Amino acid grafting of beta-lactoglobulin mediated by phosphorus oxychloride

beta-Lactoglobulin was phosphorylated with 80 mol of POCl3/mol protein in the presence of triethylamine and amino acids or their esters added at a total molar excess of 6 mol base/mol POCl3. The extent of phosphorylation was reduced when the amino acids replaced triethylamine as the base. Arginine and lysine were grafted to protein molecules in amounts proportional to the beta-lactoglobulin phosphorylation, while histidine grafting was very weak. The electrophoretic patterns of the modified proteins showed increased negative charges, reduced isoionic points and slight dimerization. The emulsifying properties of the modified proteins were improved.