Sugar-casein interaction in deuterated solutions of bovine and caprine casein as determined by oxygen-17 and carbon-13 nuclear magnetic resonance: a case of preferential interactions.
17O NMR spectroscopy and (13)C NMR spectroscopy have been used to study the mechanism of interaction of sugars with bovine and caprine caseins in D(2)O. The (17)O NMR relaxation results showed in all cases an increase in water of hydration, as a result of added sugar; this was predominantly associated with "trapped" water in the caseins. Analysis of the vir al coefficients, obtained from the (17)O relaxation data, suggested that preferential interactions occur in the sugar-protein solutions. This could be the result of either sugar binding or a solute-solute thermodynamic effect, preferential hydration. The addition of sugars to deuterated solutions of bovine casein and caprine casein high in alpha(s1)-casein had little or no effect on either line width or chemical shifts of the (13)C NMR spectra of these milk proteins. (13)C NMR studies of sucrose, at various concentrations (100-300 mM) in the presence of caprine casein high in alpha(s1)-casein, showed no changes in either chemical shifts or T(1) values. This indicates that the sugar molecules tumble isotropically and therefore neither bind to the protein nor affect viscosity in the protein-sugar studies. All of these data suggest that the preferential exclusion of the sugar from the domain of the caseins results in preferential hydration of the caseins.
Mora-Gutierrez
A
A
Cooperative Agricultural Research Center, Prairie View A&M University, Prairie View, Texas 77446, USA.
Farrell
H M
HM
D000818:Animals; D002241:Carbohydrates / Q000737:chemistry*; D002247:Carbon Isotopes; D002364:Caseins / Q000737:chemistry*; D002417:Cattle; D003903:Deuterium; D006041:Goats; D009682:Magnetic Resonance Spectroscopy; D010103:Oxygen Isotopes; D012996:Solutions
D002241:Carbohydrates; D002247:Carbon Isotopes; D002364:Caseins; D010103:Oxygen Isotopes; D012996:Solutions; D003903:Deuterium