Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 21, 1997
Publication Date: N/A
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Interpretive Summary: Casein is unique among food proteins in that it contains high levels of phosphorus which is very important in binding calcium. It is possible to increase or decrease the phosphorus content by chemical treatments. In this study, we increased the amount of phosphorus in casein by chemical treatment so that we might better understand the role of phosphorus in casein interactions when this important protein is used as a food ingredient. Our results showed that caseins with 1.6 to 1.9 times the amount of phosphorus normally found in casein have the ability to form strong elastic gels, especially when calcium is added. These studies demonstrate to the food trade that casein, modified by increasing the phosphorus content, could be very useful in developing novel gelled dairy foods with unique texture.
Technical Abstract: Bovine whole casein was chemically modified using phosphorus oxychloride 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 found per mmol of unmodified casein (100% P). Superphosphorylation produced two types of modified caseins. Solutions made with 220% P casein had low viscosities which remained 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 calcium. Solutions made with 160 or 190% P caseins increased in viscosity as protein concentration and pH increased; they form gels at 1% protein which increased in elastic modulus, viscous modulus, and complex viscosity as the protein and calcium concentrations increased. When exposed to calcium, gels became more curd-like as protein aggregated and then underwent syneresis. Electron microscopy showed that the gel microstructure consisted of an open matrix of folded strands and sheets of casein in irregular sizes that condensed upon exposure to calcium. These unique protein-protein interactions and rheological properties suggest that superphosphorylation could be useful in creating novel added-value dairy fo with enhanced functionality.