O-17 NUCLEAR-MAGNETIC-RESONANCE STUDIES OF BOVINE AND CAPRINE CASEIN HYDRATION AND ACTIVITY IN DEUTERATED SUGAR SOLUTIONS

The hydration of bovine and genetically variable caprine caseins in D2 O solutions of sucrose and lactose was investigated by oxygen-17 NMR a nd fitted by nonlinear regression analysis. A charge-charge interactio n model was employed to analyze the transverse relaxation (1/T-2) data . Lactose caused increased hydration of the bovine casein and the capr ine casein naturally low in alpha(s1)-casein, whereas sucrose led to i ncreased hydration of the caprine casein naturally high in alpha(s1)-c asein. At pD 7.20 and 21 degrees C the effect of charge-charge repulsi ve interactions on the native caseins generally leads to decreased pro tein stability in bovine and caprine caseins. However, addition of sug ars causes stronger (attractive) interactions yielding more stable cas ein complexes with increased hydration. The calculated preferential bi nding term -(partial derivative g(s)/partial derivative g(p)) for case in mixtures suggests that sucrose and lactose are ''preferentially'' e xcluded from these milk proteins, yielding greater access to much of t he aqueous compartment. This is consistent with the view that sugars l ead to the stabilization of proteins in nonfrozen, aqueous systems.