RHEOLOGY AND MICROSTRUCTURE OF CHEMICALLY SUPERPHOSPHORYLATED WHOLE CASEIN

Whole bovine casein was chemically modified using POCl3 to contain 9.1 , 10.6, and 12.5 mmol of bound P/mmol of casein [(160, 190, and 220% P , respectively) relative to the 5.6 mmol of P/mmol of unmodified casei n (100% P)]. Superphosphorylation produced two types of modified casei ns. Solutions made with 220% P casein had low viscosities, which remai ned constant between pH 5 and 9 and between protein concentrations of 0.2 and 0.7%; these solutions remained fluid when exposed to up to 30 mM Ca2+. Solutions made with 160 or 190% P caseins increased in viscos ity as protein concentration and pH increased; the solutions formed ge ls at 1% protein, which increased in elastic modulus, viscous modulus, and complex viscosity as the protein and Ca2+ concentrations increase d. When exposed to Ca2+, gels became more curd-like as protein aggrega ted and then underwent syneresis. Electron microscopy showed that the gel microstructure consisted of an open matrix of folded strands and s heets of casein in irregular sizes that condensed upon exposure to Ca2 +. These unique interactions among proteins and unique rheological pro perties suggest that superphosphorylation could be useful in creating novel dairy foods with added value and enhanced functionality.