoelectrie point (pH 4.6), carboxymethylcellulose stabilizes casein, preventing precipitation. The typical cellulose-protein complex contained 51.7% protein, 7.3% ash, 0.44% calcium, and 10 to 17% carboxymethylcellulose.