SUMMARY. Casein phosphopeptides (CPP) were produced by tryptic hydrolysis of sodium caseinate and further purified by precipitation and chromatography on QAE-Sephadex A-25. Their physico-chemical properties were compared with the properties of an enzymically dephosphorylated equivalent preparation (DPP). Binding of Ca 2+ to the peptides was measured using a Ca selective electrode and was found to increase with pH and to show 1/1 stoicheiometry Ca/P org in CPP at pH 6 -5 a.nd 7-6. Klotz plots indicated equivalent binding sites at these two pH values, but some heterogeneity was seen at pH 3-5. In contrast, DPP did not bind significant amounts of Ca 2+ . CPP effectively inhibited the formation of insoluble calcium phosphates at different Ca/P ratios. The effective CPP concentration was 10 mg/1 and complete stability of calcium phosphate solutions was obtained at about 100 mg/1. This stabilizing effect was dependent on the presence of organic P.

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SUMMARY. A method using low resolution NMR spectroscopy is described for investigating whey protein thermal denaturation. The method is based on measuring at 20 °C changes in water proton transverse (T 2 ) relaxation parameter following the denaturing treatment. This parameter is shown to be sensitive to protein denaturation and not to other phenomena such as gelation. Examples are given for the qualitative study of protein thermal denaturation in whey protein concentrate, /Mactoglobulin, a-lactalbumin, bovine serum albumin and immunoglobulins aqueous solutions and for the quantitative determination of thermal denaturation in whey protein concentrate solutions.

Water proton transverse (T,) relaxation measurements in whey, egg, gelatin, and soybean sols and gels were determined. TZ relaxation in protein sols and gels was a single exponential process, except for oil containing sols which showed a two-phase behavior. The relaxation rates (l/r,) increased linearly with concentration of either protein or oil. For samples containing protein which underwent an irreversible denaturation upon heating, T, relaxation times were longer in the sols than in the gels. In gels, the variation of the Ta relaxation times with temperature was interpreted in terms of an exchange between labile protein protons and water protons.

SUMMARY. A recently described nuclear magnetic resonance (NMR) method was evaluated for its usefulness in studying thermal effects on milk proteins. The increase in water proton T 2 relaxation rate observed during thermal treatment of aqueous whey protein solutions above the denaturing onset temperature paralleled results obtained with the standard Rowland (1938) method. The influence of milk constituents on NMR characteristics was analysed. The NMR response increased with the ionic strength and the addition of caseinate or casein micelles. The relevance of the T 2 relaxation probe for studying thermal modifications of milk proteins is discussed. It is proposed to apply the NMR method for determining either reversible or irreversible thermal denaturation of whey proteins in model systems.