Functional Properties of Chemically Phosphorylated Whole Casein

Abstract The functional properties of unmodified whole casein were compared with those of casein that had been chemically superphosphorylated using phosphorus oxychloride at three different pH values. Casein modified at pH 5, 7, and 9 had an additional 3.30, 4.78, and 6.75 mol of P bound/mol of casein, respectively, either as monophosphates when modified at pH 5 and 7 or as mono-, di-, and polyphosphates when modified at pH 9. Solubility studies indicated that the isoelectric point of the modified caseins shifted to the acid side of pH 4.6 as the amount of bound P increased. None of the modified caseins was as soluble in water at pH 7 as the unmodified control, and caseins modified at pH 5 and 7 had lower solubility than casein modified at pH 9. Compared with control casein, casein modified at pH 9 was more soluble in the presence of Ca 2+ , and caseins modified at pH 5 and 7 were less soluble. Superphosphorylated caseins had improved foam stability and poorer emulsion stability than the controls. Superphosphorylation of whole casein altered the ability of the casein to interact with its environment, as demonstrated by the changes in its functional properties, which could be of value in creating or improving food products.