ANALYSIS OF MODIFIED WHOLE CASEIN WITH DIFFERENT PHOSPHORUS CONTENTS USING P-31 NUCLEAR-MAGNETIC-RESONANCE AND FOURIER-TRANSFORM INFRARED-SPECTROSCOPY

The different types of P in modified caseins and the role of P in case in interactions were studied using P-31 nuclear magnetic resonance spe ctroscopy of whole casein with reduced or elevated P concentrations an d using Fourier transform infrared spectroscopy of whole casein with e levated P concentrations. Bovine whole casein (5.7 mmol of P/mmol of c asein, 100% P) was either enzymatically dephosphorylated or chemically superphosphorylated to obtain casein containing 0.4, 3.3, 9.1, 10.6, or 12.5 mmol of bound P/mmol of casein (7, 60, 160, 190, or 220% P, re spectively). The nuclear magnetic resonance spectra showed that all ca sein samples contained serine monophosphates; the caseins containing 1 60, 190, and 220% P also contained additional diphosphates, and the 22 0% P casein contained inorganic phosphate and other di- and polyphosph ates. When the concentration of the 160 and 190% P caseins increased, they gelled, yet the nuclear magnetic resonance spectra did not show a ny differences that were typical of changes in conformation. Analysis by Fourier transform infrared spectroscopy indicated that the addition of covalently bound P to whole casein in any amount did not change th e distribution of extended strand and sheet, helix, loop, and turns in their secondary structures. Study of the phosphates that were bound t o casein and the influence of phosphates on casein interactions improv es the understanding of how casein interacts in food systems.