Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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Record number 401449
Title Overall Charge and Local Charge Density of Pectin Determines the Enthalpic and Entropic Contributions to Complexation with ß-Lactoglobulin
Author(s) Sperber, B.L.H.M.; Cohen Stuart, M.A.; Schols, H.A.; Voragen, A.G.J.; Norde, W.
Source Biomacromolecules 11 (2010)12. - ISSN 1525-7797 - p. 3578 - 3583.
Department(s) Food Chemistry Group
Physical Chemistry and Colloid Science
Publication type Refereed Article in a scientific journal
Publication year 2010
Keyword(s) isothermal titration calorimetry - polyelectrolyte complexation - milk-proteins - acid - isolate - gum - chromatography - hydrocolloids - association - mechanism
Abstract The complex formation between ß-lactoglobulin and pectins of varying overall charge and local charge density were investigated. Isothermal titration calorimetry experiments were carried out to determine the enthalpic contribution to the complex formation at pH 4.25 and various ionic strengths. Complex formation was found to be an exothermic process for all conditions. Combination with previously published binding constants by Sperber et al. (Sperber, B. L. H. M.; Cohen Stuart, M. A.; Schols, H. A.; Voragen, A. G. J.; Norde, W. Biomacromolecules 2009, 10, 3246-3252) allows for the determination of the changes in the Gibbs energy and the change in entropy of the system upon complex formation between ß-lactoglobulin and pectin. The local charge density of pectin is found to determine the balance between enthalpic and entropic contributions. For a high local charge density pectin, the main contribution to the Gibbs energy is of an enthalpic nature, supported by a favorable entropy effect due to the release of small counterions. A pectin with a low local charge density has a more even distribution of the enthalpic and entropic part to the change of the Gibbs energy. The enthalpic part is reduced due to the lower charge density, while the relative increase of the entropic contribution is thought to be caused by a change in the location of the binding place for pectin on the ß-lactoglobulin molecule. The association of the hydrophobic methyl esters on pectin with an exposed hydrophobic region on ß-lg results in the release of water molecules from the hydrophobic region and surrounding the methyl esters of the pectin molecule. An increase in the ionic strength decreases the enthalpic contribution due to the shielding of electrostatic attraction in favor of the entropic contribution, supporting the idea that the release of water molecules from hydrophobic areas plays a part in the complex formation.
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