An FTIR spectroscopy study of the interaction between as-casein-bound phosphoryl groups and chitosan

C. FERNÁNDEZ; S.F. AUSAR; R.G. BADINI; L.F. CASTAGNA; I.D. BIANCO; D.M. BELTRAMO

INTERNATIONAL DAIRY JOURNAL

Elsevier

Año: 2003 vol. 13 p. 897 - 901

0958-6946

Fourier-transform infrared spectroscopy was used to study the nature of the linkage and interactions of phosphate ester bonds in as-casein under precipitation by chitosan. We have found that the dianionic stretching band of the covalently bound phosphate ins-casein under precipitation by chitosan. We have found that the dianionic stretching band of the covalently bound phosphate in as-casein at 976 cm1 is sensitive to the ionization state and the binding ofCa 2+ or chitosan. Thus, the neutralization ofthe negative charges ofcarboxylates and phosphates by lowering the pH of as-casein solution from 6.8 to 2.0 led to a dramatic reduction of this signal. Precipitating amounts ofCa 2+ caused a shift in the phosphate signal from 976 to 986 cm1 indicating a direct electrostatic interaction between Ca2+ and phosphate. The interaction of as-casein with low molecular weight chitosan showed a small shift (ca. 2 cm1) in the phosphate peak position as compared with pure as-casein with a pronounced reduction in the phosphate peak amplitude that was about a halfofthat ofcasein alone. When as-casein was precipitated with high molecular weight chitosan, a more noticeable effect occurred as this complex showed only around 25% of the phosphate peak amplitude. The interactions between the phosphate groups covalently bound to as-casein and the amino groups in chitosan seem to induce changes similar to those observed upon protonation ofthe negative charges ofphosphate.s-casein at 976 cm1 is sensitive to the ionization state and the binding ofCa 2+ or chitosan. Thus, the neutralization ofthe negative charges ofcarboxylates and phosphates by lowering the pH of as-casein solution from 6.8 to 2.0 led to a dramatic reduction of this signal. Precipitating amounts ofCa 2+ caused a shift in the phosphate signal from 976 to 986 cm1 indicating a direct electrostatic interaction between Ca2+ and phosphate. The interaction of as-casein with low molecular weight chitosan showed a small shift (ca. 2 cm1) in the phosphate peak position as compared with pure as-casein with a pronounced reduction in the phosphate peak amplitude that was about a halfofthat ofcasein alone. When as-casein was precipitated with high molecular weight chitosan, a more noticeable effect occurred as this complex showed only around 25% of the phosphate peak amplitude. The interactions between the phosphate groups covalently bound to as-casein and the amino groups in chitosan seem to induce changes similar to those observed upon protonation ofthe negative charges ofphosphate.as-casein solution from 6.8 to 2.0 led to a dramatic reduction of this signal. Precipitating amounts ofCa 2+ caused a shift in the phosphate signal from 976 to 986 cm1 indicating a direct electrostatic interaction between Ca2+ and phosphate. The interaction of as-casein with low molecular weight chitosan showed a small shift (ca. 2 cm1) in the phosphate peak position as compared with pure as-casein with a pronounced reduction in the phosphate peak amplitude that was about a halfofthat ofcasein alone. When as-casein was precipitated with high molecular weight chitosan, a more noticeable effect occurred as this complex showed only around 25% of the phosphate peak amplitude. The interactions between the phosphate groups covalently bound to as-casein and the amino groups in chitosan seem to induce changes similar to those observed upon protonation ofthe negative charges ofphosphate.2+ caused a shift in the phosphate signal from 976 to 986 cm1 indicating a direct electrostatic interaction between Ca2+ and phosphate. The interaction of as-casein with low molecular weight chitosan showed a small shift (ca. 2 cm1) in the phosphate peak position as compared with pure as-casein with a pronounced reduction in the phosphate peak amplitude that was about a halfofthat ofcasein alone. When as-casein was precipitated with high molecular weight chitosan, a more noticeable effect occurred as this complex showed only around 25% of the phosphate peak amplitude. The interactions between the phosphate groups covalently bound to as-casein and the amino groups in chitosan seem to induce changes similar to those observed upon protonation ofthe negative charges ofphosphate.2+ and phosphate. The interaction of as-casein with low molecular weight chitosan showed a small shift (ca. 2 cm1) in the phosphate peak position as compared with pure as-casein with a pronounced reduction in the phosphate peak amplitude that was about a halfofthat ofcasein alone. When as-casein was precipitated with high molecular weight chitosan, a more noticeable effect occurred as this complex showed only around 25% of the phosphate peak amplitude. The interactions between the phosphate groups covalently bound to as-casein and the amino groups in chitosan seem to induce changes similar to those observed upon protonation ofthe negative charges ofphosphate.1) in the phosphate peak position as compared with pure as-casein with a pronounced reduction in the phosphate peak amplitude that was about a halfofthat ofcasein alone. When as-casein was precipitated with high molecular weight chitosan, a more noticeable effect occurred as this complex showed only around 25% of the phosphate peak amplitude. The interactions between the phosphate groups covalently bound to as-casein and the amino groups in chitosan seem to induce changes similar to those observed upon protonation ofthe negative charges ofphosphate.as-casein was precipitated with high molecular weight chitosan, a more noticeable effect occurred as this complex showed only around 25% of the phosphate peak amplitude. The interactions between the phosphate groups covalently bound to as-casein and the amino groups in chitosan seem to induce changes similar to those observed upon protonation ofthe negative charges ofphosphate.as-casein and the amino groups in chitosan seem to induce changes similar to those observed upon protonation ofthe negative charges ofphosphate.